Alwalkeria

Taxobox
name = "Alwalkeria"
fossil_range = Late Triassic
regnum = Animalia
phylum = Chordata
classis = Sauropsida
superordo = Dinosauria
ordo = Saurischia
subordo = ?Theropoda
genus = "Alwalkeria"
genus_authority=Chatterjee & Creisler, 1994
subdivision_ranks=Species
subdivision=
*"A. maleriensis" (Chatterjee, 1986 [originally "Walkeria"] ) (type)

"Alwalkeria" (IPAEng|ælwɑːˈkɪərɪə; "for Alick Walker") is a genus of basal saurischian dinosaur from the Late Triassic of India. It was a small bipedal omnivore.

This dinosaur was originally named "Walkeria maleriensis" by Sankar Chatterjee in 1987, in honor of famous British paleontologist Alick Walker and the Maleri Formation, in which its fossils were found. However, the original generic name was found to be preoccupied by a bryozoan. A new name was created in 1994 by Chatterjee and Ben Creisler.

Remains of "Alwalkeria" have been recovered from the Maleri Formation of Andhra Pradesh, India. This is a Late Triassic geologic formation. Indeterminate prosauropod material has also been found in the Maleri, but "Alwalkeria" is the only named dinosaur species. The one known specimen is partial and consists of parts of the front ends of the upper and lower jaws, 28 incomplete vertebrae from all parts of the spinal column, most of a femur (thigh bone), and an astragalus (ankle bone). The partial skull is about 4 centimeters long (1.5 in).

Although material of "Alwalkeria" is limited, the spacing and shape of the teeth strongly resemble those of "Eoraptor". As in "Eoraptor", a gap separates the teeth of the premaxillary and the maxillary bones of the upper jaw. Other similarities in the skull of the two animals also link them on morphologic grounds (Langer 2004).

"Alwalkeria" has not been included in a cladistic analysis, but its similarities to "Eoraptor" suggest it may have held a similar position in the dinosaur family tree. However, the position of "Eoraptor" is disputed. One recent analysis finds it within the order Saurischia, but basal to the Theropoda-Sauropodomorpha split (Langer 2004). Paul Sereno finds instead that "Eoraptor" is a basal theropod (Sereno 1999). Others place "Eoraptor" outside of Dinosauria completely (Fraser "et al." 2002).

This dinosaur also has a "heterodont" dentition in the upper jaw, meaning that the teeth are differently shaped depending on their position within the jaw. Similarly to "Eoraptor" and basal sauropodomorphs, the front teeth are slender and straight, while the teeth in the sides of the jaw are curved backwards like those of predatory theropods, although none are serrated. This arrangement of teeth is neither clearly herbviorous nor clearly carnivorous, which suggests that this dinosaur was an omnivore with a varied diet, including insects, small vertebrates, and plant material.

Several features make "Alwalkeria" unique among basal dinosaurs. Besides its unserrated teeth, and the mandibular symphysis is proportionally wider than almost any other known dinosaur. Also, there is a very large articulation between the fibula and the ankle.

References

*Chatterjee, S. 1987. A new theropod dinosaur from India with remarks on the Gondwana-Laurasia connection in the Late Cretaceous. In: McKenzie, G.D. (Ed.). "Gondwana Six: Stratigraphy, Sedimentology, and Paleontology. Geophysical Monograph 41". Washington, D.C.: American Geophysical Union. Pp. 183-189.
*Chatterjee, S. & Creisler, B.S. 1994. "Alwalkeria" (Theropoda) and "Murturneria" (Plesiosauria), new names for preoccupied "Walkeria" Chatterjee, 1987, and "Turneria" Chatterjee and Small, 1989. "Journal of Vertebrate Paleontology" 14(1): 142.
*Fraser, N.C., Padian, K., Walkden, G.M., & Davis, A.L.M. 2002. Basal dinosauriform remains from Britain and the diagnosis of the Dinosauria. "Palaeontology" 45(1): 79-95.
*Langer, M.C. 2004. Basal Saurischia. In: Weishampel, D.B., Dodson, P., & Osmolska, H. (Eds.). "The Dinosauria" (2nd Edition). Berkeley: University of California Press. Pp. 25-46.
*Norman, D.B. 1990. Problematic Theropods: Coelurosaurs. In: Weishampel, D.B., Dodson, P. & Osmolska, H. (Eds.). "The Dinosauria" (1st Edition). Berkeley: University of California Press. Pp. 280-305.
*Remes, K. and Rauhut, O. W. M. 2005. The oldest Indian dinosaur Alwalkeria maleriensis Chatterjee revised: a chimera including remains of a basal saurischian; p. 218 in Kellner, A. W . A., Henriques, D .D. R. and Rodrigues, T. (eds.), II Congresso Latino-Americano de Paleontologie de Vertebrados. Boletim de Resumos. Museu Nacional, Rio de Janeiro.
*Sereno, P.C. 1999. The evolution of dinosaurs. "Science" 284: 2137-2147.

External links

* [http://www.dinodata.org/index.php?option=com_content&task=view&id=6011&Itemid=67 "Alwalkeria"] at Dinodata (text copied from "The Dinosauria", First Edition, as "Walkeria")
* [http://www.dinosaurier-web.de/galery/pages_a/alwalkeria.html "Alwalkeria"] at [http://www.dinosaurier-web.de Dinosaurier-Web] (including Picture, in German)