Caenagnathidae
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| Caenagnathids Fossil range: Late Cretaceous |
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Caenagnathidae ("recent jaws," as derived from Greek kainos and gnathos) is a family of bird-like maniraptoran theropod dinosaurs within the clade Oviraptorosauria, first coined as an order of advanced flightless birds by Charles Hazelius Sternberg in 1940.[1] While more advanced than earlier oviraptorosaurs like Caudipteryx, caenagnathids were fairly primitive compared with their close relatives the oviraptorids, though this by no means reduces the distinct variation and unique nature of the group. Whereas oviraptorids had highly shortened snouts, caenagnathid jaws were long and shallow with an elongated dentary and extended symphysis. Indeed, the jaw of a caenagnathid is its most distinctive feature, historically, whose surface and internal structure is distinct from that of other dinosaurs, including oviraptorids.[2] Caenagnathids are best known for their cranial anatomy, but the earliest forms are known from their postcrania alone, and include such novel features as a fused ankle (as also seen in similar and possibly related Avimimus portentosus), an extremely short tail, possibly with a pygostyle as in Nomingia gobiensis[3], and with exceptionally slender and long legs, giving them a gracile, long-legged appearance that may have resembled some of the smaller ratite birds, such as the emu.
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[edit] Etymology
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.[4][5]
[edit] Classification
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 pergracilis but not Oviraptor philoceratops. While in the past twenty years, only about two to six species were commonly recognized as belonging to the Caenagnathidae, currently that number may be much greater, with new discoveries and theories about older species that may inflate this number to up to ten. Much of this historical difference centers on the first caenagnathid to be described, Chirostenotes pergracilis. 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. For example, the feet of one species, Macrophalangia canadensis[6], were known from the same region from which Chirostenotes pergracilis was recovered, but the discovery of a new specimen with both hands and feet preserved[7] provided the support to combine them, while the later discovery of a partial skull with hands and feet[8] suggested that Chirostenotes and Caenagnathus were the same animal. While Caenagnathus collinsi is today considered to be a likely junior synonym of Chirostenotes pergracilis, 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 due to its inclusion of Caenagnathus.
[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 sternbergi, as they both occur in the same North American locality, far from the Asian species Elmisaurus rarus [8]. The genus Caenagnathasia martinsoni was originally placed in this family, but it is probably more primitive, lying outside both Caenagnathidae and Oviraptoridae within the superfamily Caenagnathoidea.[9] Additionally, Maryańska, Osmólska, and Wołsan considered the oviraptorosaur with a pygostyle, Nomingia gobiensis, a member of this family.[10]
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, including a single foot named Macrophalangia canadensis[6], adding to the known fossil material.[8]
- Chirostenotes sternbergi, a more gracile caenagnathid. Some consider Elmisaurus elegans to be the same animal, as both are smaller and more slender than Chirostenotes pergracilis. It is also possible that this species represents a different gender of the larger C. pergracilis specimens.[4]
- Chirostenotes sp., a possible new species, has been identified from part of a lower jaw found in Montana, but not named.[9]
- Elmisaurus rarus, the only known Asian caenagnathid (excluding Caenagnathasia martinsoni), is known only from elements of the foot.[11]
- Elmisaurus elegans, a smaller Canadian species originally described as a species of Ornithomimus[12]. It may be the same species as Chirostenotes sternbergi[13], as noted above.
- The "Triebold caenagnathid", an infamous possible new species or genus collected by Triebold Paleontology of South Dakota. Known from two excellently preserved partial 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.
- Hagryphus giganteus, discovered most recently, is a fairly large and over-assuming yet seldom mentioned species from Upper Cretaceous beds in Colorado, USA (and is roughly the same age as Chirostenotes pergacilis.[14]
[edit] References
- ^ Sternberg, R.M. (1940). "A toothless bird from the Cretaceous of Alberta." Journal of Paleontology, 14(1): 81-85.
- ^ Clark, J. M., M. A. Norell, and T. Rowe. 2002. Cranial Anatomy of Citipati osmolskae (Theropoda, Oviraptorosauria), and a Reinterpretation of the Holotype of Oviraptor philoceratops. American Museum Novitates 3364: 1-24
- ^ Barsbold R., Osmolska, H., Watabe M., Currie, P. J., and Tsogtbaatar K. 2000. New oviraptorosaur (Dinosauria, Theropoda) from Mongolia: The first dinosaur with a pygostyle. Acta Palaeontologica Polonica 45 (2): 97-106).
- ^ a b Cracraft, J. (1971). "Caenagnathiformes: Cretaceous birds convergent in jaw mechanism to dicynodont reptiles." Journal of Paleontology, 45: 805-809.
- ^ 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).
- ^ a b Sternberg, C. H. 1932. Two new theropod dinosaurs from the Belly River Formation of Alberta. The Canadian Field-Naturalist 46: 99-105.
- ^ Currie, P.J. and Russell, D.A. 1988. Osteology and relationships of Chirostenotes pergracilis (Saurischia, Theropoda) from the Judith River Oldman Formation of Alberta. Canadian Journal of Earth Sciences -- Revue de Canadienne des Sciences de la Terre 25 (3): 972-986.
- ^ a b c Sues, H.-D. (1997). "On Chirostenotes, a Late Cretaceous oviraptorosaur (Dinosauria: Theropoda) from western North America." Journal of Vertebrate Paleontology, 17(4): 698-716.
- ^ a b 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.
- ^ Osmolska, H. 1981. Coosified tarsometatarsi in theropod dinosaurs and their bearing on the problem of bird origins. Paleontologia Polonica 42: 79-95.
- ^ Parks, W. A. 1933. New species of dinosaurs and turtles from the Belly River Formation of Alberta. University of Toronto Studies (Geological Series) 34: 1-33.
- ^ Currie, P.J. 1989. The first records of Elmisaurus (Saurischia, Theropoda) from North America. Canadian Journal of Earth Sciences -- Revue de Canadienne des Sciences de la Terre 26: 1319-1324.
- ^ Zanno, L. E. & Sampson, S. D. 2005. A new oviraptorosaur (Theropoda, Maniraptora) from the Late Cretaceous (Campanian) of Utah. Journal of Vertebrate Paleontology 25(4): 897-904.
