Ichthyornis

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Ichthyornis
Fossil range: Late Cretaceous

Ichthyornis dispar was probably more streamlined in life than in this reconstruction (Clarke 2004:2)

Scientific classification

Kingdom:	Animalia
Phylum:	Chordata
Class:	Aves
Subclass:	Ichthyornithes Marsh, 1873
Order:	Ichthyornithiformes Fürbringer, 1888
Family:	Ichthyornithidae Marsh, 1873
Genus:	Ichthyornis Marsh, 1872
Species:	I. dispar

Binomial name

Ichthyornis dispar
Marsh, 1872

Synonyms

see article text

Ichthyornis is a genus of seabird from the Late Cretaceous of North America. Its fossil remains are known from the Cretaceous (Turonian-Middle Campanian, 93.5-75 mya) chalks of Alberta, Alabama, Kansas, New Mexico, Saskatchewan, and Texas, which were laid down in the Western Interior Seaway; some fossils from other locations like Argentina and Central Asia are sometimes referred to this taxon.

It is thought that Ichthyornis was the Cretaceous ecological equivalent of modern seabirds such as gulls, petrels, and skimmers.

Although the wings and breastbone are very modern in appearance (suggesting strong flight ability), the jaws retained numerous small, sharp teeth. Unlike earlier birds such as Enantiornithes, it appears to have grown up in a rather short, continuous process (Chinsamy et al. 1998).

Ichthyornis was first discovered in 1870. Othniel Charles Marsh's 1880 monograph on "Odontornithes" remains the most important general reference on this animal. Of the several described species, only one, Ichthyornis dispar, is currently recognized following the seminal review by Clarke (2004). However, many bird species show little difference in their skeletons, and the Ichthyornis material comes from a wide range of strata, so possibly more than one species existed, the bauplan being so successful as to change little in morphology.

The fossil material is known to contain bones of immature individuals (Chinsamy et al. 1998). It has not been thoroughly analyzed according to ontogenetical size differences, as for this, destruction of the fossils would be necessary.

[edit] Systematics

Replica of Ichthyornis skeleton at Yale University, Peabody Museum. See Clarke (2004) for details.

Ichthyornis is close to the ancestry of modern birds, the Neornithes, but represents an independent lineage. It was long believed that it was closely related to some other Cretaceous taxa known from very fragmentary remains—Ambiortus, Apatornis (including the now separated Iaceornis) and Guildavis—but these seem to be closer still to the ancestors of modern birds. New data on the radiation of the latter, which is now known to have started already in the Cretaceous (see Vegavis), could shed more light on the exact relationship of these taxa. Following Clarke (2004), the former order Ichthyornithiformes and the family Ichthyornithidae are now superseded by the subclass Ichthyornithes, which in the paper was also defined according to phylogenetic taxonomy.

There has been considerable confusion about the attribution of the fossil material (Clarke, 2004). The similarity of the lower jaw and teeth to those of mosasaurs (fish-eating marine lizards) is so great that as late as 1952, it was argued that it really belonged to a diminutive species or young individual of or related to the genus Clidastes (Gregory, 1952); it was described as Colonosaurus mudgei.

Of the several species described, only one is usually recognized following Clarke (2004). It is, however, entirely possible that several species have once existed, given the large spatial and temporal range over which fossils have been found.

Synonyms:

Subclass-level
- Odontotormae Marsh, 1875
Genus-level
- Plegadornis Wetmore, 1962 (non C. L. Brehm, 1855)
- Angelinornis Kashin 1972 - nomen novum for Plegadornis Wetmore, 1962 (preoccupied)
Species-level
- Colonosaurus mudgei Marsh, 1872
- Ichthyornis anceps (Marsh, 1872: Graculavus anceps)
- Ichthyornis agilis (Marsh, 1873: Graculavus agilis)
- Ichthyornis victor Marsh, 1876
- Ichthyornis lentus (Marsh, 1877: Graculavus lentus)
- Ichthyornis tener Marsh, 1880
- Ichthyornis validus Marsh, 1880
- Ichthyornis antecessor (Wetmore, 1962: Plegadornis antecessor. Also Angelinornis antecessor)

[edit] See also

Extinct animals in popular culture

[edit] References

Chinsamy, A.; Martin, Larry D. & Dobson, P. (1998): Bone microstructure of the diving Hesperornis and the volant Ichthyornis from the Niobrara Chalk of western Kansas. Cretaceous Research 19(2): 225-235. DOI:10.1006/cres.1997.0102 (HTML abstract)

Clarke, Julia A. (2004): Morphology, Phylogenetic Taxonomy, and Systematics of Ichthyornis and Apatornis (Avialae: Ornithurae). Bulletin of the American Museum of Natural History 286: 1-179 PDF fulltext