Dinosaurs Fossil range: Late Triassic - Late Cretaceous (excluding Aves)
Mounted skeletons of Tyrannosaurus (left) and Apatosaurus (right) at the American Museum of Natural History. The Late Triassic (also known as Upper Triassic, or Keuper) is the third and final of three epochs of the Triassic period. Late Cretaceous (100mya - 65mya refers to the second half of the Cretaceous Period, named after the famous white Chalk cliffs of southern England Birds ( class Aves) are bipedal endothermic ( Warm-blooded) Vertebrate animals that lay eggs. Tyrannosaurus ( or, meaning 'tyrant lizard' is a Genus of Theropod Dinosaur. The American Museum of Natural History ( AMNH) located on the Upper West Side, Manhattan, New York, USA is one of the largest and most
Scientific classification
Kingdom: Animalia Phylum: Chordata Subphylum: Vertebrata Class: Sauropsida Subclass: Diapsida Infraclass: Archosauromorpha Superorder: Dinosauria Owen, 1842
Orders and suborders
Ornithischia † Cerapoda † Thyreophora † Saurischia Sauropodomorpha † Theropoda

Dinosaurs were the dominant vertebrate animals of terrestrial ecosystems for over 160 million years, from the late Triassic period (about 230 million years ago) to the end of the Cretaceous period (65 million years ago), when most of them became extinct in the Cretaceous–Tertiary extinction event. Chordates ( Phylum Chordata) are a group of Animals that includes the Vertebrates together with several closely related Invertebrates Vertebrates are members of the Subphylum Vertebrata, Chordates with backbones or spinal columns The grouping sometimes includes Reptiles, or members of the class Reptilia are air-breathing Cold-blooded Vertebrates that have skin covered in scales as opposed to hair or feathers Diapsids ("two arches" are a group of Reptiles that developed two holes ( Temporal fenestra) in each side of their Skulls about 300 Million Archosauromorpha ( Greek for "ruling lizard forms" is an Infraclass of Diapsid Reptiles that first appeared during the late Permian Sir Richard Owen KCB ( Lancaster, July 20 1804 &ndash December 18 1892) was an English Biologist This article is about the taxonomic rank for the sequence of species in a taxonomic list see Taxonomic order In scientific classification used This article is about the taxonomic rank for the sequence of species in a taxonomic list see Taxonomic order In scientific classification used Ornithischia (ɔrnɪˈθɪskiə) or Predentata is an extinct order of beaked herbivorous Dinosaurs The name ornithischia In Biology and Ecology, extinction is the cessation of existence of a Species or group of taxa. Cerapoda (siːˈrɒpədə is a Clade or suborder of the order Ornithischia. In Biology and Ecology, extinction is the cessation of existence of a Species or group of taxa. The Thyreophora ("shield bearers" often known simply as "armored dinosaurs" - Greek: θυρεος, a large oblong shield like a door and In Biology and Ecology, extinction is the cessation of existence of a Species or group of taxa. Saurischia (sɔːˈrɪskiə, from the Greek sauros ( σαυρος) meaning 'lizard' and ischion ( ισχιον) meaning 'hip joint' The Sauropodomorpha (sɔˌrɒpədəˈmɔrfə were a group of long-necked herbivorous Dinosaurs that eventually dropped down on all fours and became In Biology and Ecology, extinction is the cessation of existence of a Species or group of taxa. Theropods (ˈθɪərəpɒd theropoda /θiːˈrɒpədə/ 'beast feet' are a group of Bipedal Saurischian Dinosaurs Although they were primarily Vertebrates are members of the Subphylum Vertebrata, Chordates with backbones or spinal columns The grouping sometimes includes An ecosystem is a natural unit consisting of all plants animals and micro-organisms( Biotic factors in an area functioning together with all of the non-living physical ( The Triassic is a geologic period and system that extends from about 251 to 199 Ma (million years ago Annum is one form of the Latin noun meaning Year, not a form normally used for derivatives in modern languages the accusative singular The Cretaceous (kriːˈteɪʃəs, usually abbreviated 'K' for its German translation "Kreide" is a geologic period and system, reaching from the end of The Cretaceous–Tertiary extinction event, which occurred approximately ( Ma) was a large-scale mass extinction of animal and plant species in a geologically

The discovery in 1862 of Archaeopteryx first suggested a close relationship between dinosaurs and birds; aside from the presence of fossilized feather impressions, Archaeopteryx was very similar to the contemporary small predatory dinosaur Compsognathus. Archaeopteryx, sometimes referred to by its German name Urvogel ("original bird" or "first bird" is the earliest and most primitive Bird Compsognathus ( Greek kompsos/κομψος; "elegant" "refined" or "dainty" and gnathos/γναθος; "jaw" Research since the 1970s indicates that theropod dinosaurs are most likely the ancestors of birds; in fact, most paleontologists regard birds as the only surviving dinosaurs and some believe dinosaurs and birds should be put together under one biological class. Theropods (ˈθɪərəpɒd theropoda /θiːˈrɒpədə/ 'beast feet' are a group of Bipedal Saurischian Dinosaurs Although they were primarily Birds ( class Aves) are bipedal endothermic ( Warm-blooded) Vertebrate animals that lay eggs. ^[1] Crocodilians are the other surviving close relatives of dinosaurs, and both groups are members of the Archosauria, a group of reptiles that first appeared in the very late Permian and became dominant in the mid-Triassic. Crocodilia is an order of large Reptiles that appeared about 84 million years ago in the late Cretaceous Period ( Campanian stage Archosaurs ( Greek for 'ruling lizards' are a group of Diapsid Reptiles represented by Modern birds and Crocodilians This group also Reptiles, or members of the class Reptilia are air-breathing Cold-blooded Vertebrates that have skin covered in scales as opposed to hair or feathers The Permian is a geologic period and system that extends from 299

For about the first half of the 20th century, both scientists and the general public regarded dinosaurs as slow, unintelligent cold-blooded animals. Cold-blooded organisms (called poikilotherms - "of varying temperature" maintain their body temperatures in ways different from Mammals and Birds However, the bulk of research since the 1970s has supported the view that they were active animals with elevated metabolisms, and often with adaptations for social interactions. The " Dinosaur renaissance " was a small-scale scientific revolution started in the late 1960s which led to renewed academic and popular interest in Dinosaurs This change of view was strongly influenced by evidence of the descent of birds from theropod dinosaurs.

Since the first dinosaur fossils were recognized in the early nineteenth century, mounted dinosaur skeletons have become major attractions at museums around the world. FOSSIL is a standard protocol for allowing serial communication for Telecommunications programs under the DOS Operating system. Dinosaurs have become a part of world culture and remain consistently popular among children and adults. They have been featured in best-selling books and films (notably Jurassic Park), and new discoveries are regularly covered by the media. Jurassic Park is a Science fiction Novel that was written by Michael Crichton and published in 1990. The news media refers to the section of the Mass media that focuses on presenting current News to the public

The term "dinosaur" was first coined 1842, by Sir Richard Owen and derives from Greek δεινός (deinos) "terrible, stiff, masterly, skillful" + σαῦρος (sauros) "lizard". Sir Richard Owen KCB ( Lancaster, July 20 1804 &ndash December 18 1892) was an English Biologist Greek (el ελληνική γλώσσα or simply el ελληνικά — "Hellenic" is an Indo-European language, spoken today by 15-22 million people mainly It is sometimes used informally to describe other prehistoric reptiles, such as the pelycosaur Dimetrodon, the winged pterosaurs, and the aquatic ichthyosaurs, plesiosaurs and mosasaurs, although none of these were dinosaurs. The pelycosaurs (from Greek πηλυξ pelyx meaning 'bowl' and σαυρος sauros meaning 'lizard' were primitive Late Paleozoic Dimetrodon (daɪˈmɛtɹəʊˌdɒn meaning "two measures of teeth" was a Predatory Synapsid (' Mammal-like reptile ' Genus For other meanings see Pterodactyl (disambiguation. Pterosaurs (ˈtɛrəsɔr from the Greek πτερόσαυρος pterosauros Ichthyosaurs ( Greek for 'fish lizard' - ιχθυς / ichthyos meaning 'fish' and σαυρος / sauros meaning 'lizard' were giant Plesiosaurs (ˈpliːziəˌsɔɹ ( Greek: plesios/πλησιος meaning 'near' or 'close to' and sauros/σαυρος meaning Mosasaurs (from Latin Mosa meaning the ' Meuse river ' in the Netherlands and Greek sauros meaning 'lizard' were serpentine marine

In colloquial English "dinosaur" is sometimes used to describe an obsolete or unsuccessful thing or person, despite the dinosaurs' 160 million year reign and the global abundance and diversity of their descendants, the birds. This usage became common while dinosaurs were regarded as cold-blooded and sluggish.

Contents 1 What is a dinosaur? 1.1 Original definition 1.2 Modern definition 1.3 General description 1.4 Distinguishing features 2 Natural history 2.1 Origins and early evolution 2.2 Classification 2.3 Evolution and paleobiogeography 3 Paleobiology 3.1 Size 3.1.1 Largest and smallest 3.2 Behavior 3.3 Physiology 3.4 Soft tissue and DNA 4 Feathers and the origin of birds 4.1 Feathers 4.2 Skeleton 4.3 Soft anatomy 4.4 Reproductive biology 4.5 Behavioral evidence 5 Extinction 5.1 Impact event 5.2 Deccan Traps 5.3 Possible Paleocene survivors 6 History of discovery 6.1 The "dinosaur renaissance" 7 Cultural depictions 8 Religious views 9 See also 10 Notes and references 11 General references 12 See also 13 External links

What is a dinosaur?

Original definition

The taxon Dinosauria was formally named in 1842 by English palaeontologist Richard Owen, who used it to refer to the "distinct tribe or sub-order of Saurian Reptiles" that were then being recognized in England and around the world. A taxon (plural taxa) or taxonomic unit, is a name designating an organism or a group of Organisms In Biological nomenclature according to The English people (from the adjective in Englisc) are a Nation and Ethnic group native to England who predominantly speak English Palaeontology redirects here For the Scientific journal, see Palaeontology (journal. Sir Richard Owen KCB ( Lancaster, July 20 1804 &ndash December 18 1892) was an English Biologist ^[2] The term is derived from the Greek words δεινός (deinos meaning "terrible", "fearsome", or "formidable") and σαύρα (saura meaning "lizard" or "reptile"). The Ancient Greek language is the historical stage in the development of the Hellenic language family spanning the Archaic (c Though the taxonomic name has often been interpreted as a reference to dinosaurs' teeth, claws, and other fearsome characteristics, Owen intended it merely to evoke their size and majesty. ^[3]

Modern definition

Under phylogenetic taxonomy, dinosaurs are usually defined as all descendants of the most recent common ancestor of Triceratops and modern birds. Triceratops (traɪˈsɛrətɒps is an extinct Genus of herbivorous ceratopsid Dinosaur which lived during the late Maastrichtian Birds ( class Aves) are bipedal endothermic ( Warm-blooded) Vertebrate animals that lay eggs. ^[4] It has also been suggested that Dinosauria be defined as all of the descendants of the most recent common ancestor of Megalosaurus and Iguanodon, because these were two of the three genera cited by Richard Owen when he recognized the Dinosauria. Megalosaurus (meaning "Great Lizard" from Greek, μεγαλο-/megalo- meaning 'big' 'tall' or 'great' and σαυρος/sauros Iguanodon (ɪˈgwɑːnədɒn or /ɪˈgwænədɒn/ meaning " Iguana Tooth " is a Genus of Ornithopod Dinosaur ^[5] Both definitions result in the same set of animals being defined as dinosaurs, including theropods (mostly bipedal carnivores), sauropodomorphs (mostly large herbivorous quadrupeds with long necks and tails), ankylosaurians (armored herbivorous quadrupeds), stegosaurians (plated herbivorous quadrupeds), ceratopsians (herbivorous quadrupeds with horns and frills), and ornithopods (bipedal or quadrupedal herbivores including "duck-bills"). Theropods (ˈθɪərəpɒd theropoda /θiːˈrɒpədə/ 'beast feet' are a group of Bipedal Saurischian Dinosaurs Although they were primarily Bipedalism is a form of Terrestrial locomotion where an organism moves by means of its two rear limbs A carnivore (ˈkɑrnɪvɔər meaning 'meat eater' ( Latin carne meaning 'flesh' and vorare meaning 'to devour' is any animal with a diet consisting The Sauropodomorpha (sɔˌrɒpədəˈmɔrfə were a group of long-necked herbivorous Dinosaurs that eventually dropped down on all fours and became Herbivory is a form of Predation in which an Organism, known as a herbivore, consumes principally Autotrophs ref name=Campbell>Campbell Quadrupedalism (from Latin meaning "four legs" is a form of land animal locomotion using four legs. Ankylosauria is a group of Herbivorous Dinosaurs of the order Ornithischia. Known colloquially as stegosaurs the Stegosauria are a group of herbivorous Dinosaurs of the Jurassic and Early Cretaceous Periods Ceratopsia or Ceratopia (ˌsɛrəˈtɒpsiə/ /ˌsɛrəˈtoʊpiə Greek: "horned faces" is a group of herbivorous, beaked Dinosaurs Ornithopods (ɔrˈnɪθoʊpɒd are a group of bird-hipped Dinosaurs that started out as small Bipedal running grazers and grew in size and These definitions are written to correspond with scientific conceptions of dinosaurs that predate the modern use of phylogenetics. The continuity of meaning is intended to prevent confusion about what the term "dinosaur" means.

There is an almost universal consensus among paleontologists that birds are the descendants of theropod dinosaurs. Using the strict cladistical definition that all descendants of a single common ancestor must be included in a group for that group to be natural, birds are dinosaurs and dinosaurs are, therefore, not extinct. Cladistics is the hierarchical classification of Species based on evolutionary ancestry Birds are classified by most paleontologists as belonging to the subgroup Maniraptora, which are coelurosaurs, which are theropods, which are saurischians, which are dinosaurs. Maniraptora ("hand snatchers" is a Clade of Coelurosaurian Dinosaurs which includes the Birds and the dinosaurs that were more closely For the prehistoric gliding reptile see Coelurosauravus. Coelurosauria (sɨˌljʊərəˈsɔriə is defined as the clade containing all Theropod Saurischia (sɔːˈrɪskiə, from the Greek sauros ( σαυρος) meaning 'lizard' and ischion ( ισχιον) meaning 'hip joint' ^[6]

From the point of view of cladistics, birds are dinosaurs, but in ordinary speech the word "dinosaur" does not include birds. Additionally, referring to dinosaurs that are not birds as "non-avian dinosaurs" is cumbersome. For clarity, this article will use "dinosaur" as a synonym for "non-avian dinosaur". The term "non-avian dinosaur" will be used for emphasis as needed. It is also technically correct to refer to dinosaurs as a distinct group under the older Linnaean classification system, which accepts paraphyletic taxa that exclude some descendants of a single common ancestor. In Phylogenetics, a group of organisms is said to be paraphyletic if the group contains its most recent common ancestor but does not contain all

General description

Using one of the above definitions, dinosaurs (aside from birds) can be generally described as terrestrial archosaurian reptiles with limbs held erect beneath the body, that existed from the Late Triassic (first appearing in the Carnian faunal stage) to the Late Cretaceous (going extinct at the end of the Maastrichtian). Archosaurs ( Greek for 'ruling lizards' are a group of Diapsid Reptiles represented by Modern birds and Crocodilians This group also Reptiles, or members of the class Reptilia are air-breathing Cold-blooded Vertebrates that have skin covered in scales as opposed to hair or feathers Terrestrial locomotion has Evolved as Animals adapted from aquatic to terrestrial environments The Late Triassic (also known as Upper Triassic, or Keuper) is the third and final of three epochs of the Triassic period. The Carnian (less commonly Karnian) is the lowermost stage of the Upper Triassic series (or earliest age of the Late Triassic Late Cretaceous (100mya - 65mya refers to the second half of the Cretaceous Period, named after the famous white Chalk cliffs of southern England The Maastrichtian is the last stage of the Cretaceous period, and therefore of the Mesozoic era. ^[7] Many prehistoric animals are popularly conceived of as dinosaurs, such as ichthyosaurs, mosasaurs, plesiosaurs, pterosaurs, and Dimetrodon, but are not classified scientifically as dinosaurs. Dimetrodon (daɪˈmɛtɹəʊˌdɒn meaning "two measures of teeth" was a Predatory Synapsid (' Mammal-like reptile ' Genus Marine reptiles like ichthyosaurs, mosasaurs, and plesiosaurs were neither terrestrial nor archosaurs; pterosaurs were archosaurs but not terrestrial; and Dimetrodon was a Permian animal more closely related to mammals. The Permian is a geologic period and system that extends from 299 ^[8] Dinosaurs were the dominant terrestrial vertebrates of the Mesozoic, especially the Jurassic and Cretaceous. The Jurassic is a geologic period and system that extends from about Ma (million years ago to  Ma that is from the end of the Triassic to the beginning Other groups of animals were restricted in size and niches; mammals, for example, rarely exceeded the size of a cat, and were generally rodent-sized carnivores of small prey. ^[9] One notable exception is Repenomamus giganticus, a triconodont weighing between 12 kilograms (26 lb) and 14 kilograms (31 lb) that is known to have eaten small dinosaurs like young Psittacosaurus. Repenomamus is the largest Mammal known from the Cretaceous period of the Mesozoic, and it is the mammal for which there is the best evidence Triconodonta (also known as Eutriconodonta) is the generic name for a group of early Mammals which were close relatives of the ancestors of all present-day mammals Psittacosaurus ( or, from the Greek for ' Parrot Lizard ' is a Genus of Psittacosaurid Ceratopsian ^[10]

Dinosaurs were an extremely varied group of animals; according to a 2006 study, over 500 dinosaur genera have been identified with certainty so far, and the total number of genera preserved in the fossil record has been estimated at around 1,850, nearly 75% of which remain to be discovered. ^[11] An earlier study predicted that about 3,400 dinosaur genera existed, including many which would not have been preserved in the fossil record. ^[12] Some were herbivorous, others carnivorous. Some dinosaurs were bipeds, some were quadrupeds, and others, such as Ammosaurus and Iguanodon, could walk just as easily on two or four legs. Ammosaurus (ˌæməˈsɔrəs "sand lizard" is a Genus of Sauropodomorph Dinosaur from the Early Jurassic Period of Iguanodon (ɪˈgwɑːnədɒn or /ɪˈgwænədɒn/ meaning " Iguana Tooth " is a Genus of Ornithopod Dinosaur Many had bony armor, or cranial modifications like horns and crests. Armor (or armour) in animals is external or superficial protection against attack by predators formed as part of the body (rather than the behavioural use of protective external Although known for large size, many dinosaurs were human-sized or smaller. Dinosaur remains have been found on every continent on Earth, including Antarctica. ^[13] Despite their diversity and dominance, however, dinosaurs (other than birds) are not known to have spread into aquatic or aerial niches.

Distinguishing features

While recent discoveries have made it more difficult to present a universally agreed-upon list of dinosaurs' distinguishing features, nearly all dinosaurs discovered so far share certain modifications to the ancestral archosaurian skeleton. Archosaurs ( Greek for 'ruling lizards' are a group of Diapsid Reptiles represented by Modern birds and Crocodilians This group also Although some later groups of dinosaurs featured further modified versions of these traits, they are considered typical across Dinosauria; the earliest dinosaurs had them and passed them on to all their descendants. Such common features across a taxonomic group are called synapomorphies. In Evolutionary biology, a synapomorphy is a derived Character state shared by two or more terminal groups ( taxa included in a Cladistic analysis

Dinosaur synapomorphies include an elongated crest on the humerus, or upper arm bone, to accommodate the attachment of deltopectoral muscles; a shelf at the rear of the ilium, or main hip bone; a tibia, or shin bone, featuring a broad lower edge and a flange pointing out and to the rear; and an ascending projection on the astragalus, one of the ankle bones, which secures it to the tibia. The humerus is a Long bone in the Arm or Forelimb that runs from the Shoulder to the Elbow. The clavipectoral triangle (or deltopectoral triangle) is an anatomical triangle bordered by the following structures Pectoralis major The ilium of the Pelvis is divisible into two parts the body and the ala the separation is indicated on the top surface by a curved line the arcuate line and on the The tibia, shinbone, or shankbone is the larger and stronger of the two Bones in the Leg below the Knee in vertebrates and connects See Talus for other meanings of the word The talus bone or astragalus of the Ankle joint connects the leg to the foot ^[14]

A variety of other skeletal features were shared by many dinosaurs. However, because they were either common to other groups of archosaurs or were not present in all early dinosaurs, these features are not considered to be synapomorphies. Archosaurs ( Greek for 'ruling lizards' are a group of Diapsid Reptiles represented by Modern birds and Crocodilians This group also For example, as diapsid reptiles, dinosaurs ancestrally had two pairs of temporal fenestrae (openings in the skull behind the eyes), and as members of the diapsid group Archosauria, had additional openings in the snout and lower jaw. Diapsids ("two arches" are a group of Reptiles that developed two holes ( Temporal fenestra) in each side of their Skulls about 300 Million An antorbital fenestra is an opening in the Skull, in front of the eye sockets ^[15] Additionally, several characteristics once thought to be synapomorphies are now known to have appeared before dinosaurs, or were absent in the earliest dinosaurs and independently evolved by different dinosaur groups. These include an elongated scapula, or shoulder blade; a sacrum composed of three or more fused vertebrae (three are found in some other archosaurs, but only two are found in Herrerasaurus);^[14] and an acetabulum, or hip socket, with a hole at the center of its inside surface (closed in Saturnalia, for example). In Anatomy, the scapula, omo, or shoulder blade, is the Bone that connects the Humerus (arm bone with the Clavicle (collar The sacrum is a large triangular bone at the base of the spine and at the upper and back part of the Pelvic cavity, where it is inserted like a wedge between A vertebra (plural vertebrae) is an individual Irregular bone in the spinal or Vertebral column ( aka ischis a flexuous and flexible column Herrerasaurus (meaning "Herrera's lizard" after the name of the rancher who discovered the first Fossil of the animal was one of the earliest The acetabulum is a concave surface of the Pelvis. The head of the femur meets with the pelvis at the acetabulum forming the hip Joint Saturnalia is a Genus of very early Saurischian Dinosaur, from the Carnian Faunal stage of the late Triassic ^[16] Another difficulty of determining distinctly dinosaurian features is that early dinosaurs and other archosaurs from the Late Triassic are often poorly known and were similar in many ways; these animals have sometimes been misidentified in the literature. ^[17]

Dinosaurs stood erect in a manner similar to most modern mammals, but distinct from most other reptiles, whose limbs sprawl out to either side. __FORCETOC__ See also Evolutionary history of life The evolution of mammals from Synapsids (mammal-like " Reptiles quot was a gradual process ^[18] Their posture was due to the development of a laterally-facing recess in the pelvis (usually an open socket) and a corresponding inwardly-facing distinct head on the femur. ^[19] Their erect posture enabled dinosaurs to breathe easily while moving, which likely permitted stamina and activity levels that surpassed those of "sprawling" reptiles. Carrier's constraint is the observation that air-breathing Vertebrates which have two Lungs and flex their bodies sideways during Locomotion find it very ^[20] Erect limbs probably also helped support the evolution of large size by reducing bending stresses on limbs. ^[21] Some non-dinosaurian archosaurs, including rauisuchians, also had erect limbs but achieved this by a "pillar erect" configuration of the hip joint, where instead of having a projection from the femur insert on a socket on the hip, the upper pelvic bone was rotated to form an overhanging shelf. Rauisuchia are a poorly known assemblage of predatory and mostly large (often 4 to 6 meters Triassic Archosaurs Originally it was believed that they were related The ilium of the Pelvis is divisible into two parts the body and the ala the separation is indicated on the top surface by a curved line the arcuate line and on the ^[21]

Natural history

Origins and early evolution

For a long time many scientists thought dinosaurs were polyphyletic with multiple groups of unrelated "dinosaurs" evolving due to similar pressures,^[22][23][24] but dinosaurs are now known to have formed a single group. In Phylogenetics, a Taxon is polyphyletic ( Greek for "of many races" if the trait its members have in common evolved separately in different ^[25][14]

Dinosaurs diverged from their archosaur ancestors approximately 230 million years ago during the Middle to Late Triassic period, roughly 20 million years after the Permian-Triassic extinction event wiped out an estimated 95% of all life on Earth. Archosaurs ( Greek for 'ruling lizards' are a group of Diapsid Reptiles represented by Modern birds and Crocodilians This group also The Triassic is a geologic period and system that extends from about 251 to 199 Ma (million years ago The Permian–Triassic (P–Tr extinction event, informally known as the Great Dying, was an Extinction event that occurred, and 70 percent of terrestrial ^{[26] [27]} Radiometric dating of the rock formation that contained fossils from the early dinosaur genus Eoraptor establishes its presence in the fossil record at this time. Radiometric dating (often called radioactive dating) is a technique used to date materials usually based on a comparison between the observed abundance of a naturally occurring This is a List of rock formations meaning isolated scenic or spectacular surface rock outcrops A genus (plural genera from Γένος Latin genus "descent family type gender" is a low-level Taxonomic Eoraptor was one of the world's earliest Dinosaurs It was a two-legged meat-eater that lived between 230 and 225  Million years ago Paleontologists believe Eoraptor resembles the common ancestor of all dinosaurs;^[28] if this is true, its traits suggest that the first dinosaurs were small, bipedal predators. A group of organisms is said to have common descent if they have a common Ancestor. ^[29] The discovery of primitive, dinosaur-like ornithodirans such as Marasuchus and Lagerpeton in Argentinian Middle Triassic strata supports this view; analysis of recovered fossils suggests that these animals were indeed small, bipedal predators. Ornithodira is a Clade within the larger group Archosauria In 1986 Jacques Gauthier coined the name for a node clade containing the last common Marasuchus is a genus of Dinosaur -like Ornithodiran from the middle Triassic Period of Argentina. Lagerpeton is the name given to a genus of basal dinosauromorph from the Ladinian (Middle Triassic) For a topic outline on this subject see List of basic Argentina topics. The Middle Triassic (also known as Muschelkalk) is the second of three epochs of the Triassic period.

When dinosaurs appeared, terrestrial habitats were occupied by various types of basal archosaurs and therapsids, such as aetosaurs, cynodonts, dicynodonts, ornithosuchids, rauisuchias, and rhynchosaurs. Therapsids are an order of Synapsids (Class Synapsida Traditionally synapsids were referred to as Reptiles and were known as The Aetosaurs (literally "Eagle Lizards" ( family) Stagonolepididae, Order Aetosauria) are an Extinct Clade of heavily Cynodonts, or 'dog teeth' are a taxon of Therapsids which includes modern mammals and their extinct close relatives The Dicynodontia are a Taxon of Therapsids or Mammal-like reptiles. Ornithosuchidae is an Extinct family of quadrupedal and facultatively bipedal Crurotarsan Archosaurs These carnivores were Rauisuchia are a poorly known assemblage of predatory and mostly large (often 4 to 6 meters Triassic Archosaurs Originally it was believed that they were related Rhynchosaurs were a group of unusual Triassic Diapsid Reptiles related to the archosaurs. Most of these other animals became extinct in the Triassic, in one of two events. First, at about the boundary between the Carnian and Norian faunal stages (about 215 million years ago), dicynodonts and a variety of basal archosauromorphs, including the prolacertiforms and rhynchosaurs, became extinct. The Carnian (less commonly Karnian) is the lowermost stage of the Upper Triassic series (or earliest age of the Late Triassic The Norian Stage was a portion of the Triassic Geological period. Archosauromorpha ( Greek for "ruling lizard forms" is an Infraclass of Diapsid Reptiles that first appeared during the late Permian Prolacertiformes (sometimes called protorosaurs) were an order of archosauromorph Reptiles that lived during the Permian and Triassic This was followed by the Triassic-Jurassic extinction event (about 200 million years ago), that saw the end of most of the other groups of early archosaurs, like aetosaurs, ornithosuchids, phytosaurs, and rauisuchians. Phytosaurs - family Phytosauridae or Parasuchidae - were a group of large (2 to 12 meters long - average size 3 to 4 meters semi-aquatic predatory These losses left behind a land fauna of crocodylomorphs, dinosaurs, mammals, pterosaurians, and turtles. The Crocodylomorpha are an important group of Archosaurs that include the Crocodilians and their extinct relatives Mammals ( class Mammalia) are a class of Vertebrate Animals characterized by the presence of Sweat glands, including sweat glands For other meanings see Pterodactyl (disambiguation. Pterosaurs (ˈtɛrəsɔr from the Greek πτερόσαυρος pterosauros Turtles are Reptiles of the Order Testudines (all living turtles belong to the Crown group Chelonia) most of ^[14]

The first few lines of primitive dinosaurs diversified through the Carnian and Norian stages of the Triassic, most likely by occupying the niches of groups that became extinct. An adaptive radiation is a rapid Evolutionary radiation characterized by an increase in the morphological and ecological diversity of a single rapidly diversifying lineage The Carnian (less commonly Karnian) is the lowermost stage of the Upper Triassic series (or earliest age of the Late Triassic The Norian Stage was a portion of the Triassic Geological period. Traditionally, dinosaurs were thought to have replaced the variety of other Triassic land animals by proving superior through a long period of competition. Competition can be defined as an interaction between Organisms or Species, in which the fitness of one is lowered by the presence of another This now appears unlikely, for several reasons. Dinosaurs do not show a pattern of steadily increasing in diversity and numbers, as would be predicted if they were competitively replacing other groups; instead, they were very rare through the Carnian, making up only 1-2% of individuals present in faunas. Fauna is all of the Animal life of any particular region or time In the Norian, however, after the extinction of several other groups, they became significant components of faunas, representing 50-90% of individuals. Also, what had been viewed as a key adaptation of dinosaurs, their erect stance, is now known to have present in several contemporaneous groups that were not as successful (aetosaurs, ornithosuchids, rauisuchians, and some groups of crocodylomorphs). Finally, the Late Triassic itself was a time of great upheaval in life, with shifts in plant life, marine life, and climate. ^[14]

Classification

Main article: Dinosaur classification

Dinosaurs (including birds) are archosaurs, like modern crocodilians. Dinosauria is a Clade of Archosaurs within the Phylum Chordata. Archosaurs ( Greek for 'ruling lizards' are a group of Diapsid Reptiles represented by Modern birds and Crocodilians This group also Crocodilia is an order of large Reptiles that appeared about 84 million years ago in the late Cretaceous Period ( Campanian stage Archosaurs' diapsid skulls have two holes, called temporal fenestrae, located where the jaw muscles attach, and an additional antorbital fenestra in front of the eyes. Diapsids ("two arches" are a group of Reptiles that developed two holes ( Temporal fenestra) in each side of their Skulls about 300 Million An antorbital fenestra is an opening in the Skull, in front of the eye sockets Most reptiles (including birds) are diapsids; mammals, with only one temporal fenestra, are called synapsids; and turtles, with no temporal fenestra, are anapsids. Synapsids ('fused arch' also known as theropsids ('beast face' are a class of Animals that includes Mammals and everything closer to mammals than Turtles are Reptiles of the Order Testudines (all living turtles belong to the Crown group Chelonia) most of An anapsid is an Amniote whose skull does not have openings near the temples While "anapsid reptiles" or "anapsida" are traditionally Anatomically, dinosaurs share many other archosaur characteristics, including teeth that grow from sockets rather than as direct extensions of the jawbones. Within the archosaur group, dinosaurs are differentiated most noticeably by their gait. Dinosaur legs extend directly beneath the body, whereas the legs of lizards and crocodylians sprawl out to either side.

Collectively, dinosaurs are usually regarded as a superorder or an unranked clade. This article is about the taxonomic rank for the sequence of species in a taxonomic list see Taxonomic order In scientific classification used A clade is a taxonomic group comprising a single Common ancestor and all the descendants of that ancestor They are divided into two orders, Saurischia and Ornithischia, depending upon pelvic structure. This article is about the taxonomic rank for the sequence of species in a taxonomic list see Taxonomic order In scientific classification used Saurischia (sɔːˈrɪskiə, from the Greek sauros ( σαυρος) meaning 'lizard' and ischion ( ισχιον) meaning 'hip joint' Ornithischia (ɔrnɪˈθɪskiə) or Predentata is an extinct order of beaked herbivorous Dinosaurs The name ornithischia The pelvis (pl pelvises or pelves) or pelvic girdle is the irregular bony structure located at the base of the spine (properly known Saurischia includes those taxa sharing a more recent common ancestor with birds than with Ornithischia, while Ornithischia includes all taxa sharing a more recent common ancestor with Triceratops than with Saurischia. A taxon (plural taxa) or taxonomic unit, is a name designating an organism or a group of Organisms In Biological nomenclature according to Triceratops (traɪˈsɛrətɒps is an extinct Genus of herbivorous ceratopsid Dinosaur which lived during the late Maastrichtian Saurischians ('lizard-hipped', from the Greek sauros (σαυρος) meaning 'lizard' and ischion (ισχιον) meaning 'hip joint') retained the hip structure of their ancestors, with a pubis bone directed cranially, or forward. The Ancient Greek language is the historical stage in the development of the Hellenic language family spanning the Archaic (c For the bone in many mammals often called the penis bone see Baculum The android pubic bone is the Ventral and Anterior In fields of Anatomy, anatomical terms of location are descriptive terms to help identify relative positions or directions within a species ^[19] This basic form was modified by rotating the pubis backward to varying degrees in several groups (Herrerasaurus,^[30] therizinosauroids,^[31] dromaeosaurids,^[32] and birds^[6]). Herrerasaurus (meaning "Herrera's lizard" after the name of the rancher who discovered the first Fossil of the animal was one of the earliest Therizinosaurs (or segnosaurs) were theropod Dinosaurs and members of the Clade Therizinosauroidea Dromaeosauridae is a family of Bird -like Theropod Dinosaurs They were small to medium-sized feathered Carnivores that flourished in the Birds ( class Aves) are bipedal endothermic ( Warm-blooded) Vertebrate animals that lay eggs. Saurischia includes the theropods (bipedal and mostly carnivores, except for birds) and sauropodomorphs (long-necked quadrupedal herbivores). Theropods (ˈθɪərəpɒd theropoda /θiːˈrɒpədə/ 'beast feet' are a group of Bipedal Saurischian Dinosaurs Although they were primarily The Sauropodomorpha (sɔˌrɒpədəˈmɔrfə were a group of long-necked herbivorous Dinosaurs that eventually dropped down on all fours and became Herbivory is a form of Predation in which an Organism, known as a herbivore, consumes principally Autotrophs ref name=Campbell>Campbell

By contrast, ornithischians ('bird-hipped', from the Greek ornitheios (ορνιθειος) meaning 'of a bird' and ischion (ισχιον) meaning 'hip joint') had a pelvis that superficially resembled a bird's pelvis: the pubis bone was oriented caudally (rear-pointing). The Ancient Greek language is the historical stage in the development of the Hellenic language family spanning the Archaic (c For the bone in many mammals often called the penis bone see Baculum The android pubic bone is the Ventral and Anterior In fields of Anatomy, anatomical terms of location are descriptive terms to help identify relative positions or directions within a species Unlike birds, the ornithischian pubis also usually had an additional forward-pointing process. Ornithischia includes a variety of herbivores. (NB: the terms "lizard hip" and "bird-hip" are misnomers — birds evolved from dinosaurs with "lizard hips". )

Saurischian pelvis structure (left side)

Tyrannosaurus pelvis (showing saurischian structure - left side)

Ornithischian pelvis structure (left side). Saurischia (sɔːˈrɪskiə, from the Greek sauros ( σαυρος) meaning 'lizard' and ischion ( ισχιον) meaning 'hip joint' Tyrannosaurus ( or, meaning 'tyrant lizard' is a Genus of Theropod Dinosaur. Ornithischia (ɔrnɪˈθɪskiə) or Predentata is an extinct order of beaked herbivorous Dinosaurs The name ornithischia

Edmontosaurus pelvis (showing ornithischian structure - left side)

The following is a simplified classification of dinosaur families. Edmontosaurus (ɛdˌmɒntəˈsɔrəs ed-MON-toh-SAWR-us meaning "Edmonton lizard" (after where it was found and Greek sauros meaning lizard A more detailed version can be found at List of dinosaur classifications. Dinosauria is a Clade of Archosaurs within the Phylum Chordata.

• Dinosauria

• Saurischia (theropods and sauropods)

• Herrerasaurians (early bipedal predators)
• Theropods (all bipedal; most were carnivores)

• Coelophysoids (Coelophysis and close relatives)
• Ceratosaurians (Ceratosaurus and abelisaurids - the latter were important Late Cretaceous predators in southern continents)
• Spinosauroids (long bodies, short arms, some with crocodile-like skulls and bony "sails" in their backs)
• Carnosaurians (Allosaurus and close relatives, like Carcharodontosaurus)
• Coelurosaurians (diverse, with a range of body sizes and niches)

• Tyrannosauroids (small to gigantic, often with reduced forelimbs)
• Ornithomimosaurians ("ostrich-mimics", toothless, carnivores to herbivores)
• Therizinosauroids (bipedal herbivores with long arms and small heads)
• Oviraptorosaurians (toothless; their diet and lifestyle are uncertain)
• Dromaeosaurids (like the "raptors" in Jurassic Park)
• Troodontids (similar to dromaeosaurids, but more lightly built, and possibly omnivorous)
• Birds (the only living dinosaurs)

• Sauropodomorphs (quadrupedal herbivores with small heads and long necks and tails, and elephant-like bodies)

• "Prosauropods" (early relatives of sauropods; small to quite large; some possibly omnivorous; bipeds and quadrupeds)
• Sauropods (very large, usually over 15 meters long [49 ft])

• Diplodocoids (skulls and tails elongated; teeth typically narrow and pencil-like)
• Macronarians (boxy skulls; spoon-shaped or pencil-shaped teeth)

• Brachiosaurids (very long necks; forelimbs longer than hindlimbs)
• Titanosaurians (diverse; stocky, with wide hips; most common in the Late Cretaceous of southern continents)

• Ornithischians (diverse bipedal and quadrupedal herbivores)

• Heterodontosaurids (meter- or yard-scale herbivores or omnivores with prominent canine teeth)
• Thyreophorans (armored dinosaurs, mostly quadrupeds)

• Ankylosaurians (scutes as primary armor; some had club-like tails)
• Stegosaurians (spikes and plates as primary armor)

• Ornithopods (diverse, from meter- or yard-scale bipeds to 12 meter (39 ft) animals that could moves as both bipeds and quadrupeds, evolved a method of chewing using skull flexibility and large numbers of teeth)

• Hadrosaurids ("duckbilled dinosaurs")

• Pachycephalosaurians ("bone-heads", bipeds with domed or knobby growth on skulls)
• Ceratopsians (dinosaurs with horns and frills, although most early forms had only the beginnings of these features)

Evolution and paleobiogeography

Dinosaur evolution after the Triassic follows changes in vegetation and the location of continents. Ornithischia (ɔrnɪˈθɪskiə) or Predentata is an extinct order of beaked herbivorous Dinosaurs The name ornithischia Heterodontosauridae ("different-toothed lizards" is a family of early Ornithischian Dinosaurs that have often been considered The Thyreophora ("shield bearers" often known simply as "armored dinosaurs" - Greek: θυρεος, a large oblong shield like a door and Ankylosauria is a group of Herbivorous Dinosaurs of the order Ornithischia. Known colloquially as stegosaurs the Stegosauria are a group of herbivorous Dinosaurs of the Jurassic and Early Cretaceous Periods Ornithopods (ɔrˈnɪθoʊpɒd are a group of bird-hipped Dinosaurs that started out as small Bipedal running grazers and grew in size and Hadrosaurids or duck-billed Dinosaurs are members of the family Hadrosauridae, and include Ornithopods such as Edmontosaurus Pachycephalosauria (ˌpækɨˌsɛfələˈsɔriə Greek for 'thick headed lizards' is a Clade of Ornithischian Dinosaurs Well-known genera Ceratopsia or Ceratopia (ˌsɛrəˈtɒpsiə/ /ˌsɛrəˈtoʊpiə Greek: "horned faces" is a group of herbivorous, beaked Dinosaurs In the Late Triassic and Early Jurassic, the continents were connected as the single landmass Pangaea, there was a worldwide dinosaur fauna mostly composed of coelophysoid carnivores and prosauropod herbivores. Pangaea, Pangæa or Pangea (pænˈdʒiːə from παν pan, meaning entire, and Γαῖα Gaea, meaning Earth in Coelophysoids were common Dinosaurs of the Late Triassic and Early Jurassic periods A carnivore (ˈkɑrnɪvɔər meaning 'meat eater' ( Latin carne meaning 'flesh' and vorare meaning 'to devour' is any animal with a diet consisting Prosauropoda (ˌproʊsɔˈrɒpədə or prosauropods (/proʊˈsɔroʊpɒd/ were a group of early Herbivorous Dinosaurs that lived during the Triassic Herbivory is a form of Predation in which an Organism, known as a herbivore, consumes principally Autotrophs ref name=Campbell>Campbell ^[33] Gymnosperm plants (particularly conifers), a potential food source, radiated in the Late Triassic. Gymnosperm (Gymnospermae are a group of Spermatophyte seed-bearing Plants with Ovules on the edge or blade of an open Sporophyll, which are Prosauropods did not have sophisticated mechanisms for processing food in the mouth, so must have employed other means of breaking down food farther along the digestive tract. ^[34] The general homogeneity of dinosaurian faunas continued into the Middle and Late Jurassic, where most localities had predators consisting of ceratosaurians, spinosauroids, and carnosaurians, and herbivores consisting of stegosaurian ornithischians and large sauropods. Ceratosaurs are members of a group of Theropod Dinosaurs defined as all theropods sharing a more recent common ancestry with Ceratosaurus than Spinosauroidea is a superfamily of tetanuran theropod Dinosaurs that lived from the Middle Jurassic to the Late Cretaceous period Carnosauria is a group of large Predatory Dinosaurs that lived during the Jurassic and Cretaceous periods Known colloquially as stegosaurs the Stegosauria are a group of herbivorous Dinosaurs of the Jurassic and Early Cretaceous Periods Examples of this include the Morrison Formation of North America and Tendaguru Beds of Tanzania. The Morrison Formation is a distinctive sequence of Late Jurassic Sedimentary rock that is found in the western United States which has been the most fertile source The Tendaguru beds are a fossil rich formation in Tanzania. It has been considered the richest of Late Jurassic strata in Africa. Dinosaurs in China show some differences, with specialized sinraptorid theropods and unusual, long-necked sauropods like Mamenchisaurus. Sinraptorids were a family of carnivorous Theropod Dinosaurs They tended to be large Predators some growing to sizes of 30 ft (10 Mamenchisaurus (mɑːˈmʌntʃiːˈsɔrəs mah-MUN-chee-SAW-rus, or spelling pronunciation /məˌmɛntʃiːˈsɔrəs/ was a plant-eating four-legged ^[33] Ankylosaurians and ornithopods were also becoming more common, but prosauropods had become extinct. Ankylosauria is a group of Herbivorous Dinosaurs of the order Ornithischia. Ornithopods (ɔrˈnɪθoʊpɒd are a group of bird-hipped Dinosaurs that started out as small Bipedal running grazers and grew in size and Conifers and pteridophytes were the most common plants. The pteridophytes are Vascular plants (plants with Xylem and Phloem) that neither Flower nor produce Seeds hence they are called vascular Sauropods, like the earlier prosauropods, were not oral processors, but ornithischians were evolving various means of dealing with food in the mouth, including potential cheek-like organs to keep food in the mouth, and jaw motions to grind food. Cheeks ( Latin: buccae) constitute the area of the Face below the Eyes and between the Nose and the left or right Ear ^[34] Another notable evolutionary event of the Jurassic was the appearance of true birds, descended from maniraptoran coelurosaurians. Maniraptora ("hand snatchers" is a Clade of Coelurosaurian Dinosaurs which includes the Birds and the dinosaurs that were more closely For the prehistoric gliding reptile see Coelurosauravus. Coelurosauria (sɨˌljʊərəˈsɔriə is defined as the clade containing all Theropod ^[6]

By the Early Cretaceous and the ongoing breakup of Pangaea, dinosaurs were becoming strongly differentiated by landmass. The earliest part of this time saw the spread of ankylosaurians, iguanodontians, and brachiosaurids through Europe, North America, and northern Africa. Iguanodonts were herbivorous Dinosaurs that lived from the mid- Jurassic to Late Cretaceous. Brachiosauridae are a family of Dinosaurs whose members are known as brachiosaurids. These were later supplemented or replaced in Africa by large spinosaurid and carcharodontosaurid theropods, and rebbachisaurid and titanosaurian sauropods, also found in South America. Spinosauridae is a family of unusual Theropod Dinosaurs Members of this group were large Bipedal Predators with elongated Crocodile Carcharodontosaurids (from the Greek Carcharodontosauros: "shark-toothed lizards" were a group of carnivorous Theropod Dinosaurs Rebbachisauridae is a family of Sauropod Dinosaurs known from fragmentary Fossil remains from the Cretaceous of South America Titanosaurs (members of the groups Titanosauria and/or Titanosauroidea) were a diverse group of sauropod Dinosaurs which included Saltasaurus In Asia, maniraptoran coelurosaurians like dromaeosaurids, troodontids, and oviraptorosaurians became the common theropods, and ankylosaurids and early ceratopsians like Psittacosaurus became important herbivores. Maniraptora ("hand snatchers" is a Clade of Coelurosaurian Dinosaurs which includes the Birds and the dinosaurs that were more closely For the prehistoric gliding reptile see Coelurosauravus. Coelurosauria (sɨˌljʊərəˈsɔriə is defined as the clade containing all Theropod Dromaeosauridae is a family of Bird -like Theropod Dinosaurs They were small to medium-sized feathered Carnivores that flourished in the Troodontidae is a family of Bird -like theropod Dinosaurs In previous decades troodontid fossils were few and scrappy and they have therefore Oviraptorosaurs ("egg thief lizards" are a group of feathered Maniraptoran Dinosaurs from the Cretaceous Period of what are now An ankylosaurid is a member of the Ankylosauridae family of armored dinosaurs that evolved 125 Million years ago (along with another family of Ceratopsia or Ceratopia (ˌsɛrəˈtɒpsiə/ /ˌsɛrəˈtoʊpiə Greek: "horned faces" is a group of herbivorous, beaked Dinosaurs Meanwhile, Australia was home to a fauna of basal ankylosaurians, hypsilophodonts, and iguanodontians. Hypsilophodonts (named after the Hypsilophus Genus of Iguana Lizard, literally meaning "high-crested Tooth " ^[33] The stegosaurians appear to have gone extinct at some point in the late Early Cretaceous or early Late Cretaceous. A major change in the Early Cretaceous, which would be amplified in the Late Cretaceous, was the evolution of flowering plants. The flowering plants or angiosperms ( Angiospermae or Magnoliophyta) are the most widespread group At the same time, several groups of dinosaurian herbivores evolved more sophisticated ways to orally process food. Ceratopsians developed a method of slicing with teeth stacked on each other in batteries, and iguanodontians refined a method of grinding with tooth batteries, taken to its extreme in hadrosaurids. Hadrosaurids or duck-billed Dinosaurs are members of the family Hadrosauridae, and include Ornithopods such as Edmontosaurus ^[34] Some sauropods also evolved tooth batteries, best exemplified by the rebbachisaurid Nigersaurus. Nigersaurus (meaning " Niger Lizard " is a Genus of diplodocoid Sauropod Dinosaur from the middle ^[35]

There were three general dinosaur faunas in the Late Cretaceous. In the northern continents of North America and Asia, the major theropods were tyrannosaurids and various types of smaller maniraptoran theropods, with a predominantly ornithischian herbivore assemblage of hadrosaurids, ceratopsians, ankylosaurids, and pachycephalosaurians. Tyrannosauridae (or tyrannosaurids, meaning "tyrant lizards" is a family of Coelurosaurian Theropod Dinosaurs which Pachycephalosauria (ˌpækɨˌsɛfələˈsɔriə Greek for 'thick headed lizards' is a Clade of Ornithischian Dinosaurs Well-known genera In the southern continents that had made up the now-splitting Gondwana, abelisaurids were the common theropods, and titanosaurian sauropods the common herbivores. Gondwana (ɡɒnˈdwɑːnə originally Gondwanaland) was a southern Supercontinent that existed about 500 to 200 Ma ago Abelisauridae (meaning "Abel's lizards" is a family (or Clade) of Ceratosaurian Theropod Dinosaurs Abelisaurids thrived Finally, in Europe, dromaeosaurids, rhabdodontid iguanodontians, nodosaurid ankylosaurians, and titanosaurian sauropods were prevalent. Rhabdodontids were Herbivorous Ornithopod Dinosaurs from the Late Cretaceous Period Nodosauridae is a family of Ankylosaurian Dinosaurs from the Cretaceous Period of what are now North America, Asia, ^[33] Flowering plants were greatly radiating,^[34] with the first grasses appearing by the end of the Cretaceous. ^[36] Grinding hadrosaurids and shearing ceratopsians became extremely diverse across North America and Asia. Theropods were also radiating as herbivores or omnivores, with therizinosaurians and ornithomimosaurians becoming common. Therizinosaurs (or segnosaurs) were theropod Dinosaurs and members of the Clade Therizinosauroidea Ornithomimosaurs (meaning ' Bird mimic lizards' or members of the Clade Ornithomimosauria are Theropod Dinosaurs like ^[34]

The Cretaceous–Tertiary extinction event, which occurred approximately 65 million years ago at the end of the Cretaceous period, caused the extinction of all dinosaurs except for the line that had already given rise to the first birds. The Cretaceous–Tertiary extinction event, which occurred approximately ( Ma) was a large-scale mass extinction of animal and plant species in a geologically Some other diapsid groups, such as crocodylians, lizards, snakes, sphenodontians, and choristoderans, also survived the event. Diapsids ("two arches" are a group of Reptiles that developed two holes ( Temporal fenestra) in each side of their Skulls about 300 Million Lizards are a large and widespread group of Reptiles of the order Squamata, with nearly 5000 species and ranging across all continents except A snake is an elongate Reptile of the suborder Serpentes Like all reptiles snakes are covered in scales. Sphenodontia is an order of lizard-like reptiles that includes only one living genus the Tuatara ( Sphenodon) Choristodera is an order of semi-aquatic Diapsid Reptiles which ranged from the Middle Jurassic, or possibly Late Triassic, to ^[37]

Paleobiology

Knowledge about dinosaurs is derived from a variety of fossil and non-fossil records, including fossilized bones, feces, trackways, gastroliths, feathers, impressions of skin, internal organs and soft tissues. FOSSIL is a standard protocol for allowing serial communication for Telecommunications programs under the DOS Operating system. Bones are rigid organs that form part of the Endoskeleton of Vertebrates They function to move support and protect the various organs of the body produce Feces, faeces, or fæces (see spelling differences) is a waste product from an animal's digestive tract expelled through the Anus A trackway is an ancient route of travel for people and/or animals Gastroliths (' Stomach stones' or ' Gizzard stones' are rocks, which are or have been held inside the digestive tract of an animal Feathers are one of the epidermal growths that form the distinctive outer covering or Plumage, on Birds They are considered the most complex integumentary structures In Anatomy, a viscus (ˈvɪskəs ( Plural: viscera /ˈvɪsərə/ is an internal organ of an animal (including humans in particular an internal In Medicine, the term soft tissue refers to tissues that connect support or surround other structures and organs of the body ^[38][39] Many fields of study contribute to our understanding of dinosaurs, including physics (especially biomechanics), chemistry, biology, and the earth sciences (of which paleontology is a sub-discipline). Physics (Greek Physis - φύσις in everyday terms is the Science of Matter and its motion. Biomechanics is the application of mechanical principles on living organisms Chemistry (from Egyptian kēme (chem meaning "earth") is the Science concerned with the composition structure and properties Foundations of modern biology There are five unifying principles Earth science (also known as geoscience, the geosciences or the Earth Sciences) is an all-embracing term for the Sciences related to the planet Palaeontology redirects here For the Scientific journal, see Palaeontology (journal. Two topics of particular interest and study have been dinosaur size and behavior.

Size

Main article: Dinosaur size

While the evidence is incomplete, it is clear that, as a group, dinosaurs were large. Even by dinosaur standards, the sauropods were gigantic. Sauropoda (sɔˈrɒpədə or the sauropods (/ˈsɔroʊpɒd/ are a suborder or infraorder of the Saurischian ("lizard-hipped" For much of the dinosaur era, the smallest sauropods were larger than anything else in their habitat, and the largest were an order of magnitude more massive than anything else that has since walked the Earth. An order of magnitude is the class of scale or magnitude of any amount where each class contains values of a fixed ratio to the class preceding it Giant prehistoric mammals such as the Indricotherium and the Columbian mammoth were dwarfed by the giant sauropods, and only a handful of modern aquatic animals approach or surpass them in size — most notably the blue whale, which reaches up to 173,000 kilograms (381,000 lb) and over 30 meters (100 ft) in length. Mammals ( class Mammalia) are a class of Vertebrate Animals characterized by the presence of Sweat glands, including sweat glands Paraceratherium, also commonly known as Indricotherium or Baluchitherium or just Indricothere (see taxonomic A mammoth is any Species of the Extinct Genus Mammuthus. These Proboscideans are members of the elephant family and The Blue Whale ( Balaenoptera musculus) is a Marine mammal belonging to the suborder of Baleen whales (called Mysticeti ^[40] There are several proposed advantages for the large size of sauropods, including protection from predation, reduction of energy use, and longevity, but it may be that the most important advantage was dietary. Large animals are more efficient at digestion than small animals, because food spends more time in their digestive systems. This also permits them to subsist on food with lower nutritive value than smaller animals. Sauropod remains are mostly found in rock formations interpreted as dry or seasonally dry, and the ability to eat large quantities of low nutrient browse would have been advantageous in such environments. This is a List of rock formations meaning isolated scenic or spectacular surface rock outcrops ^[41]

Most dinosaurs, however, were much smaller than the giant sauropods. Current evidence suggests that dinosaur average size varied through the Triassic, early Jurassic, late Jurassic and Cretaceous periods. ^[28] Theropod dinosaurs, when sorted by estimated weight into categories based on order of magnitude, most often fall into the 100 to 1,000 kilogram (500 to 4,500 lb) category, whereas recent predatory carnivorans peak in the 10 to 100 kilogram (50 to 450 lb) category. An order of magnitude is the class of scale or magnitude of any amount where each class contains values of a fixed ratio to the class preceding it The Holocene is a Geological epoch which began approximately 10000 years ago (about 8000 BC The diverse order Carnivora (kɑrˈnɪvərə or sometimes /ˌkɑrnɪˈvɔərə/ from Latin carō (stem carn-) "flesh" + vorāre ^[42] The mode of dinosaur body masses is between one and ten metric tonnes. In Statistics, the mode is the value that occurs the most frequently in a Data set or a Probability distribution. ^[43] This contrasts sharply with the size of Cenozoic mammals, estimated by the National Museum of Natural History as about 2 to 5 kilograms (5 to 10 lb). The Cenozoic (also Caenozoic or Cainozoic) Era (ˌsiːnəˈzoʊɪk/ /ˌsɛn- (meaning "new life" ( Greek ( kainos) "new" The National Museum of Natural History is a Natural history Museum administered by the Smithsonian Institution, located on the National ^[44]

Largest and smallest

Only a tiny percentage of animals ever fossilize, and most of these remain buried in the earth. Few of the specimens that are recovered are complete skeletons, and impressions of skin and other soft tissues are rare. Rebuilding a complete skeleton by comparing the size and morphology of bones to those of similar, better-known species is an inexact art, and reconstructing the muscles and other organs of the living animal is, at best, a process of educated guesswork. As a result, scientists will probably never be certain of the largest and smallest dinosaurs. The largest organism found on earth can be measured using a variety of methods

The tallest and heaviest dinosaur known from good skeletons is Brachiosaurus brancai (also known as Giraffatitan). Brachiosaurus (ˌbrækiəˈsɔrəs meaning "arm lizard" from the Greek brachion /βραχιων meaning "arm" and sauros Brachiosaurus (ˌbrækiəˈsɔrəs meaning "arm lizard" from the Greek brachion /βραχιων meaning "arm" and sauros Its remains were discovered in Tanzania between 1907–12. Tanzania ˌtænzəˈniːə officially the United Republic of Tanzania (Jamhuri ya Muungano wa Tanzania is a country in East Africa bordered by Kenya Bones from multiple similarly-sized individuals were incorporated into the skeleton now mounted and on display at the Humboldt Museum of Berlin;^[45] this mount is 12 meters (39 ft) tall and 22. The Museum für Naturkunde (in English, the Museum of Natural History) widely known as the Naturkundemuseum, occasionally as the Humboldt Museum Berlin is the capital city and one of sixteen states of Germany. 5 meters (74 ft) long, and would have belonged to an animal that weighed between 30,000 and 60,000 kilograms (70,000 and 130,000 lb). The longest complete dinosaur is the 27 m (89 ft) long Diplodocus, which was discovered in Wyoming in the United States and displayed in Pittsburgh's Carnegie Natural History Museum in 1907. Diplodocus (dɪˈplɒdəkəs /daɪˈplɒdəkəs/ Diplodocus is among the most easily identifiable dinosaurs with its classic dinosaur shape long neck The State of Wyoming ( is a sparsely populated state in the western region of the United States. The United States of America —commonly referred to as the This article is about an organization that operates museums For the foundation which supports scientific research refer to the Carnegie Institution of Washington.

There were larger dinosaurs, but knowledge of them is based entirely on a small number of fragmentary fossils. Most of the largest herbivorous specimens on record were all discovered in the 1970s or later, and include the massive Argentinosaurus, which may have weighed 80,000 to 100,000 kilograms (90 to 110 short tons); some of the longest, the 33. Herbivory is a form of Predation in which an Organism, known as a herbivore, consumes principally Autotrophs ref name=Campbell>Campbell Argentinosaurus (meaning " Argentina lizard" was a herbivorous Sauropod Dinosaur Genus that was among the largest 5 meters (110 ft) long Diplodocus hallorum^[41] (formerly Seismosaurus) and the 33 meters (110 ft) long Supersaurus;^[46] and the tallest, the 18 meters (59 ft) Sauroposeidon, which could have reached a sixth-floor window. Diplodocus (dɪˈplɒdəkəs /daɪˈplɒdəkəs/ Diplodocus is among the most easily identifiable dinosaurs with its classic dinosaur shape long neck Supersaurus (meaning "super lizard" is a Genus of Diplodocid Sauropod Dinosaur discovered in the Upper Jurassic Sauroposeidon (pronounced SAWR-o-po-SIE-don meaning " Earthquake - Lizard God " is a Genus of Sauropod The longest of them all may have been Amphicoelias fragillimus, known only from a now lost partial vertebral neural arch described in 1878. Amphicoelias (ˌæmfɨˈsiːliəs meaning 'doubly hollow' from the Greek amphi: "on both sides" and koilos: "hollow concave" The vertebral arch (or neural arch) is the posterior part of a Vertebra. Extrapolating from the illustration of this bone, the animal may have been 58 meters (190 ft) long and weighed over 120,000 kilograms (260,000 lb),^[41] heavier than all known dinosaurs except possibly the poorly known Bruhathkayosaurus, which could have weighed 175,000 to 220,000 kilograms (400,000 to 500,000 lb). Bruhathkayosaurus (bruːˌhæθkeɪoʊˈsɔrəs meaning 'huge bodied lizard' might have been the largest Dinosaur that ever lived The largest known carnivorous dinosaur was Spinosaurus, reaching a length of 16 to 18 meters (50 to 60 ft), and weighing in at 8,150 kilograms (18,000 lb). A carnivore (ˈkɑrnɪvɔər meaning 'meat eater' ( Latin carne meaning 'flesh' and vorare meaning 'to devour' is any animal with a diet consisting Spinosaurus (meaning "spine lizard" is a Genus of theropod Dinosaur which lived in what is now North Africa, from ^[47] Other large meat-eaters included Giganotosaurus, Mapusaurus, Tyrannosaurus rex and Carcharodontosaurus. Giganotosaurus (meaning 'giant southern lizard' derived from the Ancient Greek gigas/γίγας meaning 'giant' notos/νότος Mapusaurus ('earth lizard' was a giant Carnosaurian Dinosaur from the Late Cretaceous of what is now Argentina. Tyrannosaurus ( or, meaning 'tyrant lizard' is a Genus of Theropod Dinosaur. Carcharodontosaurus (ˌkɑrkərəˌdɒntəˈsɔːrəs was a gigantic carnivorous carcharodontosaurid Dinosaur that lived around 98 to 93

Not including modern birds, the smallest dinosaurs known were about the size of a crow or a chicken. The true crows are large Passerine Birds that comprise the Genus Corvus in the family Corvidae. The chicken ( Gallus gallus, sometimes G gallus domesticus) is a domesticated Fowl which is traditionally believed to have descended from The theropods Microraptor and Parvicursor were both under 0. Microraptor (meaning "small thief" is a Genus of small Dromaeosaurid Dinosaur. Parvicursor (meaning "small runner" is a Genus of tiny Maniraptoran Dinosaur with long slender legs for fast running 6 meters (2 ft) in length.

Behavior

Interpretations of dinosaur behavior are generally based on the pose of body fossils and their habitat, computer simulations of their biomechanics, and comparisons with modern animals in similar ecological niches. A habitat (which is Latin for "it inhabits" is an Ecological or environmental area that is inhabited by a particular Species. A computer simulation, a computer model or a computational model is a Computer program, or network of computers that attempts to simulate an Biomechanics is the application of mechanical principles on living organisms In Ecology, a niche (pronounced nich nēsh or nish A shorthand definition of niche is how an organism makes a living As such, the current understanding of dinosaur behavior relies on speculation, and will likely remain controversial for the foreseeable future. However, there is general agreement that some behaviors which are common in crocodiles and birds, dinosaurs' closest living relatives, were also common among dinosaurs.

The first direct evidence of herding behavior was the 1878 discovery of 31 Iguanodon dinosaurs which were then thought to have perished together in Bernissart, Belgium, after they fell into a deep, flooded sinkhole and drowned. A herd is a large group of animals The term is usually applied to mammals particularly Ungulates. Iguanodon (ɪˈgwɑːnədɒn or /ɪˈgwænədɒn/ meaning " Iguana Tooth " is a Genus of Ornithopod Dinosaur Bernissart is a Walloon Municipality located in the Belgian province of Hainaut. The Kingdom of Belgium is a Country in northwest Europe. It is a founding member of the European Union and hosts its headquarters as well as those A sinkhole, also known as a sink, shake hole, swallow hole, swallet, doline or Cenote, is a natural depression ^[48] Other mass death sites have been subsequently discovered. Those, along with multiple trackways, suggest that herd or pack behavior was common in many dinosaur species. A herd is a large group of animals The term is usually applied to mammals particularly Ungulates. A pack hunter is a Predator belonging to the Animal kingdom which has evolved to hunt its Prey by working together with other members of its Species Trackways of hundreds or even thousands of herbivores indicate that duck-bills (hadrosaurids) may have moved in great herds, like the American Bison or the African Springbok. Hadrosaurids or duck-billed Dinosaurs are members of the family Hadrosauridae, and include Ornithopods such as Edmontosaurus The American bison ( Bison bison) is a Bovine Mammal, also commonly known as the American buffalo. The Springbok ( Afrikaans and Dutch: spring = jump bok = Antelope or Goat) ( Antidorcas marsupialis) is a medium Sauropod tracks document that these animals traveled in groups composed of several different species, at least in Oxford, England,^[49] although there is not evidence for specific herd structures. Oxford is currently bidding for the 2010 Wikimania Conference Oxford () is a city, and the County town of Oxfordshire, ^[50] Dinosaurs may have congregated in herds for defense, for migratory purposes, or to provide protection for their young. Bird migration refers to the regular seasonal journeys undertaken by many species of Birds Bird movements include those made in response to changes in food availability The interpretation of dinosaurs as gregarious has also extended to depicting carnivorous theropods as pack hunters working together to bring down large prey. A pack hunter is a Predator belonging to the Animal kingdom which has evolved to hunt its Prey by working together with other members of its Species ^[51][52] However, this lifestyle is uncommon among the modern relatives of dinosaurs (crocodiles and other reptiles, and birds - Harris's Hawk is a well-documented exception), and the taphonomic evidence suggesting pack hunting in such theropods as Deinonychus and Allosaurus can also be interpreted as the results of fatal disputes between feeding animals, as is seen in many modern diapsid predators. A crocodile is any Species belonging to the family Crocodylidae (sometimes classified instead as the Subfamily Crocodylinae) Birds ( class Aves) are bipedal endothermic ( Warm-blooded) Vertebrate animals that lay eggs. The Harris's Hawk or Harris Hawk, Parabuteo unicinctus, formerly known as the Bay-winged Hawk or Dusky Hawk, is a medium-large Bird Taphonomy is the study of a decaying Organism over time The term taphonomy (from the Greek taphos - τάφος meaning burial and nomos - Deinonychus (daɪˈnɒnikəs ( Greek δεινος, 'terrible' and ονυξ/ονυχος, 'claw' was a Genus of carnivorous Allosaurus (ˌæləˈsɔrəs is a Genus of large Theropod Dinosaur that lived 155 to 145 million years ago in the Late Jurassic Diapsids ("two arches" are a group of Reptiles that developed two holes ( Temporal fenestra) in each side of their Skulls about 300 Million ^[53]

Jack Horner's 1978 discovery of a Maiasaura ("good mother dinosaur") nesting ground in Montana demonstrated that parental care continued long after birth among the ornithopods. John "Jack" R Horner (born June 15, 1946) is an American paleontologist who discovered and named Maiasaura Maiasaura (meaning "good mother lizard" is a large duck-billed Dinosaur Genus that lived in the area currently covered by the A nest is a place of refuge to hold an animal's eggs and/or provide a place to raise their offspring Montana ( is a state in the Western United States. One-third of the state in the western part contains numerous mountain ranges (approximately 77 named of the northern Ornithopods (ɔrˈnɪθoʊpɒd are a group of bird-hipped Dinosaurs that started out as small Bipedal running grazers and grew in size and ^[54] There is also evidence that other Cretaceous-era dinosaurs, like Patagonian titanosaurian sauropods (1997 discovery), also nested in large groups. Llao LLaojpg|thumb|250px| Lake Nahuel Huapi, near Bariloche, Argentina Titanosaurs (members of the groups Titanosauria and/or Titanosauroidea) were a diverse group of sauropod Dinosaurs which included Saltasaurus ^[55] The Mongolian oviraptorid Citipati was discovered in a chicken-like brooding position in 1993, which may mean it was covered with an insulating layer of feathers that kept the eggs warm. Mongolia (mɒŋˈɡoʊliə, literally Mongol country/nation,) is a Landlocked Country in East Oviraptoridae is a group of bird-like Maniraptoran Dinosaurs They are currently known from Mongolia and China, although there is an unpublished Citipati (ˈtʃiːt̪ipəːt̪i in Sanskrit, for 'funeral pyre lord' is a Genus of Oviraptorid Theropod Dinosaur from The chicken ( Gallus gallus, sometimes G gallus domesticus) is a domesticated Fowl which is traditionally believed to have descended from Incubation is the process by which Birds hatch their eggs, and to the development of the Embryo within the egg In most Birds and Reptiles an egg ( Latin ovum) is the Zygote, resulting from Fertilization of the Ovum. ^[56] Parental care is also implied by other finds. For example, the fossilized remains of a grouping of Psittacosaurus has been found, consisting of one adult and 34 juveniles; in this case, the large number of juveniles may be due to communal nesting. Psittacosaurus ( or, from the Greek for ' Parrot Lizard ' is a Genus of Psittacosaurid Ceratopsian ^[57] Additionally, a dinosaur embryo (pertaining to the prosauropod Massospondylus) was found without teeth, indicating that some parental care was required to feed the young dinosaur. Prosauropoda (ˌproʊsɔˈrɒpədə or prosauropods (/proʊˈsɔroʊpɒd/ were a group of early Herbivorous Dinosaurs that lived during the Triassic Massospondylus (ˌmæsoʊˈspɒndɨləs from Greek, (massōn "longer" and (spondylos "vertebra" is a Genus of prosauropod ^[58] Trackways have also confirmed parental behavior among ornithopods from the Isle of Skye in northwestern Scotland. Skye or the Isle of Skye ( Scottish Gaelic An t-Eilean Sgitheanach əɲ tʰʲelan s̪kʲiə Scotland ( Gaelic: Alba) is a Country in northwest Europethat occupies the northern third of the island of Great Britain. ^[59] Nests and eggs have been found for most major groups of dinosaurs, and it appears likely that dinosaurs communicated with their young, in a manner similar to modern birds and crocodiles.

The crests and frills of some dinosaurs, like the marginocephalians, theropods and lambeosaurines, may have been too fragile to be used for active defense, so they were likely used for sexual or aggressive displays, though little is known about dinosaur mating and territorialism. Marginocephalia ("fringed heads" is a Clade of Ornithischian Dinosaurs that includes the thick-skulled pachycephalosaurids, and horned Theropods (ˈθɪərəpɒd theropoda /θiːˈrɒpədə/ 'beast feet' are a group of Bipedal Saurischian Dinosaurs Although they were primarily Hadrosaurids or duck-billed Dinosaurs are members of the family Hadrosauridae, and include Ornithopods such as Edmontosaurus In Ethology, Sociobiology and Behavioral ecology, the term territory refers to any sociographical area that an Animal of a particular Species Head wounds from bites suggest that theropods, at least, engaged in active aggressive confrontations. ^[60] The nature of dinosaur communication also remains enigmatic, and is an active area of research. Animal communication is any Behaviour on the part of one Animal that has an effect on the current or future behaviour of another animal For example, recent studies suggest that the hollow crests of the lambeosaurines may have functioned as resonance chambers used for a wide range of vocalizations. A resonance chamber uses Resonance to amplify Sound. The chamber has interior surfaces which reflect an acoustic wave Animal communication is any Behaviour on the part of one Animal that has an effect on the current or future behaviour of another animal ^[61][62]

From a behavioral standpoint, one of the most valuable dinosaur fossils was discovered in the Gobi Desert in 1971. The Gobi (Говь Govi or Gov', "gravel-covered plain" Chinese: zh-t 戈壁(沙漠 Gēbì (Shāmò) It included a Velociraptor attacking a Protoceratops,^[63] providing evidence that dinosaurs did indeed attack each other. Velociraptor (vɨˈlɒsɨræptɚ meaning 'swift thief' 'swift plunderer' or 'swift bird of prey' is a Genus of Dromaeosaurid theropod Protoceratops (meaning 'First Horned Face' derived from Greek proto-/πρωτο- 'first' cerat-/κερατ- 'horn' ^[64] Additional evidence for attacking live prey is the partially-healed tail of an Edmontosaurus, a hadrosaurid dinosaur; the tail is damaged in such a way that shows the animal was bitten by a tyrannosaur but survived. Edmontosaurus (ɛdˌmɒntəˈsɔrəs ed-MON-toh-SAWR-us meaning "Edmonton lizard" (after where it was found and Greek sauros meaning lizard ^[64] Cannibalism amongst some species of dinosaurs was confirmed by tooth marks found in Madagascar in 2003, involving the theropod Majungasaurus. Cannibalism is the act of one individual of a species consuming all or part of another individual of the same species as food Majungasaurus (; meaning "Mahajanga lizard" is a Genus of Abelisaurid Theropod Dinosaur that lived in Madagascar ^[65]

Based on current fossil evidence from dinosaurs such as Oryctodromeus, some herbivorous species seem to have led a partially fossorial (burrowing) lifestyle,^[66] and some bird-like species may have been arboreal (tree-climbing), most notably primitive dromaeosaurids such as Microraptor^[67] and the enigmatic scansoriopterygids. Oryctodromeus (meaning "digging runner" was a Genus of small Ornithopod Dinosaur, the fossilized remains of which have been found A fossorial is an Organism adapted to digging and life underground such as the Badger, the Naked mole rat, and the mole salamanders Ambystomatidae Arboreal is a word meaning "related to or resembling trees" Dromaeosauridae is a family of Bird -like Theropod Dinosaurs They were small to medium-sized feathered Carnivores that flourished in the Microraptor (meaning "small thief" is a Genus of small Dromaeosaurid Dinosaur. Scansoriopterygidae (meaning "climbing wings" may be a family of maniraptoran Dinosaurs known from well-preserved Fossils uncovered in Liaoning ^[68] However, most dinosaurs seem to have relied on land-based locomotion. A good understanding of how dinosaurs moved on the ground is key to models of dinosaur behavior; the science of biomechanics, in particular, has provided significant insight in this area. Biomechanics is the application of mechanical principles on living organisms For example, studies of the forces exerted by muscles and gravity on dinosaurs' skeletal structure have investigated how fast dinosaurs could run,^[69] whether diplodocids could create sonic booms via whip-like tail snapping,^[70] and whether sauropods could float. Diplodocids, or members of the family Diplodocidae ("double beams" are a group of Sauropod Dinosaurs The family includes some of the longest The term sonic boom is commonly used to refer to the shocks caused by the Supersonic flight of an aircraft The word whip describes two basic types of tools A long stick-like device usually slightly flexible with a small bit of leather or cord called a "popper" on the ^[71]

Physiology

Main article: Physiology of dinosaurs

A vigorous debate on the subject of temperature regulation in dinosaurs has been ongoing since the 1960s. Originally, scientists broadly disagreed as to whether dinosaurs were capable of regulating their body temperatures at all. More recently, dinosaur endotherm has become the consensus view, and debate has focused on the mechanisms of temperature regulation. In Biology, a warm-blooded Animal species is one whose members maintain thermal Homeostasis; that is they keep their body temperature at a roughly constant

After dinosaurs were discovered, paleontologists first posited that they were ectothermic creatures: "terrible lizards" as their name suggests. Cold-blooded organisms (called poikilotherms - "of varying temperature" maintain their body temperatures in ways different from Mammals and Birds Lizards are a large and widespread group of Reptiles of the order Squamata, with nearly 5000 species and ranging across all continents except This supposed cold-bloodedness implied that dinosaurs were relatively slow, sluggish organisms, comparable to modern reptiles, which need external sources of heat in order to regulate their body temperature. Dinosaur ectothermy remained a prevalent view until Robert T. "Bob" Bakker, an early proponent of dinosaur endothermy, published an influential paper on the topic in 1968. Robert T Bakker (born March 24, 1945, in Bergen County New Jersey) is an American Paleontologist who helped reshape modern theories about

Modern evidence indicates that dinosaurs thrived in cooler temperate climates, and that at least some dinosaur species must have regulated their body temperature by internal biological means (perhaps aided by the animals' bulk). Evidence of endotherm in dinosaurs includes the discovery of polar dinosaurs in Australia and Antarctica (where they would have experienced a cold, dark six-month winter), the discovery of dinosaurs whose feathers may have provided regulatory insulation, and analysis of blood-vessel structures that are typical of endotherms within dinosaur bone. In Biology, a warm-blooded Animal species is one whose members maintain thermal Homeostasis; that is they keep their body temperature at a roughly constant Skeletal structures suggest that theropods and other dinosaurs had active lifestyles better suited to an endothermic cardiovascular system, while sauropods exhibit fewer endothermic characteristics. It is certainly possible that some dinosaurs were endothermic while others were not. Scientific debate over the specifics continues. ^[72]

Complicating the debate is the fact that warm-bloodedness can emerge based on more than one mechanism. Most discussions of dinosaur endothermy tend to compare them to average birds or mammals, which expend energy to elevate body temperature above that of the environment. Small birds and mammals also possess insulation, such as fat, fur, or feathers, which slows down heat loss. The term thermal insulation can refer to materials used to reduce the rate of Heat transfer, or the methods and processes used to reduce heat transfer Fats consist of a wide group of compounds that are generally soluble in organic solvents and largely insoluble in water Fur is a body hair of any non-human Mammal, also known as the Pelage. Feathers are one of the epidermal growths that form the distinctive outer covering or Plumage, on Birds They are considered the most complex integumentary structures However, large mammals, such as elephants, face a different problem because of their relatively small ratio of surface area to volume (Haldane's principle). John Burdon Sanderson Haldane FRS ( 5 November 1892 &ndash 1 December 1964) known as Jack (but who used 'J This ratio compares the volume of an animal with the area of its skin: as an animal gets bigger, its surface area increases more slowly than its volume. At a certain point, the amount of heat radiated away through the skin drops below the amount of heat produced inside the body, forcing animals to use additional methods to avoid overheating. In the case of elephants, they are hairless, and have large ears which increase their surface area, and have behavioral adaptations as well (such as using the trunk to spray water on themselves and mud wallowing). These behaviors increase cooling through evaporation.

Large dinosaurs would presumably have had to deal with similar issues; their body size suggest they lost heat relatively slowly to the surrounding air, and so could have been what are called inertial homeotherms, animals that are warmer than their environments through sheer size rather than through special adaptations like those of birds or mammals. Gigantothermy is a phenomenon with significance in Biology and Paleontology, whereby large bulky ectothermic (cold-blooded animals are more easily able However, so far this theory fails to account for the numerous dog- and goat-sized dinosaur species, or the young of larger species.

Modern computerized tomography (CT) scans of a dinosaur's chest cavity (conducted in 2000) found the apparent remnants of a four-chambered heart, much like those found in today's mammals and birds. Computed tomography (CT is a Medical imaging method employing Tomography. Thescelosaurus (ˌθɛsɪləˈsɔrəs from the Greek θεσκελο-/ thescelo- meaning "godlike" "marvelous" or "wondrous" ^[73] The idea is controversial within the scientific community, coming under fire for bad anatomical science^[74] or simply wishful thinking. ^[75] The question of how this find reflects on metabolic rate and dinosaur internal anatomy may be moot, though, regardless of the object's identity: both modern crocodilians and birds, the closest living relatives of dinosaurs, have four-chambered hearts (albeit modified in crocodilians), so dinosaurs probably had them as well. Crocodilia is an order of large Reptiles that appeared about 84 million years ago in the late Cretaceous Period ( Campanian stage Birds ( class Aves) are bipedal endothermic ( Warm-blooded) Vertebrate animals that lay eggs. ^[76]

Soft tissue and DNA

One of the best examples of soft tissue impressions in a fossil dinosaur was discovered in Petraroia, Italy. Italy (Italia officially the Italian Republic, (Repubblica Italiana is located on the Italian Peninsula in Southern Europe, and on the two largest The discovery was reported in 1998, and described the specimen of a small, very young coelurosaur, Scipionyx samniticus. For the prehistoric gliding reptile see Coelurosauravus. Coelurosauria (sɨˌljʊərəˈsɔriə is defined as the clade containing all Theropod Scipionyx is a very small Genus of Theropod Dinosaur from the Early Cretaceous of Italy, around 113 million years The fossil includes portions of the intestines, colon, liver, muscles, and windpipe of this immature dinosaur. ^[38]

In the March 2005 issue of Science, Dr. Mary Higby Schweitzer and her team announced the discovery of flexible material resembling actual soft tissue inside a 68-million-year-old Tyrannosaurus rex leg bone from the Hell Creek Formation in Montana. Science is the Academic journal of the American Association for the Advancement of Science and is considered one of the world's most prestigious Scientific Mary Higby Schweitzer is a Paleontologist at North Carolina State University known for leading the groups which discovered the remains of blood cells in dinosaur Tyrannosaurus ( or, meaning 'tyrant lizard' is a Genus of Theropod Dinosaur. Bones are rigid organs that form part of the Endoskeleton of Vertebrates They function to move support and protect the various organs of the body produce The Hell Creek Formation is an intensely-studied division of Upper Cretaceous to lower Paleocene rocks in North America named for exposures studied along Hell Montana ( is a state in the Western United States. One-third of the state in the western part contains numerous mountain ranges (approximately 77 named of the northern After recovery, the tissue was rehydrated by the science team. ^[39]

When the fossilized bone was treated over several weeks to remove mineral content from the fossilized bone marrow cavity (a process called demineralization), Schweitzer found evidence of intact structures such as blood vessels, bone matrix, and connective tissue (bone fibers). The blood vessels are part of the Circulatory system and function to transport Blood throughout the body Scrutiny under the microscope further revealed that the putative dinosaur soft tissue had retained fine structures (microstructures) even at the cellular level. The exact nature and composition of this material, and the implications of Dr. Schweitzer's discovery, are not yet clear; study and interpretation of the material is ongoing. ^[39]

The successful extraction of ancient DNA from dinosaur fossils has been reported on two separate occasions, but upon further inspection and peer review, neither of these reports could be confirmed. Peer review (also known as refereeing) is the process of subjecting an author's scholarly work research or Ideas to the scrutiny of others who are ^[77] However, a functional visual peptide of a theoretical dinosaur has been inferred using analytical phylogenetic reconstruction methods on gene sequences of related modern species such as reptiles and birds. Peptides (from the Greek πεπτίδια, "small digestibles" are short Polymers formed from the linking in a defined order of α- Amino ^[78] In addition, several proteins have putatively been detected in dinosaur fossils,^[79] including hemoglobin. Proteins are large Organic compounds made of Amino acids arranged in a linear chain and joined together by Peptide bonds between the Carboxyl ^[80]

Even if dinosaur DNA could be reconstructed, it would be exceedingly difficult to clone and "grow" dinosaurs using current technology since no closely related species exist to provide zygotes or a suitable environment for embryonic development. For other meanings see Zygote (disambiguation. A zygote (from Greek ζυγωτός zugōtos "joined" or "yoked" Embryogenesis is the process by which the Embryo is formed and develops

Feathers and the origin of birds

Main article: Origin of birds

The possibility that dinosaurs were the ancestors of birds was first suggested in 1868 by Thomas Henry Huxley. The origin of birds has been a contentious topic within Evolutionary biology for many years but more recently a scientific consensus has emerged which holds that Birds Thomas Henry Huxley PC FRS (4 May 1825 – 29 June 1895 was an English Biologist, known as "Darwin's Bulldog" for his advocacy ^[81] After the work of Gerhard Heilmann in the early 20th century, the theory of birds as dinosaur descendants was abandoned in favor of generalized thecodont ancestors, with the key piece of evidence being the supposed lack of clavicles in dinosaurs. Gerhard Heilmann (1859–1946 was a Danish artist paleontologist and writer of the Origin of Birds, an influential account of bird evolution Thecodont ("socket-toothed" reptile now considered an obsolete term was formerly used to describe a diverse range of early Archosaurs that first appeared in the ^[82] However, as later discoveries showed, clavicles (or a single fused wishbone, which derived from separate clavicles) were not actually absent;^[6] they had been found as early as 1924 in Oviraptor, but misidentified as an interclavicle. The furcula (" little fork " in Latin is a forked Bone found in Birds and Theropod Dinosaurs formed by the fusion of the two An interclavicle is a bone which in most Tetrapods, is located between the Clavicles. ^[83] In the 1970s, John Ostrom revived the dinosaur-bird theory,^[84] which gained momentum in the coming decades with the advent of cladistic analysis,^[85] and a great increase in the discovery of small theropods and early birds. John H Ostrom ( February 18, 1928 &ndash July 16, 2005) was an American Paleontologist who revolutionized modern ^[15] Of particular note has been the fossils of the Yixian Formation, where a variety of theropods and early birds have been found, often with feathers of some type. The Yixian Formation is a Geological formation in Jinzhou, Liaoning, People's Republic of China, that stems from the Early Cretaceous ^[6] Birds share over a hundred distinct anatomical features with theropod dinosaurs, which are now generally accepted to have been their closest ancient relatives. ^[86] They are most closely allied with maniraptoran coelurosaurs. Maniraptora ("hand snatchers" is a Clade of Coelurosaurian Dinosaurs which includes the Birds and the dinosaurs that were more closely ^[6] A minority of scientists, most notably Alan Feduccia and Larry Martin, have proposed other evolutionary paths, including revised versions of Heilmann's basal archosaur proposal,^[87] or that maniraptoran theropods are the ancestors of birds but themselves are not dinosaurs, only convergent with dinosaurs. Alan Feduccia is a paleornithologist, specializing in the origins and Phylogeny of Birds He is the S Larry Martin (born 1943 is an American vertebrate Paleontologist and Curator of the Natural History Museum and Biodiversity Research Center at the University Convergent evolution describes the acquisition of the same biological trait in unrelated lineages ^[88]

Feathers

Main article: Feathered dinosaurs

Archaeopteryx, the first good example of a "feathered dinosaur", was discovered in 1861. Archaeopteryx, sometimes referred to by its German name Urvogel ("original bird" or "first bird" is the earliest and most primitive Bird The initial specimen was found in the Solnhofen limestone in southern Germany, which is a lagerstätte, a rare and remarkable geological formation known for its superbly detailed fossils. The Solnhofen limestone is a Jurassic Konservat-Lagerstätte that preserves a rare assemblage of Fossilized organisms some of which such as sea jellies A Lagerstätte ( German; literally place of storage; plural Lagerstätten) is a sedimentary deposit that exhibits extraordinary fossil Archaeopteryx is a transitional fossil, with features clearly intermediate between those of modern reptiles and birds. Transitional fossils are the Fossilized remains of transitional forms of life that illustrate an evolutionary transition Brought to light just two years after Darwin's seminal The Origin of Species, its discovery spurred the nascent debate between proponents of evolutionary biology and creationism. Charles Darwin 's On the Origin of Species (published 24 November 1859) is a seminal work in Scientific literature and arguably the Evolutionary biology is a sub-field of Biology concerned with the origin of Species from a Common descent, and Descent of species "Creationism" can also refer to Creation myths in general or to a concept about the origin of the soul. This early bird is so dinosaur-like that, without a clear impression of feathers in the surrounding rock, at least one specimen was mistaken for Compsognathus. Compsognathus ( Greek kompsos/κομψος; "elegant" "refined" or "dainty" and gnathos/γναθος; "jaw" ^[89]

Since the 1990s, a number of additional feathered dinosaurs have been found, providing even stronger evidence of the close relationship between dinosaurs and modern birds. The realization that Dinosaurs are closely related to Birds raised the obvious possibility of feathered dinosaurs. Most of these specimens were unearthed in the lagerstätte of the Yixian Formation, Liaoning, northeastern China, which was part of an island continent during the Cretaceous. A Lagerstätte ( German; literally place of storage; plural Lagerstätten) is a sedimentary deposit that exhibits extraordinary fossil ( is a northeastern province of the People's Republic of China. China ( Wade-Giles ( Mandarin) Chung¹kuo² is a cultural region, an ancient Civilization, and depending on perspective a National Though feathers have been found only in a few locations, it is possible that non-avian dinosaurs elsewhere in the world were also feathered. The lack of widespread fossil evidence for feathered non-avian dinosaurs may be due to the fact that delicate features like skin and feathers are not often preserved by fossilization and thus are absent from the fossil record. FOSSIL is a standard protocol for allowing serial communication for Telecommunications programs under the DOS Operating system. To this point, protofeathers (thin, filament-like structures) are known from dinosaurs at the base of Coelurosauria, such as compsognathids like Sinosauropteryx and tyrannosauroids (Dilong),^[90] but barbed feathers are only known among the coelurosaur subgroup Maniraptora, which includes oviraptorosaurs, troodontids, dromaeosaurids, and birds. Compsognathidae is a family of small carnivorous Dinosaurs generally conservative in form from the Jurassic and Cretaceous Periods Sinosauropteryx (meaning "Chinese lizard-wing" is the first and most primitive Genus of Dinosaur found with the fossilized impressions of Tyrannosauroidea (meaning 'tyrant lizard forms' is a Superfamily (or Clade) of Coelurosaurian Theropod Dinosaurs that includes Dilong (which means 'emperor dragon' is a Genus of small tyrannosauroid Dinosaur. ^[6][91] The description of feathered dinosaurs has not been without controversy; perhaps the most vocal critics have been Alan Feduccia and Theagarten Lingham-Soliar, who have proposed that protofeathers are the result of the decomposition of collagenous fiber that underlaid the dinosaurs' integument,^[92][93][94] and that maniraptoran dinosaurs with barbed feathers were not actually dinosaurs, but convergent with dinosaurs. Convergent evolution describes the acquisition of the same biological trait in unrelated lineages ^[88][93] However, their views have for the most part not been accepted by other researchers, to the point that the question of the scientific nature of Feduccia's proposals has been raised. ^[95]

Skeleton

Because feathers are often associated with birds, feathered dinosaurs are often touted as the missing link between birds and dinosaurs. Transitional fossils are the Fossilized remains of transitional forms of life that illustrate an evolutionary transition However, the multiple skeletal features also shared by the two groups represent another important line of evidence for paleontologists. Palaeontology redirects here For the Scientific journal, see Palaeontology (journal. Areas of the skeleton with important similarities include the neck, pubis, wrist (semi-lunate carpal), arm and pectoral girdle, furcula (wishbone), and breast bone. For the bone in many mammals often called the penis bone see Baculum The android pubic bone is the Ventral and Anterior In Human anatomy, the wrist is the flexible and narrower connection between the Forearm and the palm. In Tetrapods the carpus is the sole cluster of the Bones in the Wrist between the radius and Ulna and the Metacarpus The pectoral girdle is the set of bones which connect the upper limb to the axial skeleton on each side A keel in Bird anatomy is an extension of the Sternum which runs axially along the midline of the sternum and extends outward perpendicular to the plane of the Comparison of bird and dinosaur skeletons through cladistic analysis strengthens the case for the link. Cladistics is the hierarchical classification of Species based on evolutionary ancestry

Soft anatomy

Large meat-eating dinosaurs had a complex system of air sacs similar to those found in modern birds, according to an investigation which was led by Patrick O'Connor of Ohio University. Ohio University is a public university located in Athens Ohio that is situated on a 1800 acre (7 The lungs of theropod dinosaurs (carnivores that walked on two legs and had birdlike feet) likely pumped air into hollow sacs in their skeletons, as is the case in birds. In Biology, the skeleton is a strong and often a rigid framework that supports the body of an animal holding it upright and giving it shape and strength (Also skeletal "What was once formally considered unique to birds was present in some form in the ancestors of birds", O'Connor said. ^[96]

Another piece of evidence that birds and dinosaurs are closely related is the use of gizzard stones. The gizzard, also referred to as the ventriculus, gastric mill, and gigerium, is an organ in the digestive tract found in Birds Reptiles These stones are swallowed by animals to aid digestion and break down food and hard fibres once they enter the stomach. When found in association with fossils, gizzard stones are called gastroliths. FOSSIL is a standard protocol for allowing serial communication for Telecommunications programs under the DOS Operating system. Gastroliths (' Stomach stones' or ' Gizzard stones' are rocks, which are or have been held inside the digestive tract of an animal ^[97]

Reproductive biology

A discovery of features in a Tyrannosaurus rex skeleton recently provided more evidence that dinosaurs and birds evolved from a common ancestor and, for the first time, allowed paleontologists to establish the sex of a dinosaur. Tyrannosaurus ( or, meaning 'tyrant lizard' is a Genus of Theropod Dinosaur. In Biology, the skeleton is a strong and often a rigid framework that supports the body of an animal holding it upright and giving it shape and strength (Also skeletal When laying eggs, female birds grow a special type of bone in their limbs between the hard outer bone and the marrow. This medullary bone, which is rich in calcium, is used to make eggshells. Calcium (ˈkælsiəm is the Chemical element with the symbol Ca and Atomic number 20 The presence of endosteally-derived bone tissues lining the interior marrow cavities of portions of the Tyrannosaurus rex specimen's hind limb suggested that T. rex used similar reproductive strategies, and revealed the specimen to be female. ^[98] Further research has found medullary bone in the theropod Allosaurus and ornithopod Tenontosaurus. Allosaurus (ˌæləˈsɔrəs is a Genus of large Theropod Dinosaur that lived 155 to 145 million years ago in the Late Jurassic Tenontosaurus (tɨˌnɒntəˈsɔrəs ten-ON-toe-SORE-us is a Genus of medium- to large-sized Ornithopod Dinosaur. Because the line of dinosaurs that includes Allosaurus and Tyrannosaurus diverged from the line that led to Tenontosaurus very early in the evolution of dinosaurs, this suggests that dinosaurs in general produced medullary tissue. Medullary bone has been found in specimens of sub-adult size, which suggests that dinosaurs reached sexual maturity rather quickly for such large animals. ^[99]

Behavioral evidence

A recently discovered troodont fossil demonstrates that some dinosaurs slept like certain modern birds, with their heads tucked under their arms. Troodontidae is a family of Bird -like theropod Dinosaurs In previous decades troodontid fossils were few and scrappy and they have therefore ^[100] This behavior, which may have helped to keep the head warm, is also characteristic of modern birds.

Extinction

Main article: Cretaceous–Tertiary extinction event

Main article: K–T boundary

Non-avian dinosaurs suddenly became extinct approximately 65 million years ago. The Cretaceous–Tertiary extinction event, which occurred approximately ( Ma) was a large-scale mass extinction of animal and plant species in a geologically The K-T boundary is a geological signature usually a thin band dated to 65 In Biology and Ecology, extinction is the cessation of existence of a Species or group of taxa. Many other groups of animals also became extinct at this time, including ammonites (nautilus-like mollusks), mosasaurs, plesiosaurs, pterosaurs, herbivorous turtles and crocodiles, most birds, and many groups of mammals. Ammonites are an extinct group of marine animals of the subclass Ammonoidea in the class Cephalopoda phylum Nautilus (from Greek ναυτίλος, 'sailor' is the common name of any marine creatures of the Cephalopod family Nautilidae, the sole Molluscs are animals belonging to the phylum Mollusca. There are around 250000 extant Species within the phylum with an estimated 70000 Mosasaurs (from Latin Mosa meaning the ' Meuse river ' in the Netherlands and Greek sauros meaning 'lizard' were serpentine marine Turtles are Reptiles of the Order Testudines (all living turtles belong to the Crown group Chelonia) most of A crocodile is any Species belonging to the family Crocodylidae (sometimes classified instead as the Subfamily Crocodylinae) ^[13] This mass extinction is known as the Cretaceous–Tertiary extinction event. An extinction event (also known as mass extinction; extinction-level event, ELE is a sharp decrease in the number of Species in a relatively short period The Cretaceous–Tertiary extinction event, which occurred approximately ( Ma) was a large-scale mass extinction of animal and plant species in a geologically The nature of the event that caused this mass extinction has been extensively studied since the 1970s; at present, several related theories are supported by paleontologists. Though the general consensus is that an impact event was the primary cause of dinosaur extinction, some scientists cite other possible causes, or support the idea that a confluence of several factors was responsible for the sudden disappearance of dinosaurs from the fossil record.

At the peak of the Mesozoic, there were no polar ice caps, and sea levels are estimated to have been from 100 to 250 meters (300 to 800 ft) higher than they are today. A polar ice cap is a high- Latitude region of a Planet or moon that is covered in Ice. The planet's temperature was also much more uniform, with only 25 °C (45 °F) separating average polar temperatures from those at the equator. The Celsius Temperature scale was previously known as the centigrade scale. Fahrenheit is a temperature scale named after Daniel Gabriel Fahrenheit (1686–1736 a German Physicist who proposed it in 1724 On average, atmospheric temperatures were also much warmer; the poles, for example, were 50 °C (90 °F) warmer than today. ^[101][102]

The atmosphere's composition during the Mesozoic was vastly different as well. Carbon dioxide levels were up to 12 times higher than today's levels, and oxygen formed 32 to 35% of the atmosphere, as compared to 21% today. However, by the late Cretaceous, the environment was changing dramatically. Volcanic activity was decreasing, which led to a cooling trend as levels of atmospheric carbon dioxide dropped. Oxygen levels in the atmosphere also started to fluctuate and would ultimately fall considerably. Some scientists hypothesize that climate change, combined with lower oxygen levels, might have led directly to the demise of many species. If the dinosaurs had respiratory systems similar to those commonly found in modern birds, it may have been particularly difficult for them to cope with reduced respiratory efficiency, given the enormous oxygen demands of their very large bodies. ^[13]

Impact event

The asteroid collision theory, which was brought to wide attention in 1980 by Walter Alvarez and colleagues, links the extinction event at the end of the Cretaceous period to a bolide impact approximately 65. For his grandfather the American doctor see Walter C Alvarez. An extinction event (also known as mass extinction; extinction-level event, ELE is a sharp decrease in the number of Species in a relatively short period 5 million years ago. Alvarez et al. proposed that a sudden increase in iridium levels, recorded around the world in the period's rock stratum, was direct evidence of the impact. Iridium (ɪˈrɪdiəm is a Chemical element that has the symbol Ir and Atomic number 77 ^[103] The bulk of the evidence now suggests that a 5 to 15 kilometer (3 to 9 mi) wide bolide hit in the vicinity of the Yucatán Peninsula, creating the 170 kilometers (110 mi) wide Chicxulub Crater and triggering the mass extinction. The Yucatán Peninsula, in Southeastern Mexico, separates the Caribbean Sea from the Gulf of Mexico. The Chicxulub Crater (tʃikʃuˈlub is an ancient Impact crater buried underneath the Yucatán Peninsula in Mexico. An extinction event (also known as mass extinction; extinction-level event, ELE is a sharp decrease in the number of Species in a relatively short period ^[104] Scientists are not certain whether dinosaurs were thriving or declining before the impact event. Some scientists propose that the meteorite caused a long and unnatural drop in Earth's atmospheric temperature, while others claim that it would have instead created an unusual heat wave.

Although the speed of extinction cannot be deduced from the fossil record alone, various models suggest that the extinction was extremely rapid. The consensus among scientists who support this theory is that the impact caused extinctions both directly (by heat from the meteorite impact) and also indirectly (via a worldwide cooling brought about when matter ejected from the impact crater reflected thermal radiation from the sun).

In September of 2007, U. S. researchers led by William Bottke of the Southwest Research Institute in Boulder, Colorado, and Czech scientists used computer simulations to identify the probable source of the Chicxulub impact. Southwest Research Institute ( SwRI) headquartered in San Antonio Texas, is one of the oldest and largest independent Nonprofit, applied Research Boulder is a Home Rule Municipality that is the County seat and most populous city of Boulder County, Colorado, in the United States The Czech Republic ( ˈt͡ʃɛskaː ˈrɛpuˌblɪka short form in Česko ˈt͡ʃɛskɔ also called Czechia, A computer is a Machine that manipulates data according to a list of instructions. They calculated a 90% probability that a giant asteroid named Baptistina, approximately 160 kilometers (100 mi) in diameter, orbiting in the asteroid belt which lies between Mars and Jupiter, was struck by a smaller unnamed asteroid about 55 kilometers (35 mi) in diameter about 160 million years ago. 298 Baptistina is a typical Main belt Asteroid. It was discovered by Auguste Charlois on September 9, 1890 in Nice The impact shattered Baptistina, creating a cluster which still exists today as the Baptistina family. The Baptistina family is an Asteroid family that was likely produced by the breakup of an Asteroid 170 km (110 miles across 160 million years ago following an impact Calculations indicate that some of the fragments were sent hurtling into earth-crossing orbits, one of which was the 10 kilometers (6 mi) wide meteorite which struck Mexico's Yucatan peninsula 65 million years ago, creating the Chicxulub crater (175 kilometers (110 mi)). A meteorite is a natural object originating in Outer space that survives an impact with the Earth 's surface The United Mexican States ( or commonly Mexico (ˈmɛksɪkoʊ () is a federal constitutional Republic in North America. Yucatán is one of the 31 states of Mexico, located on the north of the Yucatán Peninsula. A peninsula is a piece of land that is nearly surrounded by Water but connected to Mainland via an Isthmus. The Chicxulub Crater (tʃikʃuˈlub is an ancient Impact crater buried underneath the Yucatán Peninsula in Mexico. ^[105]

While similar to Alvarez's impact theory (which involved a single asteroid or comet), this theory proposes that "passages of the solar companion star Nemesis through the Oort comet cloud would trigger comet showers. The Oort cloud ( ort alternatively the Öpik-Oort Cloud) is a hypothetical spherical cloud of Comets believed to lie roughly 50 000 AU, The Oort cloud ( ort alternatively the Öpik-Oort Cloud) is a hypothetical spherical cloud of Comets believed to lie roughly 50 000 AU, "^[106] One or more of these objects then collided with the Earth at approximately the same time, causing the worldwide extinction. As with the impact of a single asteroid, the end result of this comet bombardment would have been a sudden drop in global temperatures, followed by a protracted cool period. ^[106]

Deccan Traps

Main article: Deccan Traps

Before 2000, arguments that the Deccan Traps flood basalts caused the extinction were usually linked to the view that the extinction was gradual, as the flood basalt events were thought to have started around 68 mya and lasted for over 2 million years. The Deccan Traps are a Large igneous province located on the Deccan Plateau of west-central India (between 17-24N 73-74E and one of the largest Volcanic The Deccan Traps are a Large igneous province located on the Deccan Plateau of west-central India (between 17-24N 73-74E and one of the largest Volcanic A flood basalt or trap basalt is the result of a giant Volcanic eruption or series of Eruptions that coats large stretches of land or the Ocean floor However, there is evidence that two-thirds of the Deccan Traps were created in 1 million years about 65. 5 mya, so these eruptions would have caused a fairly rapid extinction, possibly a period of thousands of years, but still a longer period than what would be expected from a single impact event. ^[107][108]

The Deccan Traps could have caused extinction through several mechanisms, including the release of dust and sulphuric aerosols into the air which might have blocked sunlight and thereby reducing photosynthesis in plants. In addition, Deccan Trap volcanism might have resulted in carbon dioxide emissions which would have increased the greenhouse effect when the dust and aerosols cleared from the atmosphere. The Greenhouse effect refers to the change in the Thermal equilibrium temperature of a planet or moon by the presence of an Atmosphere containing gas that absorbs ^[108] Before the mass extinction of the dinosaurs, the release of volcanic gasses during the formation of the Deccan traps "contributed to an apparently massive global warming. Volcanic gases include a variety of substances given off by active (or at times by dormant Volcanoes These include gases trapped in cavities ( Vesicles) in The Deccan Traps are a Large igneous province located on the Deccan Plateau of west-central India (between 17-24N 73-74E and one of the largest Volcanic Global warming is the increase in the average measured temperature of the Some data point to an average rise in temperature of 8 °C (14 °F) in the last half million years before the impact [at Chicxulub]. The Chicxulub Crater (tʃikʃuˈlub is an ancient Impact crater buried underneath the Yucatán Peninsula in Mexico. "^[107][108]

In the years when the Deccan Traps theory was linked to a slower extinction, Luis Alvarez (who died in 1988) replied that paleontologists were being misled by sparse data. Luis W Alvarez (June 13 1911 San Francisco California &ndash September 1 1988 was an American physicist and Inventor, who spent nearly Palaeontology redirects here For the Scientific journal, see Palaeontology (journal. The Signor-Lipps effect is a Paleontological principle proposed by Philip W While his assertion was not initially well-received, later intensive field studies of fossil beds lent weight to his claim. Eventually, most paleontologists began to accept the idea that the mass extinctions at the end of the Cretaceous were largely or at least partly due to a massive Earth impact. However, even Walter Alvarez has acknowledged that there were other major changes on Earth even before the impact, such as a drop in sea level and massive volcanic eruptions that produced the Indian Deccan Traps, and these may have contributed to the extinctions. Mean sea level (MSL is the average (mean height of the Sea, with reference to a suitable reference surface ^[109]

Possible Paleocene survivors

Nonavian dinosaur remains are occasionally found above the K-T boundary. In 2002, paleontologists Zielinski and Budahn reported the discovery of a single hadrosaur leg bone fossil in the San Juan Basin, New Mexico and described it as evidence of Paleocene dinosaurs. Hadrosaurids or duck-billed Dinosaurs are members of the family Hadrosauridae, and include Ornithopods such as Edmontosaurus Paleocene Dinosaurs describe families or genera of non- avian dinosaurs that may have survived the Cretaceous–Tertiary extinction event 65 The formation in which the bone was discovered has been dated to the early Paleocene epoch approximately 64. The Paleocene or Palaeocene, "early dawn of the recent" is a geologic epoch that lasted from 65 5 million years ago. If the bone was not re-deposited into that stratum by weathering action, it would provide evidence that some dinosaur populations may have survived at least a half million years into the Cenozoic Era. In Geology and related fields a stratum (plural strata) is a layer of rock or Soil with internally consistent characteristics that distinguishes ^[110] Other evidence includes the finding of dinosaur remains in the Hell Creek Formation up to 1. The Hell Creek Formation is an intensely-studied division of Upper Cretaceous to lower Paleocene rocks in North America named for exposures studied along Hell 3 meters (51 in) above (40,000 years later than) the K-T boundary. Similar reports have come from other parts of the world, including China. ^[111] Many scientists, however, dismiss the "Paleocene dinosaurs" as re-worked, i. e. washed out of their original locations and then re-buried in much later sediments,^[112][113] or find that, if correct, the presence of a handful of dinosaurs in the early Paleocene would not change the underlying facts of the extinction. ^[112]

History of discovery

Dinosaur fossils have been known for millennia, although their true nature was not recognized. The Chinese, whose modern word for dinosaur is konglong (恐龍, or "terrible dragon"), considered them to be dragon bones and documented them as such. The Chinese Dragon or Oriental dragon is a mythical creature in East Asian culture with a Chinese origin Bones are rigid organs that form part of the Endoskeleton of Vertebrates They function to move support and protect the various organs of the body produce For example, Hua Yang Guo Zhi, a book written by Zhang Qu during the Western Jin Dynasty, reported the discovery of dragon bones at Wucheng in Sichuan Province. The Jìn Dynasty ( 265 – 420) one of the Six Dynasties, followed the Three Kingdoms period and preceded the Southern and Northern Dynasties ( Postal map spelling: Szechwan and Szechuan) is a province in western China with its capital in Chengdu. ^[114] Villagers in central China have been digging up dinosaur bones for decades, thinking they were from dragons, to make traditional medicine. ^[115] In Europe, dinosaur fossils were generally believed to be the remains of giants and other creatures killed by the Great Flood. The Mythology and Legends of many different Cultures include monsters of human appearance but prodigious size and strength The story of a Great Flood (also known as the Deluge) sent by a Deity or deities to destroy Civilization as an act of Divine retribution is a

Megalosaurus was the first dinosaur to be formally described, in 1677, when part of a bone was recovered from a limestone quarry at Cornwell near Chipping Norton, Oxfordshire, England. Megalosaurus (meaning "Great Lizard" from Greek, μεγαλο-/megalo- meaning 'big' 'tall' or 'great' and σαυρος/sauros Limestone is a Sedimentary rock composed largely of the Mineral Calcite ( Calcium carbonate: CaCO3 A quarry is a type of open-pit mine from which rock or Minerals are extracted Chipping Norton is a Town in the West Oxfordshire Distrcit of Oxfordshire, England, located north west of Oxford. History See also History of Oxfordshire The county of Oxfordshire was formed in the early years of the 10th century and is broadly situated in the England is a Country which is part of the United Kingdom. Its inhabitants account for more than 83% of the total UK population whilst its mainland This bone fragment was identified correctly as the lower extremity of the femur of an animal larger than anything living in modern times. The femur is the thigh bone In Humans, it is the longest, most voluminous and strongest Bone. The second dinosaur genus to be identified, Iguanodon, was discovered in 1822 by the English geologist Gideon Mantell, who recognized similarities between his fossils and the bones of modern iguanas. Iguanodon (ɪˈgwɑːnədɒn or /ɪˈgwænədɒn/ meaning " Iguana Tooth " is a Genus of Ornithopod Dinosaur Gideon Algernon Mantell ( February 3, 1790 &ndash November 10 1852) was an English Obstetrician, Geologist Iguana is a Genus of Lizard native to tropical areas of Central and South America and the Caribbean first described by Austrian Two years later, the Rev William Buckland, a professor of geology at Oxford University, unearthed more fossilized bones of Megalosaurus and became the first person to describe dinosaurs in a scientific journal. The Very Rev Dr William Buckland DD ( Axminster, 12 March, 1784 – Islip, 14 August, 1856) was an English Geology (from Greek γη gê, "earth" and λόγος Logos, "speech" lit The University of Oxford (informally "Oxford University" or simply "Oxford" located in the city of Oxford, Oxfordshire, England is the For a broader class of publications which include scientific journals see Academic journal. ^[116]

The study of these "great fossil lizards" soon became of great interest to European and American scientists, and in 1842 the English paleontologist Richard Owen coined the term "dinosaur". Sir Richard Owen KCB ( Lancaster, July 20 1804 &ndash December 18 1892) was an English Biologist He recognized that the remains that had been found so far, Iguanodon, Megalosaurus and Hylaeosaurus, shared a number of distinctive features, and so decided to present them as a distinct taxonomic group. Hylaeosaurus (haɪˌliːoʊˈsɔrəs hye-LEE-oh-SAWR-us) from the Greek words hylē/υλη "forest" and saurus/σαυρος With the backing of Prince Albert of Saxe-Coburg-Gotha, the husband of Queen Victoria, Owen established the Natural History Museum in South Kensington, London, to display the national collection of dinosaur fossils and other biological and geological exhibits. Victoria (Alexandrina Victoria 24 May 1819 – 22 January 1901 was from 20 June 1837 the Queen of the United Kingdom of Great Britain and Ireland The Natural History Museum is one of three large Museums on Exhibition Road, South Kensington, London (the others are the Science Museum South Kensington is a district in the Royal Borough of Kensington and Chelsea in London. London ( ˈlʌndən is the capital and largest urban area in the United Kingdom.

In 1858, the first known American dinosaur was discovered, in marl pits in the small town of Haddonfield, New Jersey (although fossils had been found before, their nature had not been correctly discerned). Marl or Marlstone is a Calcium carbonate or lime -rich mud or Mudstone which contains variable amounts of Clays and Aragonite The creature was named Hadrosaurus foulkii. Hadrosaurus (ˌhædroʊˈsɔrəs from Greek: ἁδρος hadros + σαυρος sauros = sturdy lizard) is a dubious It was an extremely important find; Hadrosaurus was the one of the first nearly complete dinosaur skeletons found and it was clearly a bipedal creature. Bipedalism is a form of Terrestrial locomotion where an organism moves by means of its two rear limbs (The first was in 1834, in Maidstone, Kent, England) This was a revolutionary discovery as, until that point, most scientists had believed dinosaurs walked on four feet, like other lizards. Iguanodon (ɪˈgwɑːnədɒn or /ɪˈgwænədɒn/ meaning " Iguana Tooth " is a Genus of Ornithopod Dinosaur Foulke's discoveries sparked a wave of dinosaur mania in the United States. The United States of America —commonly referred to as the

Dinosaur mania was exemplified by the fierce rivalry between Edward Drinker Cope and Othniel Charles Marsh, both of whom raced to be the first to find new dinosaurs in what came to be known as the Bone Wars. Edward Drinker Cope (July 28 1840&ndashApril 12 1897 was an American paleontologist and comparative anatomist, as well as a noted herpetologist Othniel Charles Marsh ( October 29, 1831 &ndash March 18, 1899) was one of the pre-eminent Paleontologists of the 19th century who The Bone Wars is the name given to a period of intense fossil speculation and discovery during the Gilded Age of American history marked by a heated rivalry between Edward The feud probably originated when Marsh publicly pointed out that Cope's reconstruction of an Elasmosaurus skeleton was flawed; Cope had inadvertently placed the plesiosaur's head at what should have been the animal's tail end. Elasmosaurus (iːˌlæzmoʊˈsɔrəs Greek ελασμος / elasmos = thin plate (referring to thin plates in its Pelvic girdle Plesiosaurs (ˈpliːziəˌsɔɹ ( Greek: plesios/πλησιος meaning 'near' or 'close to' and sauros/σαυρος meaning The fight between the two scientists lasted for over 30 years, ending in 1897 when Cope died after spending his entire fortune on the dinosaur hunt. Marsh 'won' the contest primarily because he was better funded through a relationship with the US Geological Survey. The United States Geological Survey ( USGS) is a scientific agency of the United States government. Unfortunately, many valuable dinosaur specimens were damaged or destroyed due to the pair's rough methods; for example, their diggers often used dynamite to unearth bones (a method modern paleontologists would find appalling). Dynamite is an explosive based on the explosive potential of Nitroglycerin, initially using Diatomaceous earth (kieselgur US Spelling kieselguhr Despite their unrefined methods, the contributions of Cope and Marsh to paleontology were vast; Marsh unearthed 86 new species of dinosaur and Cope discovered 56, for a total of 142 new species. Cope's collection is now at the American Museum of Natural History in New York, while Marsh's is on display at the Peabody Museum of Natural History at Yale University. The American Museum of Natural History ( AMNH) located on the Upper West Side, Manhattan, New York, USA is one of the largest and most New York ( is a state in the Mid-Atlantic and Northeastern regions of the United States and is the nation's third most populous The Peabody Museum of Natural History at Yale University is among the oldest largest and most prolific university natural history museums in the world ^[117]

Since 1897, the search for dinosaur fossils has extended to every continent, including Antarctica. The first Antarctic dinosaur to be discovered, the ankylosaurid Antarctopelta oliveroi, was found on Ross Island in 1986, although it was 1994 before an Antarctic species, the theropod Cryolophosaurus ellioti, was formally named and described in a scientific journal. Ankylosauria is a group of Herbivorous Dinosaurs of the order Ornithischia. Antarctopelta (æntˌʔɑrktəˈpeltə or ant- ARK -to-PEL-ta meaning 'Antarctic shield' was a Genus of Ankylosaurian Dinosaur with Ross Island is an island formed by four Volcanoes in the Ross Sea by Antarctica, off the coast of Victoria Land in McMurdo Sound Cryolophosaurus (ˌkraɪoʊˌlɒfoʊˈsɔrəs or /kraɪˌɒləfəˈsɔrəs/ meaning "cold crest lizard" was a large theropod Dinosaur, with

Current dinosaur "hot spots" include southern South America (especially Argentina) and China. For a topic outline on this subject see List of basic Argentina topics. China ( Wade-Giles ( Mandarin) Chung¹kuo² is a cultural region, an ancient Civilization, and depending on perspective a National China in particular has produced many exceptional feathered dinosaur specimens due to the unique geology of its dinosaur beds, as well as an ancient arid climate particularly conducive to fossilization. The realization that Dinosaurs are closely related to Birds raised the obvious possibility of feathered dinosaurs. FOSSIL is a standard protocol for allowing serial communication for Telecommunications programs under the DOS Operating system.

The "dinosaur renaissance"

Main article: Dinosaur renaissance

The field of dinosaur research has enjoyed a surge in activity that began in the 1970s and is ongoing. The " Dinosaur renaissance " was a small-scale scientific revolution started in the late 1960s which led to renewed academic and popular interest in Dinosaurs This was triggered, in part, by John Ostrom's discovery of Deinonychus, an active predator that may have been warm-blooded, in marked contrast to the then-prevailing image of dinosaurs as sluggish and cold-blooded. John H Ostrom ( February 18, 1928 &ndash July 16, 2005) was an American Paleontologist who revolutionized modern Deinonychus (daɪˈnɒnikəs ( Greek δεινος, 'terrible' and ονυξ/ονυχος, 'claw' was a Genus of carnivorous In Biology, a warm-blooded Animal species is one whose members maintain thermal Homeostasis; that is they keep their body temperature at a roughly constant Cold-blooded organisms (called poikilotherms - "of varying temperature" maintain their body temperatures in ways different from Mammals and Birds Vertebrate paleontology has become a global science. Vertebrate paleontology seeks to discover the behavior reproduction and appearance of extinct spined animals through the study of their Fossilized remains Science (from the Latin scientia, meaning " Knowledge " or "knowing" is the effort to discover, and increase human understanding Major new dinosaur discoveries have been made by paleontologists working in previously unexploited regions, including India, South America, Madagascar, Antarctica, and most significantly in China (the amazingly well-preserved feathered dinosaurs in China have further consolidated the link between dinosaurs and their conjectured living descendants, modern birds). India, officially the Republic of India (भारत गणराज्य inc-Latn Bhārat Gaṇarājya; see also other Indian languages) is a country Madagascar, or Republic of Madagascar (older name Malagasy Republic) is an Island nation in the Indian Ocean off the southeastern China ( Wade-Giles ( Mandarin) Chung¹kuo² is a cultural region, an ancient Civilization, and depending on perspective a National The realization that Dinosaurs are closely related to Birds raised the obvious possibility of feathered dinosaurs. China ( Wade-Giles ( Mandarin) Chung¹kuo² is a cultural region, an ancient Civilization, and depending on perspective a National The widespread application of cladistics, which rigorously analyzes the relationships between biological organisms, has also proved tremendously useful in classifying dinosaurs. Cladistics is the hierarchical classification of Species based on evolutionary ancestry Cladistic analysis, among other modern techniques, helps to compensate for an often incomplete and fragmentary fossil record. FOSSIL is a standard protocol for allowing serial communication for Telecommunications programs under the DOS Operating system.

Cultural depictions

Main article: Cultural depictions of dinosaurs

By human standards, dinosaurs were creatures of fantastic appearance and often enormous size. As such, they have captured the public imagination and become an enduring part of human culture. Only three decades after the first scientific descriptions of dinosaur remains, the famous dinosaur sculptures were erected in Crystal Palace Park in London. The Crystal Palace Dinosaurs, also known as Dinosaur Court, are a series of sculptures of Dinosaurs and extinct Mammals located in Crystal Palace Crystal Palace is a residential area in South London, England named from the erstwhile local landmark The Crystal Palace, which occupied the London ( ˈlʌndən is the capital and largest urban area in the United Kingdom. These sculptures excited the public so strongly that smaller replicas were sold, one of the first examples of tie-in merchandising. A tie-in is an authorized product based on a media property a company is releasing such as a movie or Video / DVD, Computer game, Video game Merchandising refers to the methods practices and operations conducted to promote and sustain certain categories of commercial activity Since Crystal Palace, dinosaur exhibitions have opened at parks and museums around the world, both catering to, and reinforcing, the public interest. A museum is a "permanent institution in the service of society and of its development open to the public which acquires conserves researches communicates and exhibits the ^[118] Dinosaur popularity has long had a reciprocal effect on dinosaur science, as well. The competition between museums for public attention led directly to the Bone Wars waged between Marsh and Cope, each striving to return with more spectacular fossil remains than the other, and the resulting contribution to dinosaur science was enormous. The Bone Wars is the name given to a period of intense fossil speculation and discovery during the Gilded Age of American history marked by a heated rivalry between Edward ^[119]

Dinosaurs hold an integral place in modern culture. The word "dinosaur" itself has entered the English lexicon as an expression describing anything that is impractically large, slow-moving, or obsolete, bound for extinction. In Linguistics, the lexicon (from Greek Λεξικόν of a language is its Vocabulary, including its words and expressions ^[120] The public preoccupation with dinosaurs led to their inevitable entrance into worldwide popular culture. Popular culture (or pop culture) is the Culture — patterns of human activity and the symbolic structures that give such activities significance and importance — Beginning with a passing mention of Megalosaurus in the first paragraph of Charles Dickens' Bleak House in 1852,^[121] dinosaurs have been featured in a broad array of fictional works. Bleak House is the ninth Novel by Charles Dickens, published in twenty monthly installments between March 1852 and September 1853 Fiction is the telling of stories which are not real More specifically fiction is an imaginative form of Narrative, one of the four basic Rhetorical modes. Sir Arthur Conan Doyle's 1912 book The Lost World, the iconic 1933 film King Kong, the 1954 introduction of Godzilla and its many subsequent sequels, the best-selling 1990 novel Jurassic Park by Michael Crichton and its 1993 film version, briefly the highest-grossing film of all time, are just a few prominent examples of the long tradition of dinosaurs in fiction. Sir Arthur Ignatius Conan Doyle, DL (22 May 1859 – 7 July 1930 was an Anglo-Scottish Author most noted for his stories about the The Lost World is a novel released in 1912 by Arthur Conan Doyle concerning an expedition to a Plateau in South America where prehistoric King Kong is a landmark Black-and-white Adventure film about a gigantic Gorilla named " Kong " and how he is captured from is a successful landmark 1954 Japanese Science fiction film directed and co-written by Ishiro Honda with special effects by Eiji Tsuburaya Jurassic Park is a Science fiction Novel that was written by Michael Crichton and published in 1990. John Michael Crichton, ˈkraɪtən, (born October 23 1942 is an American author Film producer, Film director, Medical doctor, and Television producer Jurassic Park is a 1993 Science fiction film directed by Steven Spielberg and based on the novel of the same name by Michael The following is a non-definitive list of the all-time highest-grossing films. Non-fiction authors, including some prominent paleontologists, have also sought to take advantage of dinosaur popularity, especially among children, to educate readers about dinosaurs in particular and science in general. Non-fiction is an account or representation of a subject which is presented as Fact. Dinosaurs are ubiquitous in advertising, with numerous companies seeking to utilize dinosaurs to sell their own products or to characterize their rivals as slow-moving or obsolete. Advertising is a form of Communication that typically attempts to persuade potential Customers to Purchase or to consume more of a particular Brand Generally a company is a form of Business organization. The precise definition varies ^[122]

Religious views

Main article: Young Earth Creationism#Palaeontology and dinosaurs

Various religious groups have views about dinosaurs that differ from those held by the vast majority of scientists, usually due to conflicts with creation stories in their scriptures. Young Earth creationism (YEC is the religious belief that Heaven, Earth, and Life on Earth were created by a direct act of God dating "Creationism" can also refer to Creation myths in general or to a concept about the origin of the soul. However, most of the scientific community rejects these religiously-inspired interpretations of dinosaurs. Scientific method refers to bodies of Techniques for investigating phenomena ^[123][124]

See also

• Dinosaur classification
• Physiology of dinosaurs
• Fossils
• List of dinosaurs
• List of fossil sites (with link directory)
• Prehistoric life
• Prehistoric reptiles

Notes and references

General references

See also

• Dinosaurs Portal
• Dinosauria on Wikimedia Commons

External links

Images

• The Art Gallery of The Dinosauricon, hosting over 2000 images from many different artists working in different styles. Wikimedia Commons (or simply Commons) is a repository of Free content images sound and other multimedia files
• Skeletal Drawing Professional restorations of numerous dinosaurs, and discussions of dinosaur anatomy.

Popular

• Dinosaurs & other extinct creatures: From the Natural History Museum, a well illustrated dinosaur directory. The Natural History Museum is one of three large Museums on Exhibition Road, South Kensington, London (the others are the Science Museum
• Dinosaurnews (www. dinosaurnews. org) The dinosaur-related headlines from around the world. Recent news on dinosaurs, including finds and discoveries, and many links.
• Dinosauria From UC Berkeley Museum of Paleontology Detailed information - scroll down for menu.
• LiveScience.com All about dinosaurs, with current featured articles.
• Dino Russ's Lair hosts a large collection of dinosaur-related links.
• Zoom Dinosaurs (www. enchantedlearning. com) From Enchanted Learning. Kids' site, info pages and stats, theories, history.

Technical

• Palaeontologia Electronica From Coquina Press. Online technical journal.
• Dinobase A searchable dinosaur database, from the University of Bristol, with dinosaur lists, classification, pictures, and more.
• DinoData (www. dinodata. org) Technical site, essays, classification, anatomy.
• Dinosauria On-Line (www. dinosauria. com) Technical site, essays, pronunciation, dictionary.
• The Dinosauricon By T. Michael Keesey. Technical site, cladogram, illustrations and animations.
• Thescelosaurus! By Justin Tweet. Includes a cladogram and small essays on each relevant genera and species.
• Dinosauromorpha Cladogram From Palaeos. A detailed amateur site about all things paleo.
• The Dinosaur Encyclopaedia, an extensive overview of genera-based dinosaur information from 1999 and before.

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