Caudipteryx

Taxobox
name = "Caudipteryx"
fossil_range = Early Cretaceous


image_width = 250px
image_caption = "Caudipteryx zoui" fossil replica displayed in the Hong Kong Science Museum.
regnum = Animalia
phylum = Chordata
classis = Sauropsida
superordo = Dinosauria
ordo = Saurischia
subordo = Theropoda
infraordo = Oviraptorosauria
familia = Caudipteridae
genus = "Caudipteryx"
genus_authority = Ji "et al.", 1998
subdivision_ranks = Species
subdivision ="C. zoui" Ji "et al.", 1998 (type)
"C. dongi" Zhou & Wang, 2000

"Caudipteryx" (which means "tail feather") is a genus of peacock-sized theropod dinosaurs that lived in the Barremian age of the early Cretaceous Period (about 127 million years ago). They were feathered and remarkably birdlike in their overall appearance.Ji, Q., Currie, P.J., Norell, M.A., and Ji, S. (1998). "Two feathered dinosaurs from northeastern China." "Nature", 393(6687): 753–761. DOI|10.1038/31635 [http://www.biology.ualberta.ca/faculty/philip_currie/uploads/pdfs/1998/1998Caudipteryx.pdf PDF fulltext] ] 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.

Anatomy

"Caudipteryx", like many other maniraptorans, has an interesting 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. ISBN 0-520-20094-2]

"Caudipteryx" 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. On the hands it had symmetrical, pennaceous, feathers that had vanes and barbs, and that measured between 15–20 centimeters (6–8 inches). These 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" 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 short tail. The shortness and symmetry of the feathers, and the shortness of the arms relative to the body size, indicate that "Caudipteryx" could not fly."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. "Caudipteryx" has a short, distally stiffened, tail 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 primitive birds and the oviraptorid "Ingenia".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.Zhou, Z., Wang, X., Zhang, F., and Xu, X. (2000). "Important features of "Caudipteryx" - Evidence from two nearly complete new specimens." "Vertebrata Palasiatica", 38(4): 241–254. [http://www.ivpp.ac.cn/pdf/magazine232.pdf PDF fulltext] ] Zhou, Z., and Wang, X. (2000). "A new species of "Caudipteryx" from the Yixian Formation of Liaoning, northeast China." "Vertebrata Palasiatica", 38(2): 113–130. [http://www.ivpp.ac.cn/pdf/magazine213.pdf PDF fulltext] ] Jones, T.D., Farlow, J.O., Ruben, J.A., Henderson, D.M., and Hillenius, W.J. (2000). "Cursoriality in bipedal archosaurs." "Nature", 406(6797): 716–718. DOI|10.1038/35021041 [http://arnica.csustan.edu/jones/Publications/pdf/Cursoriality.pdf PDF fulltext] [http://www.nature.com/nature/journal/v406/n6797/suppinfo/406716a0.html Supplementary information] ]

Implications

The discovery of "Caudipteryx" led to many intensive studies on 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 nonavian, 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 nonavian 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.A paleontologist like Alan Feduccia, who opposes the theory that birds are theropods, sees "Caudipteryx" as a flightless bird unrelated to dinosaurs.Feduccia, A. (1999). "The Origin and Evolution of Birds". 420 pp. Yale University Press, New Haven. ISBN 0300078617.] 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.Jones, T.D., Farlow, J.O., Ruben, J.A., Henderson, D.M., and Hillenius, W.J. (2000). "Cursoriality in bipedal archosaurs." "Nature", 406(6797): 716–718. DOI|10.1038/35021041 [http://arnica.csustan.edu/jones/Publications/pdf/Cursoriality.pdf PDF fulltext] [http://www.nature.com/nature/journal/v406/n6797/suppinfo/406716a0.html Supplementary information] ] Dyke, G.J., and Norell, M.A. (2005). "Caudipteryx" as a non-avialan theropod rather than a flightless bird." "Acta Palaeontologica Polonica", 50(1): 101–116. [http://www.app.pan.pl/acta50/app50-101.pdf PDF fulltext] ]

Other researchers not normally involved in the debate over bird origins, such as Zhou, acknowledged that the true affinities of "Caudipteryx" were debatable.Zhou, Z., Wang, X., Zhang, F., and Xu, X. (2000). "Important features of "Caudipteryx" - Evidence from two nearly complete new specimens." "Vertebrata Palasiatica", 38(4): 241–254. [http://www.ivpp.ac.cn/pdf/magazine232.pdf PDF fulltext] ]

Phylogenetic position

The consensus view, based on several cladistic analyses, is that "Caudipteryx" is a basal (primitive) member of the Oviraptoridae, and the oviraptorids are nonavian theropod dinosaurs.Dyke, Gareth J., Norell, Mark A. (2005). "Caudipteryx" as a non-avialan theropod rather than a flightless bird". "Acta Palaeontologica Polonica", 50(1):101–116.] "Incisivosaurus" is the only oviraptorid that is more primitive.cite journal |last=Turner |first=Alan H. |coauthors= Pol, Diego; Clarke, Julia A.; Erickson, Gregory M.; and Norell, Mark |year=2007 |title=A basal dromaeosaurid and size evolution preceding avian flight |url=http://www.sciencemag.org/cgi/reprint/317/5843/1378.pdf |format=pdf |journal=Science |volume=317 |pages=1378–1381 |doi=10.1126/science.1144066 |pmid=17823350 ]

Halszka Osmolska "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 analyis was persuasive enough to be included in paleontological textbooks like Benton's "Vertebrate Paleontology" (2005).Osmolska, 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. ISBN 0801867630] 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 Maryanska "et al".Maryanska, T., Osmólska, H., and Wolsam, M. (2002). "Avialian status for Oviraptorosauria." "Acta Palaeontologica Polonica", 47(1): 97–116. [http://app.pan.pl/acta47/app47-097.pdf PDF fulltext] ]

Others, such as Stephen Czerkas and Larry Martin have concluded that "Caudipteryx" is not a theropod dinosaur at all.Martin, Larry D.,(2004) “A basal archosaurian origin for birds”, "Acta Zoologica Sinica" 50(6):978–990] They believe that "Caudipteryx", like all maniraptorans, is a flightless bird, and that birds evolved from non-dinosaurian archosaurs.Martin, L.D., and Czerkas, S.A. (2000). "The Fossil Record of Feather Evolution in the Mesozoic." "American Zoologist", 40(4): 687–694. [http://icb.oxfordjournals.org/cgi/reprint/40/4/687.pdf PDF fulltext] ]

References

External links

* Australian Museum: [http://www.amonline.net.au/chinese_dinosaurs/factsheets/13.htm Chinese Dinosaurs: "Caudipteryx zoui"] . Retrieved 2007-FEB-19.
* Dino Russ's Lair: [http://www.dinoruss.com/jim-robins-art/Caudipteryx.gif"Caudipteryx" reconstruction] by paleoartist Jim Robins. Retrieved 2007-FEB-19.
* Natural History Museum of Los Angeles County: [http://www.nhm.org/journey/prehist/birds/caudipteryx.html From Dinosaurs to Birds: "Caudipteryx"] . Retrieved 2007-FEB-19.
* Research Casting International: [http://www.rescast.com/specimens/show_specimen.php?SpecimenID=163 Life-size model of "Caudipteryx zoui"] . Retrieved 2007-FEB-19.
* CNN: [http://www.cnn.com/TECH/science/9806/23/feathered.dinosaur/ Scientists: Fossils prove that birds evolved from dinosaurs] . Retrieved 2007-AUG-10