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Hesperornithes
Fossil range: Late Cretaceous (Albian - Maastrichtian)
Hesperornis
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Aves
Subclass: Hesperornithes
Fürbringer, 1888
Order: Hesperornithiformes
Sharpe 1899
Families

Enaliornithidae
Baptornithidae
Hesperornithidae
Synonyms

Odontornithes Marsh, 1873 (partim)
Odontolcae Marsh, 1875
Gaviomorphae Cracraft, 1982 (partim)

Hesperornithes is an extinct and highly specialized clade of Cretaceous toothed birds. Late Cretaceous (100mya - 65mya refers to the second half of the Cretaceous Period, named after the famous white Chalk cliffs of southern England Albian ( French Albion, from Alba = Aube in France) is a stage of the Cretaceous period. The Maastrichtian is the last stage of the Cretaceous period, and therefore of the Mesozoic era. Hesperornis is an extinct Genus of flightless aquatic Birds that lived during the Santonian to Campanian sub-epochs of the Chordates ( Phylum Chordata) are a group of Animals that includes the Vertebrates together with several closely related Invertebrates Birds ( class Aves) are bipedal endothermic ( Warm-blooded) Vertebrate animals that lay eggs. Max Fürbringer ( January 30, 1846 – March 6, 1920) was a German anatomist. Year 1888 ( MDCCCLXXXVIII) was a Leap year starting on Sunday (click on link for calendar of the Gregorian calendar (or a Richard Bowdler Sharpe ( 22 November 1847 - 25 December 1909) was an English Zoologist. Year 1899 ( MDCCCXCIX) was a Common year starting on Sunday (link will display the full calendar of the Gregorian calendar (or a Common In Biological classification, family ( Latin Enaliornis is a Genus of Hesperornithine Bird which lived in the late Early Cretaceous, making it the oldest known hesperornithine Baptornis ("diving bird" is an extinct Genus of flightless aquatic Bird from the Late Cretaceous, some 87-80 million In Scientific nomenclature, synonyms are different Scientific names used for a single Taxon. Odontornithes is an obsolete taxonomic term proposed by O C Marsh for Birds possessing Teeth, notably the genera Hesperornis Othniel Charles Marsh ( October 29, 1831 &ndash March 18, 1899) was one of the pre-eminent Paleontologists of the 19th century who Year 1873 ( MDCCCLXXIII) was a Common year starting on Wednesday (link will display the full calendar of the Gregorian calendar (or a Common Othniel Charles Marsh ( October 29, 1831 &ndash March 18, 1899) was one of the pre-eminent Paleontologists of the 19th century who Year 1875 ( MDCCCLXXV) was a Common year starting on Friday (link will display the full calendar of the Gregorian calendar (or a Common Year 1982 ( MCMLXXXII) was a Common year starting on Friday (link displays the 1982 Gregorian calendar) A clade is a taxonomic group comprising a single Common ancestor and all the descendants of that ancestor The Cretaceous (kriːˈteɪʃəs, usually abbreviated 'K' for its German translation "Kreide" is a geologic period and system, reaching from the end of Birds ( class Aves) are bipedal endothermic ( Warm-blooded) Vertebrate animals that lay eggs. Hesperornithine birds, apparently limited to former aquatic habitats in the Northern Hemisphere, include genera such as Hesperornis, Parahesperornis, Baptornis, Enaliornis, and probably Potamornis, all strong-swimming predatory waterbirds. A genus (plural genera from Γένος Latin genus "descent family type gender" is a low-level Taxonomic Many, if not all species were completely flightless. The largest known hesperornithine, described in 1999 and named Canadaga arctica, may have reached a maximum adult length of over 1. Year 1999 ( MCMXCIX) was a Common year starting on Friday (link will display full 1999 Gregorian calendar) Canadaga is a prehistoric Flightless bird Genus from the Late Cretaceous. 5 meters (five feet).

Hesperornithine birds were, strictly speaking, the only Mesozoic dinosaurs to colonize the oceans (technically speaking, all birds are dinosaurs); the aquatic reptiles of their time, such as the ichthyosaurs and plesiosaurs, were not dinosaurs. The Mesozoic Era is one of three geologic eras of the Phanerozoic eon. Birds ( class Aves) are bipedal endothermic ( Warm-blooded) Vertebrate animals that lay eggs. 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 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 Hesperornithine birds went extinct at the K-T boundary, along with enantiornithine protobirds, all non-avian dinosaurs, and many other life forms. The Cretaceous–Tertiary extinction event, which occurred approximately ( Ma) was a large-scale mass extinction of animal and plant species in a geologically Enantiornithes is an extinct group of primitive Birds They were the most abundant and diverse avialans of the Mesozoic.

Contents

Anatomy and ecology

Most of what is known about this group rests on analyses of single species, as few provide sufficiently diverse fossils for analysis. FOSSIL is a standard protocol for allowing serial communication for Telecommunications programs under the DOS Operating system. In most cases, what holds true for one hesperornithine also applies to the others, as these birds were quite stereotypical and extreme in their autapomorphies. An autapomorphy in Cladistics is a derived trait that is unique to a given terminal group

Although some of the smaller species might have been able to fly, Hesperornis and Baptornis had only vestigial wings. Like living foot-propelled diving birds, the femur and metatarsus were short, whereas the tibia was long. The legs were also set far back on the body, as in loons, grebes or penguins. The loons (eg North America or divers (eg UK/Ireland are a group of aquatic birds found in many parts of North America and northern Eurasia Grebes are members of the Podicipediformes order, a widely distributed order of freshwater diving birds some of which visit the sea when migrating Penguins ( order Sphenisciformes, family Spheniscidae) are a group of aquatic, flightless Birds living almost Hesperornithids must have been powerful swimmers and divers but extremely ungainly on the land, and probably spent little time ashore except to nest (indeed, it has been suggested that they did not incubate their eggs).

Some researchers think that on land they had to slide on their bellies and push with their legs; the hip and knee joints were shaped such that these birds could not move them dorsoventrally, and in a resting position the feet projected sideways from the body, which would have prevented them from walking upright. Whereas Hesperornis had probably lobes of skin on its toes similar to the grebes of today, the toes of Baptornis could not rotate (necessary in lobed feet to reduce drag) and thus were more likely webbed, as in loons. Grebes are members of the Podicipediformes order, a widely distributed order of freshwater diving birds some of which visit the sea when migrating The loons (eg North America or divers (eg UK/Ireland are a group of aquatic birds found in many parts of North America and northern Eurasia The dense bones of these birds decreased their buoyancy, making diving easier[1].

The beak was long, probably hooked at the tip, and bore a series of simple, sharp teeth which were set into a longitudinal groove. These and probably helped to seize fish, as does the serrated beak of mergansers today; unlike the reptilian teeth of other toothed birds, those of the hesperornithids were unique[2]. Fish are aquatic Vertebrate animals that are typically ectothermic (previously Cold-blooded) covered with scales, and equipped with two Mergus is the Genus of the typical mergansers, fish-eating Ducks in the Seaduck subfamily (Merginae Given that teeth are induced by a rather simple genetic mechanism[3], it is even possible that these birds re-evolved them and that some ancestors of the hesperornithids were toothless.

Systematics and evolution

These birds were originally combined with Ichthyornis in the paraphyletic "Odontornithes" by Othniel Charles Marsh, in 1873. Ichthyornis is a Genus of Seabird from the Late Cretaceous of North America. 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 Odontornithes is an obsolete taxonomic term proposed by O C Marsh for Birds possessing Teeth, notably the genera Hesperornis Othniel Charles Marsh ( October 29, 1831 &ndash March 18, 1899) was one of the pre-eminent Paleontologists of the 19th century who In 1875, they were separated as Odontolcae. The group was often considered to be allied to loons and grebes[4], or to the Paleognathae[5]. The Paleognathae or paleognaths ("old jaws" are one of the two living Superorders of Birds The other living superorder is Neognathae These similarities, however, as the more recently determined fact that the osteons of their bones - at least in Hesperornis - were arranged in a pattern similar to that in Neognathae[6], are today considered to be due to convergent evolution[7]. The osteon, or Haversian system is the fundamental functional unit of compact bone. Neognaths ( Neognathae) are Birds within the Subclass Neornithes of the class Aves. Convergent evolution describes the acquisition of the same biological trait in unrelated lineages

Currently, the hesperornithine birds are recognized as a very specialized lineage that is not ancestral or otherwise closely related to the birds of today. Still, their relationship is close enough that they probably diverged from the ancestors of today's birds as late as the earliest Cretaceous. The Cretaceous (kriːˈteɪʃəs, usually abbreviated 'K' for its German translation "Kreide" is a geologic period and system, reaching from the end of

The discovery that Gansus yumenensis, which lived some time before the main radiation of hesperornithids, was a primitive member of the Ornithurae - that is, birds which had developed the type of pygostyle that is also found in modern birds - suggests that the ancestors of Hesperornithes - which also ornithuran - may have been birds generally similar to Gansus and living some 130-150 mya. Gansus is a Genus of aquatic Birds that lived during the Albian stage of the Early Cretaceous period (around 110 million Ornithurae (meaning "bird tails" in Greek) is the name of a natural group of Birds coined by Ernst Haeckel in 1866 Pope's nose redirects here It may also refer to the license plate light on early Volkswagen Beetles Pygostyle refers to a number of the In Astronomy, Geology, and Paleontology, mya or " mya " is an abbreviation for "million years ago". Given the tendency of birds that have become flightless to increase in size markedly in just a few million years, the probability of Hesperornithes deriving from an animal at least superficially similar and not too far related to Gansus is quite high. The new fossil material of that species should assist in determining the number of synapomorphies of hesperornithines and other ornithurans, which have until now been muddied by the numerous autapomorphies of the former. In Evolutionary biology, a synapomorphy is a derived Character state shared by two or more terminal groups ( taxa included in a Cladistic analysis An autapomorphy in Cladistics is a derived trait that is unique to a given terminal group

Loss and/or fusion of caudal vertebrae in pygostyle-like structures was a general trend in Cretaceous avian evolution, and a full pygostyle and associated structures may have evolved more than once to similar shapes. The coccyx (pronounced kok -siks (Latin os coccygis) commonly referred to as the tailbone, is the final segment of the human vertebral column Pope's nose redirects here It may also refer to the license plate light on early Volkswagen Beetles Pygostyle refers to a number of the The fact that Gansus had non-pneumatized, dense bones, like those of hesperornithines, although it was not a specialized diver, is interesting to note. Similarly, the bone structure of Hesperornis indicates that as opposed to Enantiornithes and in line with other Ornithurae it showed rapid, uninterrupted growth to adult size [1]. Enantiornithes is an extinct group of primitive Birds They were the most abundant and diverse avialans of the Mesozoic.

The earliest known hesperornithine is the Early Cretaceous Enaliornis although these birds are somewhat tentatively assigned to this group because of the bad preservation of their remains; the majority of hesperornithine taxa are known from the Late Cretaceous. The Early Cretaceous ( timestratigraphic name or the Lower Cretaceous ( logstratigraphic name is the earlier of the two major divisions of the Cretaceous Enaliornis is a Genus of Hesperornithine Bird which lived in the late Early Cretaceous, making it the oldest known hesperornithine A taxon (plural taxa) or taxonomic unit, is a name designating an organism or a group of Organisms In Biological nomenclature according to Late Cretaceous (100mya - 65mya refers to the second half of the Cretaceous Period, named after the famous white Chalk cliffs of southern England Small hesperornithine bones are known from the freshwater deposits of the Late Cretaceous of the Judith River Group as well as the Hell Creek and Lance Formations as well as Eurasian sites. The Judith River Group is a group of geologic formations in western North America dating from the late Cretaceous and noted as a site for the extensive 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 The Lance (Creek Formation is a division of Late Cretaceous rocks in the western United States For the superstate in George Orwell 's novel see Nations of Nineteen Eighty-Four. These birds were about the size of a cormorant or a loon. Less well-verified is the presence of the lineage around Antarctica, which was a temperate, ice-free region in their time.

Systematics

Hesperornis regalis reconstruction by Marsh. Though a popular depiction, the bird is now known to have been completely unable to assume such a posture. See above for correct position of the legs
Hesperornis regalis reconstruction by Marsh. Othniel Charles Marsh ( October 29, 1831 &ndash March 18, 1899) was one of the pre-eminent Paleontologists of the 19th century who Though a popular depiction, the bird is now known to have been completely unable to assume such a posture. See above for correct position of the legs

Subclass HESPERORNITHES[8]
This is usually treated as equivalent with Hesperornithiformes. Hesperornithes is an extinct and highly specialized Clade of Cretaceous toothed Birds Hesperornithine birds apparently limited to former aquatic habitats However, given the uncertainties of the evolution of teeth and flightlessness in the Hesperornithes, as noted above, it is here considered a distinct group, so that ancestral taxa do not have to be placed together with more advanced ones.

Sometimes assigned to the Hesperornithes, but actual relationships unclear

Footnotes

  1. ^ a b Chinsamy et al. Hargeria redirects here This is also an (invalid name of a genus of Tanaidacean Crustaceans in the family Leptocheliidae. Neogaeornis is a controversial prehistoric Genus of diving Bird. Potamornis is a prehistoric Bird Genus that dated back to the late Maastrichtian. (1998)
  2. ^ Discussed in Marsh (1880), Gregory, (1952).
  3. ^ Discussed at length by Harris et al. (2006).
  4. ^ E. g. by Cracraft (1982). That study is interesting example of how to arrive at an essentially phenetic - and utterly incorrect - analysis in spite of using cladistic methods. Phenetics should not be confused with Phonetics, the study of speech sounds despite the similarity in pronunciation Cladistics is the hierarchical classification of Species based on evolutionary ancestry
  5. ^ Based on a perceived similarity of the bony palate (Gingerich 1973). The hard palate is a thin horizontal bony plate of the Skull, located in the roof of the mouth
  6. ^ See Houde (1987).
  7. ^ This is not a new theory; it was proposed by Stolpe as early as 1935. See also Bogdanovich (2003).
  8. ^ Based on Marsh (1880), Feduccia (1996), Tokaryk, Cumbaa & Storer (1997), and Galton & Martin (2002) (via Haaramo, 2005), as well as Clarke (2004) and Sereno (2005)
  9. ^ Mentioned but not discussed by Dyke et al. (2006): "This material probably pertains to a smaller [hesperornithine] taxon, an area for future work. A taxon (plural taxa) or taxonomic unit, is a name designating an organism or a group of Organisms In Biological nomenclature according to "
  10. ^ A loon-sized hesperornithine (Longrich 2006).

References

External links

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