Alwalkeria Maleriensis

''Alwalkeria'' (; "for Alick Walker") is an extinct genus of basal saurischian dinosaur from the Late Triassic Lower Maleri Formation of India.

Discovery and naming

''Alwalkeria'' was originally named ''Walkeria maleriensis'' by Sankar Chatterjee in 1987, in honor of British paleontologist Alick Walker. However, since the original generic name was found to be preoccupied by a bryozoan, the name ''Alwalkeria'' was created in 1994 by Chatterjee and Ben Creisler: the specific name ''maleriensis'' is a reference to the Lower Maleri Formation, in southern India, where its fossils were found.

In 2005, Rauhut and Remes found ''Alwalkeria'' to be a chimera, with the anterior skull referable to a crurotarsan, and the vertebrae referable to various other ancient reptiles including Prolacertiformes; the femur and the astragalus are clearly dinosaurian, however, with the latter possessing saurischian characteristics. In 2011, Novas and colleagues argued that ''Alwalkeria'' remains valid on the basis of an unusual morphology of its femur and an astragalus with a conservative morphology more similar to that of basal dinosaurs. In 2016, Lecuona, Ezcurra & Irmis reiterated the chimaeric nature of the ''Alwalkeria'' holotype, noting that the skull material could be referred to the Crocodylomorpha. They also observed that the distal femur was more consistent with the morphology of pseudosuchians, leading them to identify this bone fragment as an indeterminate representative of that clade. The vertebrae lack anatomical features allowing for a precise identification, dinosaur, pseudosuchian, or otherwise.

Description

The only known specimen, holotype ISI R306 is incomplete and chimaeric, consisting of parts of multiple animals, including the front ends of the upper and lower jaws, 28 incomplete vertebrae from all parts of the spinal column, most of a femur, and an astragalus (ankle bone). The partial skull—likely belonging to a crocodylomorph—is about long. ''Alwalkeria'' would have measured around long and weighed up to .

Classification and phylogeny

Chatterjee 1987 originally described ''Alwalkeria'' as a basal theropod. In 1996, Loyal et al. agreed with this classification. Paul (1988) understood ''Alwalkeria'' as a link between herrerasaurids and the genus ''Protoavis'', and hence assigned it to Herrerasauridae based on features of the femur. However Langer (2004) and Martínez and Alcober (2009), observed that ''Alwalkeria'' was too primitive to be a theropod and considered it a basal saurischian.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. The current scientific consensus is that this genus, or at least its hindlimb, does indeed occupy a basal position within Saurischia.

''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'' was formerly disputed, with one analysis finding it within the order Saurischia, but basal to the Theropoda-Sauropodomorpha split. Paul Sereno insisted that ''Eoraptor'' was a basal theropod.

Distinguishing anatomical features

According to Chatterjee (1987) ''Alwalkeria'' can be distinguished based on the following characteristics: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.
* an excavation is present in the bases of the dorsal neural arches (debated because the vertebrae likely don't belong to ''Alwalkeria'')
* the presence of a highly expanded femoral head
* the fourth trochanter is very prominent

Paleoecology

Provenance and occurrence

The only known specimen of ''Alwalkeria'' was recovered in the Godavari Valley locality from the Maleri Formation of Andhra Pradesh, India. The remains were collected by S. Chatterjee in 1974 in red mudstone that was deposited during the Carnian stage of the Triassic period, approximately 235 to 228 million years ago. The specimen is housed in the collection of the Indian Statistical Institute, in Kolkata, India.

Fauna and habitat

The Maleri Formation has been interpreted as being the site of an ancient lake or river. Material of the sauropodomorphs ''Jaklapallisaurus'' and ''Nambalia'' and the herrerasaurian ''Maleriraptor'' have been found in the Upper Maleri Formation, as well as intermediate prosauropod remains.

References

Bibliography

* 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.
* Chatterjee, S. & Creisler, B.S. 1994. ''Alwalkeria'' (Theropoda) and ''Morturneria'' (Plesiosauria), new names for preoccupied ''Walkeria'' Chatterjee, 1987, and ''Turneria'' Chatterjee and Small, 1989. ''Journal of Vertebrate Paleontology'' 14(1): 142.
* 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.

External links

''Alwalkeria''
a
Dinosaurier-Info
(in German)

{{Taxonbar, from=Q133238

Saurischia
Dinosaur genera
Carnian dinosaurs
Dinosaurs of India
Fossil taxa described in 1994
Taxa named by Sankar Chatterjee