Alwalkeria is a genus of basal saurischian dinosaur from the Late Triassic of India.
It was a small bipedal omnivore.
Etyomology This dinosaur was originally named Walkeria
maleriensis by Sankar Chatterjee in 1987, in honor of famous British paleontologist
Alick Walker. 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, Alwalkeria. The species
name maleriensis is a reference to the Maleri Formation, in India, where its fossils were
found. Description
The only known specimen, holotype ISI R306 is incomplete 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, and an astragalus. The partial skull is about 4 centimeters
long. 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 morphological grounds. Estimates suggest that Alwalkeria was at best
50 cm long. Dentition and diet
This dinosaur also has a heterodont dentition in the upper jaw, meaning that the teeth are
differently shaped depending on their position in 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 of these
teeth are serrated. This arrangement of teeth is neither clearly herbivorous nor clearly
carnivorous, which suggests that this dinosaur was an omnivore with a varied diet, including
insects, small vertebrates, and plant material. Rauhut and Remes found Alwalkeria to be a
chimaera, with the anterior skull referable to a crurotarsan, and the vertebrae referable
to other ancient reptiles. The femur and the astragalus are clearly dinosaurian however,
with the latter possessing saurischian characteristics. Classification and phylogeny
Chatterjee 1987 originally described Alwalkeria as a basal theropod. In 1996, Loyal et al.
agreed with this classification. Paul 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 and Martínez and Alcober, observed that Alwalkeria was too
primitive to be a theropod and considered it a basal saurischian. The current scientific
consensus is that this genus does indeed occupy a basal position within Saurischia.
Relation to Eoraptor 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, with one
analysis finding it within the order Saurischia, but basal to the Theropoda-Sauropodomorpha
split. Paul Sereno instead that Eoraptor is a basal theropod. Others place Eoraptor outside
of Dinosauria completely. Distinguishing anatomical features
A diagnosis is a statement of the anatomical features of an organism that collectively
distinguish it from all other organisms. Some, but not all, of the features in a diagnosis
are also autapomorphies. An autapomorphy is a distinctive anatomical feature that is unique
to a given organism or group. According to Chatterjee Alwalkeria can be
distinguished based on the following characteristics: an excavation is present in the bases of the
dorsal neural arches the presence of a highly expanded femoral
head the fourth trochanter is very prominent
Several features make Alwalkeria unique among basal dinosaurs, such as its lack of serrated
teeth, the mandibular symphysis being proportionally wider than almost any other known dinosaur,
and there is a very large articulation between the fibula and the ankle.
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. Indeterminate prosauropod material has been
found in the Maleri Formation, and Alwalkeria is the only named dinosaur species from this
locality. References
Chatterjee, S. & Creisler, B.S. 1994. Alwalkeria and Murturneria, 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.. The Dinosauria. 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., II Congresso Latino-Americano de Paleontologie de Vertebrados. Boletim de Resumos. Museu
Nacional, Rio de Janeiro. External links
Alwalkeria at Dinodata Alwalkeria at Dinosaurier-Info