Caudipteryx

''Caudipteryx'' (which means "tail feather") is a genus of peacock-sized theropod dinosaurs that lived in the Barremian age of the early Cretaceous (about 124.6 million years ago). They were feathered and extremely birdlike in their overall appearance, to the point that some paleontologists think it was a bird. Two species have been described: ''C. zoui'' (the type species), in 1998, and ''C. dongi'', in 2000.

''Caudipteryx'' fossils were first discovered in the Yixian Formation of the Sihetun area of Liaoning Province, northeastern China in 1997.

Description

''Caudipteryx'', like many other maniraptorans, has a mix of reptile- and bird-like anatomical features.Witmer, L.M. (2005). “The Debate on Avian Ancestry; Phylogeny, Function and Fossils”, ''Mesozoic Birds: Above the Heads of Dinosaurs'' : 3–30.

It had a short, boxy skull with a beak-like snout that retained only a few tapered teeth in the front of the upper jaw. It had a stout trunk, long legs and was probably a swift runner.

Its short tail was stiffened toward the tip, with few vertebrae, like in birds and other oviraptorosaurs. It has a primitive pelvis and shoulder, and primitive skull details in the quadratojugal, squamosal, quadrate, jugal, and mandibular fenestra (in the cheek, jaw, and jaw joint). It has a hand skeleton with a reduced third finger, like that of early birds and the oviraptorid '' Heyuannia''.Osmolska, H., Currie, P.J., and Barsbold, R. (2004). "Oviraptorosauria." In Weishampel, Dodson, Osmolska (eds.) ''The Dinosauria'', second edition. University of California Press, 2004.

''Caudipteryx'' had uncinate processes on the ribs, birdlike teeth, a first toe which may or may not be partially reversed and overall body proportions that are comparable to those of modern flightless birds.PDF
/ref> The size of ''C. zoui'' is estimated at 65 cm (2.1 ft) in length and 2.2 kg (4.8 lbs) in body mass, while ''C. dongi'' is thought to have been slightly larger at 80 cm (2.6 ft) in length and 2.3 kg (5 lbs) in body mass.

Paleobiology

Feathers

The hands of ''Caudipteryx'' supported symmetrical, pennaceous feathers that had vanes and barbs, measuring between long. The primary feathers were arranged in a wing-like fan along the second finger, just like primary feathers of birds and other maniraptorans. No fossil of ''Caudipteryx zoui'' preserves any secondary feathers attached to the forearms, as found in dromaeosaurids, ''Archaeopteryx,'' and modern birds. Either these arm feathers are not preserved, or they were not present on ''Caudipteryx'' in life. An additional fan of feathers existed on its tail. The shortness and symmetry of the feathers, and the shortness of the arms relative to the body size, indicate that ''Caudipteryx'' was flightless.

Its body was covered in black feathers, with a visible banding pattern preserved on tail feathers.

Diet

''Caudipteryx'' is thought to have been an omnivore. In at least two specimens of ''Caudipteryx'' (NGMC 97 4 A and NGMC 97 9 A), gastroliths are preserved. As in some herbivorous dinosaurs, the avialan '' Sapeornis'', and modern birds, these gastroliths remain in the position where the animals' gizzards would have been.

Paleoecology

All ''Caudipteryx'' fossils were recovered from the Yixian Formation in Liaoning, China. Specifically, they come from a small area of the Jianshangou bed, near the town of Zhangjiakou. They appear to have been fairly common, though isolated to this small region. The specific region in which ''Caudipteryx'' lived was home to the other feathered dinosaurs '' Dilong'' and '' Sinornithosaurus''.

Implications

The discovery of ''Caudipteryx'' has led to many intensive studies and debate over the relationship of birds and dinosaurs. The possible positions in the debate can be summarized as follows: ''Caudipteryx'' is either a member of the Oviraptorosauria, or a bird, or both, and birds are either dinosaurs or they are not. (See the rest of this section and Phylogeny, below).

Because ''Caudipteryx'' has clear and unambiguously pennaceous feathers, like modern birds, and because several cladistic analyses have consistently recovered it as a non-avian oviraptorid dinosaur, it provided, at the time of its description, the clearest and most succinct evidence that birds evolved from dinosaurs. Lawrence Witmer stated:
“The presence of unambiguous feathers in an unambiguously non-avian theropod has the rhetorical impact of an atomic bomb, rendering any doubt about the theropod relationships of birds ludicrous.”

However, not all scientists agreed that ''Caudipteryx'' was unambiguously non-avian, and some of them continued to doubt that general consensus. Paleornithologist Alan Feduccia sees ''Caudipteryx'' as a flightless bird evolving from earlier archosaurian dinosaurs rather than from late theropods.Feduccia, A. (1999). ''The Origin and Evolution of Birds''. 420 pp. Yale University Press, New Haven. . Jones ''et al.'' (2000) found that ''Caudipteryx'' was a bird based on a mathematical comparison of the body proportions of flightless birds and non-avian theropods. Dyke and Norell (2005) criticized this result for flaws in their mathematical methods, and produced results of their own which supported the opposite conclusion.

Other researchers not normally involved in the debate over bird origins, such as Zhou, acknowledged that the true affinities of ''Caudipteryx'' were debatable.

Classification

The consensus view, based on several cladistic analyses, is that ''Caudipteryx'' is a basal (primitive) member of the Oviraptorosauria, and the oviraptorosaurians are non-avian theropod dinosaurs. '' Incisivosaurus'' is the only oviraptorosaur that is more primitive.

Halszka Osmólska ''et al.'' (2004) ran a cladistic analysis that came to a different conclusion. They found that the most birdlike features of oviraptorids actually place the whole clade within Aves itself, meaning that ''Caudipteryx'' is both an oviraptorid and a bird. In their analysis, birds evolved from more primitive theropods, and one lineage of birds became flightless, re-evolved some primitive features, and gave rise to the oviraptorids. This analysis was persuasive enough to be included in paleontological textbooks like Benton's ''Vertebrate Paleontology'' (2005).Osmólska, Halszka, Currie, Philip J., Barsbold, Rinchen (2004) ''The Dinosauria'' Weishampel, Dodson, Osmolska. "Chapter 8 Oviraptorosauria" University of California Press.
The view that ''Caudipteryx'' was secondarily flightless is also preferred by Gregory S. Paul,Paul, G.S. (2002). ''Dinosaurs of the Air: The Evolution and Loss of Flight in Dinosaurs and Birds.'' Johns Hopkins University Press, Baltimore. Lü ''et al.'',Lü, J., Dong, Z., Azuma, Y., Barsbold, R., and Tomida, Y. (2002). "Oviraptorosaurs compared to birds." In Zhou, Z., and Zhang, F. (eds.), ''Proceedings of the 5th Symposium of the Society of Avian Paleontology and Evolution'', 175–189. Beijing Science Press. and Maryańska ''et al.''

Others, such as Stephen Czerkas and Larry Martin have concluded that ''Caudipteryx'' is not a theropod dinosaur at all. They believe that ''Caudipteryx'', like all maniraptorans, is a flightless bird, and that birds evolved from non-dinosaurian archosaurs.

See also

* Timeline of oviraptorosaur research

References

External links

* Australian Museum
Chinese Dinosaurs: ''Caudipteryx zoui''
Retrieved 2007-FEB-19.
* Natural History Museum of Los Angeles County

Retrieved 2007-FEB-19.
* Research Casting International
Life-size model of ''Caudipteryx zoui''
Retrieved 2007-FEB-19.
* CNN
Scientists: Fossils prove that birds evolved from dinosaurs
Retrieved 2007-AUG-10

{{Taxonbar, from=Q131069

Oviraptorosaurs
Feathered dinosaurs
Early Cretaceous dinosaurs of Asia
Fossils of China
Fossil taxa described in 1998
Taxa named by Philip J. Currie
Taxa named by Mark Norell
Yixian fauna