Caenagnathidae
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Caenagnathidae ("recent jaws") is a family of bird-like theropod dinosaurs within the clade Oviraptorosauria. While more advanced than earlier oviraptorosaurs like Caudipteryx, caenagnathids were fairly primitive compared to their close relatives the oviraptorids. Whereas oviraptorids had highly shortened snouts, caenagnathid jaws were long and unspecialized (though they still possessed the distinctive beaks of other oviraptorosaurs). Additionally, caenagnathids had typical theropod arms, with a relatively short third finger--all traits that were modified in the oviraptorids, which had longer arms and fingers, as well as comparatively short legs.
The family Caenagnathidae, together with its sister group the Oviraptoridae, comprises the superfamily Caenagnathoidea. In phylogenetic taxonomy, the clade Caenagnathidae is defined as the most inclusive group containing Chirostenotes but not Oviraptor. Though only six species of caenagnathids are currently recognized by paleontologists, the family has a notably confused taxonomic history. Much of this centers on the first caenagnathid to be described, Chirostenotes. Due to the poor preservation of most caenagnathid remains and resulting misidentifications, different bones and different specimens of Chirostenotes have historically been assigned to a number of different species. One of these was the family's namesake, Caenagnathus. While Caenagnathus is today considered a junior synonym of Chirostenotes, it was the first for which a family was named, so while the genus name Caenagnathus is no longer in use, the family name Caenagnathidae remains valid.
The name Caenagnathus (and hence Caenagnathidae) means "recent jaws"--when first discovered, it was thought that caenagnathids were close relatives of paleognath birds (such as the ostrich) based on features of the lower jaw. Since it would be unusual to find a recent group of birds in the Cretaceous, the name "recent jaws" was applied. Most paleontologists, however, now think that the birdlike features of the jaw were acquired convergently with modern birds.
[edit] Species
Today, Caenagnathidae usually contains six species in three genera. However, a few paleontologists consider Elmisaurus elegans to be a junior synonym of Chirostenotes, as they both occur in the same North American locality, far from the Asian species Elmisaurus rarus (Sues, 1997). The genus Caenagnathasia was originally placed in this family, but it is probably more primitive, lying outside both Caenagnathidae and Oviraptoridae within the superfamily Caenagnathoidea (Currie, Godfrey, and Nessov, 1994). Additionally, Maryańska, Osmólska, and Wołsan (2002) consider the oviraptorosaur with a pygostyle, Nomingia, a member of this family.
Caenagnathidae includes -
- Chirostenotes pergracilis, the first known caenagnathid, described initially from two hands and a partial lower arm. Many subsequently named species have been referred to this species, adding to the known fossil material.
- Chirostenotes sternbergi, a more gracile caenagnathid. Some consider Elmisaurus elegans to be the same animal, as both are smaller and more slender than C. pergracilis. It is also possible that this species represents a different gender of the larger C. pergracilis specimens.
- Chirostenotes sp., a possible new species, has been identified from part of a lower jaw found in Montana, but not named (Currie, Godfrey, and Nessov, 1994).
- Elmisaurus rarus, the only known Asian caenagnathid (excluding Caenagnathasia), is known only from elements of the foot.
- Elmisaurus elegans, a smaller Canadian species originally described as a species of Ornithomimus. It may be the same species as Chirostenotes.
- Hagryphus giganteus, the largest described member of the Caenagnathidae at 3 meters long, is also one of the largest oviraptorosaurs known, though it is known only from a complete hand and portion of the arm.
- The "Triebold caenagnathid", an infamous possible new species or genus collected by Triebold Paleontology of South Dakota. Known from two excellently preserved specimens, this species, having been obtained by private collectors, was put up for sale, making its scientific future unknown until it was acquired by the Carnegie Museums of Pittsburgh. An apparently giant species with a well preserved skull and evidence of an oviraptorid-like crest, it is currently awaiting a published description.
[edit] References
- Barsbold, R., Maryańska, T., and Osmólska, H. (1990). "Oviraptorosauria." pg. 249-258 in Weishampel, Dodson, and Osmolska (eds.) The Dinosauria, University of California Press (Berkeley).
- Cracraft, J. (1971). "Caenagnathiformes: Cretaceous birds convergent in jaw mechanism to dicynodont reptiles." Journal of Paleontology, 45: 805-809.
- Currie, P.J., Godfrey, S.J., and Nessov, L.A. (1994). "New caenagnathid (Dinosauria: Theropoda) specimens from the Upper Cretaceous of North America and Asia." Canadian Journal of Earth Sciences -- Revue de Canadienne des Sciences de la Terre, 30: 2255-2272.
- Maryańska, T., Osmólska, H., and Wołsan, M. (2002). "Avialan status for Oviraptorosauria." Acta Palaeontologica Polonica, 47 (1): 97-116.
- Sternberg, R.M. (1940). "A toothless bird from the Cretaceous of Alberta." Journal of Paleontology, 14 (1): 81-85.
- Sues, H.-D. (1997). "On Chirostenotes, a Late Cretaceous oviraptorosaur (Dinosauria: Theropoda) from western North America." Journal of Vertebrate Paleontology, 17 (4): 698-716.
