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Orthocerida
Fossil range: Ordovician - Permian, possibly to Triassic or Cretaceous
Scientific classification
Kingdom: Animalia
Phylum: Mollusca
Class: Cephalopoda
Subclass: Nautiloidea
Order: Orthocerida
Kuhn, 1940
Families

Orthoceratidae
(or Michelinoceratidae)
Geisonoceratidae
Proteoceratidae
Stereoplasmoceratidae
Clinoceratidae
Paraphragmitidae
Pseudorthoceratidae
Arionoceratidae
Lamellorthoceratidae
and others

Orthocerida are an order of extinct nautiloid cephalopods that lived from the Early Ordovician (about 500 million years ago) to the Late Permian (250 Ma) or Late Triassic (200 Ma). The Ordovician is a geologic period and system, the second of six of the Paleozoic era, and covers the time between 488 The Permian is a geologic period and system that extends from 299 The Triassic is a geologic period and system that extends from about 251 to 199 Ma (million years ago The Cretaceous (kriːˈteɪʃəs, usually abbreviated 'K' for its German translation "Kreide" is a geologic period and system, reaching from the end of Molluscs are animals belonging to the phylum Mollusca. There are around 250000 extant Species within the phylum with an estimated 70000 The cephalopods ( Greek plural (kephalópoda "head-feet" are the Mollusc class Cephalopoda characterized by Nautiloids are a group of marine Mollusks in the subclass Nautiloidea, which all possess an external shell the best-known example being the modern Nautiluses Oskar Kuhn is a German Palaeontologist. ---- Among his books are Paläozoologie in Tabellen (1940 Year 1940 ( MCMXL) was a Leap year starting on Monday (link will display the full 1940 calendar of the Gregorian calendar. In Biological classification, family ( Latin Orthoceratidae are a family of extinct Nautiloid Cephalopods It is also known as Michelinoceratidae. Orthoceratidae are a family of extinct Nautiloid Cephalopods It is also known as Michelinoceratidae. Nautiloids are a group of marine Mollusks in the subclass Nautiloidea, which all possess an external shell the best-known example being the modern Nautiluses The cephalopods ( Greek plural (kephalópoda "head-feet" are the Mollusc class Cephalopoda characterized by The Ordovician is a geologic period and system, the second of six of the Paleozoic era, and covers the time between 488 The Permian is a geologic period and system that extends from 299 The Triassic is a geologic period and system that extends from about 251 to 199 Ma (million years ago This order is also called Michelinocerida. One fossil find suggests they survived until the Early Cretaceous (100 Ma). The Cretaceous (kriːˈteɪʃəs, usually abbreviated 'K' for its German translation "Kreide" is a geologic period and system, reaching from the end of But the orthocerids were most common and diverse from the Ordovician to the Devonian. The Devonian is a geologic period and system of the Paleozoic era spanning from to  million years ago.

Contents

Shell form

The shell is usually long, and may be straight ("orthoconic") or gently curved. An orthocone is a usually long straight shell of a Nautiloid Cephalopod. In life, these animals may have been similar to the modern squid, except for the long shell. Squid are marine Cephalopods of the order Teuthida, which comprises around 300 species The internal structure of the shell consists of concavo-convex chambers linked by a centrally-placed tube called a siphuncle. In Biology, Camera can refer to Camera (anatomy, spaces or chambers enclosed between two adjacent septa in the Phragmocone The siphuncle is a strand of tissue passing longitudinally through the shell of a Cephalopod Mollusk. There is a tendency for the chambers to develop cameral deposits, which were used as ballast to balance the long gas-filled shell. In Biology, Camera can refer to Camera (anatomy, spaces or chambers enclosed between two adjacent septa in the Phragmocone Depending on the family, the siphuncle has orthochoanitic or cyrtochoanitic septal necks. In Biological classification, family ( Latin The shell surface may be (depending on the species or genus) smooth, transversely ribbed, or ornamented by a network of fine lirae. Lirae (sing lira are fine lines or ridges (much finer than ribs that serve as ornament on Mollusc (e Fossils are common and have been found on many continents, including the Americas, Africa, Europe, and Asia. FOSSIL is a standard protocol for allowing serial communication for Telecommunications programs under the DOS Operating system. The Americas are the lands of the Western hemisphere or New World, consisting of the Continents of North America and South America

Ecology

Orthocerids may have swum near the sea bed with their buoyant shell resting horizontally in the water, although some workers have suggested they floated more passively among the plankton or rested on the sea floor. In Physics, buoyancy ( BrE IPA: /ˈbɔɪənsi/ is the upward Force on an object produced by the surrounding liquid or gas in which it is Like modern cephalopods they would have used jet-propulsion for locomotion. However, the long bulky shell and relatively weak muscle attachments make it unlikely that they were as agile as ammonoids or modern cephalopods. Ammonites are an extinct group of marine animals of the subclass Ammonoidea in the class Cephalopoda phylum They most likely fed on trilobites and small arthropods. Trilobites ("three-lobes" are extinct Arthropods that form the class Trilobita. Arthropods are Animals belonging to the Phylum Arthropoda (from Greek ἄρθρον arthron, " Joint "

Taxonomy

Orthocerid taxonomy is rife with problems, because the mature shell has few useful characteristics, and even those that it does have are subject to repeated homeomorphy and iterative evolution. Taxonomy is the practice and science of classification The word comes from the Greek, taxis (meaning 'order' 'arrangement' and, nomos A recent study of very well-preserved embryonic shells of the family Pseudorthoceratidae from the Imo Formation (Early Carboniferous) reveals that the morphologic diversity of the early growth stages of these creatures is far more diverse than would be expected. A protoconch (meaning first or earliest or original shell is an Embryonic or Larval shell of some classes of Molluscs e Although this indicates that the family Pseudorthoceratidae is in need of revision, it also shows the value of embryonic shell morphology in understanding orthocerid evolutionary relationships. The term morphology in Biology refers to the outward appearance ( Shape, Structure, Colour, Pattern) of an Organism It is also likely that the stratigraphic ranges of current taxa are overestimated (because different lineages may appear superficially to belong to the same taxon). A taxon (plural taxa) or taxonomic unit, is a name designating an organism or a group of Organisms In Biological nomenclature according to (Kröger and Mapes 2004)

Evolutionary history

The orthocerids probably arose from the Baltoceratidae, a family of the Ellesmerocerida. The Ellesmerocerida comprise early Nautiloid cephalopods from the late Upper Cambrian (Trempealeauan and Ordovician that are typically rather small with close

However, several workers have disputed the monophyly of the Orthocerida as traditionally defined, and some have criticized it as a "nightmare for taxonomists" lacking clearly defined characters. A clade is a taxonomic group comprising a single Common ancestor and all the descendants of that ancestor Orthocerida as usually understood may thus be a polyphyletic group, having arisen as several lineages from early Ordovician cephalopods. In Phylogenetics, a Taxon is polyphyletic ( Greek for "of many races" if the trait its members have in common evolved separately in different The Ordovician is a geologic period and system, the second of six of the Paleozoic era, and covers the time between 488 Some workers have split off the Pseudorthocerida and Dissidocerida as separate orders, the latter on the grounds that it arose from a different baltoceratid ancestor. The pseudorthocerids are thought to be distinct because their protoconch and septal necks are so different. A protoconch (meaning first or earliest or original shell is an Embryonic or Larval shell of some classes of Molluscs e

Orthocerids flourished in the Paleozoic Era, giving rise to such intriuging forms as the ascocerids and Lituites. The Paleozoic or Palaeozoic Era (from the Greek palaio (παλαιο "old" and zoe (ζωη "life" meaning "ancient life" Ascocerida is an order of extinct Nautiloid Cephalopods The shell slightly exogastrical is morphologically very reduced Lituites is an extinct Genus of the Nautiloids and is one of the most primitive known Cephalopods It originated in the Ordovician Moreover, the spherical protoconch, or first chamber, of some orthocerids suggests they were ancestors to the Bactritida, small orthocones that spawned both the ammonoids and coleoids. A protoconch (meaning first or earliest or original shell is an Embryonic or Larval shell of some classes of Molluscs e In Biology, Camera can refer to Camera (anatomy, spaces or chambers enclosed between two adjacent septa in the Phragmocone The Bactritida form a small order of more or less straight-shelled (orthoconic Cephalopods that first appeared during the Emsian Stage of the Devonian Ammonites are an extinct group of marine animals of the subclass Ammonoidea in the class Cephalopoda phylum Subclass Coleoidea is the grouping of Cephalopods containing all the primarily soft-bodied creatures Fossilized radulas from orthocerids also suggest a closer affinity with modern coleoids than with Nautilus. The radula is a toothed Chitinous ribbon typically used for scraping cutting and chewing food before it enters the Esophagus. This implies that some orthocerids, such as the Lamellorthoceratidae, Arionoceratidae, Michelinoceratidae, and Sphaerorthoceras, belong in the same "Neocephalopoda" clade as coleoids and ammonoids. Neocephalopods are a group of Cephalopod Mollusks that include the Coleoids and all extinct species that are more closely related to extant

There is some dispute when the orthocerids finally became extinct. Although they are often said to have survived into the Triassic Period, the two genera that date from that period may actually be pseudorthocerids. In that case, the last orthocerids may date only to the Permian. However, the discovery in the Caucasus of a possible orthocerid from the Early Cretaceous Period suggests that they may have endured much longer as a ghost lineage. The Early Cretaceous ( timestratigraphic name or the Lower Cretaceous ( logstratigraphic name is the earlier of the two major divisions of the Cretaceous

References

External links

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