Alwalkeria
Alwalkeria (; "for Alick Walker") is a genus of basal saurischian dinosaur from the Late Triassic, living in India. It was a small bipedal omnivore. Etymology. This dinosaur 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 species name "maleriensis" is a reference to the Maleri Formation, in southern 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 (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 morphological grounds. Estimates suggest that "Alwalkeria" was  at best long. Gregory S. Paul estimated its weight at 2 kg and length at 1.5 m in 2010. Dentition and diet. This dinosaur also had "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 (2005) found "Alwalkeria" to be a chimera, 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 (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. The current scientific consensus is that this genus 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. A diagnosis is a statement of the anatomical features of an organism (or group) 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 (1987) "Alwalkeria" can be distinguished based on the following characteristics: 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. Material of the prosauropods  Jaklapallisaurus and "Nambalia" have been found in the Maleri Formation, as well as intermediate prosauropod remains, and "Alwalkeria" is the only named carnivorous dinosaur species from this locality.