|Holotype saurischian femur in multiple views|
Chatterjee & Creisler, 1994
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.
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 50 cm (1.6 ft) long. Gregory S. Paul estimated its weight at 2 kg and length at 1.5 m in 2010.
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.
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 is disputed, with one analysis finding it within the order Saurischia, but basal to the Theropoda-Sauropodomorpha split (Langer 2004). Paul Sereno insisted that Eoraptor was a basal theropod. Others place Eoraptor outside of Dinosauria completely.
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.
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.
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.
Alick Donald Walker (26 October 1925 – 4 December 1999) was a British palaeontologist, after whom the Alwalkeria genus of dinosaur is named.
He was born in Skirpenbeck, near York and attended Pocklington School from 1936 to 1943. He began a degree course in engineering at Cambridge, but dropped out in 1944. In 1948 he returned to university after national service, reading Geology at the University of Bristol. On graduation, he join the research group of Professor Stanley Westoll at the University of Newcastle upon Tyne, working on the fossil reptiles of the Late Triassic found in Elgin. He was appointed Lecturer in Geology in 1954, while working on his PhD.
The bony remains of the Elgin reptile fossils were poor, sometimes just indentations in rocks. Walker devised a new casting method to capture the anatomical information in these fossils, using PVC; many of the resulting casts are now in the National Museum of Scotland and the Natural History Museum. His early work was also notable for reclassifying and naming the English theropod dinosaurs Eustreptospondylus and Metriacanthosaurus.
In the late 1960s Walker studied the origin of crocodilians and of birds, which became controversial in 1972 with his publication of a paper in Nature arguing for a close relationship between sphenosuchian crocodylomorphs and birds. He later accepted that this hypothesis might be incorrect in a 1985 paper on Archaeopteryx.Averostra
Averostra, or "bird snouts", is a clade that includes most theropod dinosaurs that have a promaxillary fenestra (fenestra promaxillaris), an extra opening in the front outer side of the maxilla, the bone that makes up the upper jaw. Two groups of averostrans, the Ceratosauria and the Orionides, survived into the Cretaceous period. When the Cretaceous–Paleogene extinction event occurred, ceratosaurians and two groups of orionideans within the clade Coelurosauria, the Tyrannosauroidea and Maniraptoriformes, were still extant. Only one subgroup of maniraptoriformes, Aves, survived the extinction event and persisted to the present day.Avetheropoda
Avetheropoda, or "bird theropods", is a clade that includes carnosaurians and coelurosaurs to the exclusion of other dinosaurs.Cerapoda
Cerapoda ("ceratopsians and ornithopods") is a clade of the dinosaur order Ornithischia.Dinosauriformes
Dinosauriformes is a clade of archosaurian reptiles that include the dinosaurs and their most immediate relatives. All dinosauriformes are distinguished by several features, such as shortened forelimbs and a partially to fully perforated acetabulum, the hole in the hip socket traditionally used to define dinosaurs. The oldest known member is Asilisaurus, dating to about 245 million years ago in the Anisian age of the middle Triassic period.Haya griva
Haya is an extinct genus of basal neornithischian dinosaur known from Mongolia.Herrerasauridae
Herrerasauridae is a family of carnivorous basal saurischian dinosaurs. They are among the oldest known dinosaurs, first appearing in the fossil record around 233.23 million years ago (Late Triassic), before becoming extinct by the end of the Triassic period. Herrerasaurids were relatively small-sized dinosaurs, normally not more than 4 metres (13 ft) long. The best known representatives of this group are from South America (Brazil, Argentina), where they were first discovered in the 1960s. A nearly complete skeleton of Herrerasaurus ischigulastensis was discovered in the Ischigualasto Formation in San Juan, Argentina, in 1988. Less complete herrerasaurids have been found in North America, and they may have inhabited other continents as well.
Herrerasaurid anatomy is unusual and specialized, and they are not considered to be ancestral to any later dinosaur group. They only superficially resemble theropods and often present a mixture of very primitive and derived traits. The acetabulum is only partly open, and there are only two sacral vertebrae, the lowest number among dinosaurs. The pubic bone has a derived structure, being rotated somewhat posteriorly and folded to create a superficially tetanuran-like terminal expansion, especially prominent in H. ischigulastensis. The hand is primitive in having five metacarpals and the third finger longer than the second, but resembles those of theropods in having only three long fingers, with curved claws. Herrerasaurids also have a hinged mandible, which is also found in theropods.Jeholosauridae
Jeholosaurids were herbivorous neornithischian dinosaurs from the Cretaceous Period (Aptian - Santonian, with a possible Campanian record) of Asia. The family was first proposed by Han et al. in 2012. The jeholosaurids were defined as those ornithischians more closely related to Jeholosaurus shangyuanensis than to Hypsilophodon foxii, Iguanodon bernissartensis, Protoceratops andrewsi, Pachycephalosaurus wyomingensis, or Thescelosaurus neglectus. The Jeholosauridae includes the type genus Jeholosaurus and Yueosaurus.Jingshanosaurus
Jingshanosaurus (meaning "Jingshan lizard") is a genus of sauropodomorph dinosaurs from the early Jurassic period.Lower Maleri Formation
The Lower Maleri Formation is a sedimentary rock formation found in Andhra Pradesh and Telangana, India. It is the lowermost member of the Pranhita–Godavari Basin. It is of late Carnian to early Norian age (Upper Triassic), and is notable for its fossils of early dinosaurs, including the basal saurischian (possible theropod) Alwalkeria.Maleri Formation
The Maleri Formation is a sedimentary rock formation found in Andhra Pradesh, India. It is of Norian age (Upper Triassic), and is notable for its fossils of early dinosaurs, including the basal saurischian (possible theropod) Alwalkeria.Neotheropoda
Neotheropoda (meaning "new theropods") is a clade that includes coelophysoids and more advanced theropod dinosaurs, and the only group of theropods who survived the Triassic–Jurassic extinction event. Yet all of the neotheropods became extinct during the early Jurassic period except for Averostra.Orionides
Orionides is a clade of tetanuran theropod dinosaurs from the Middle Jurassic to the Present. The clade includes most theropod dinosaurs, including birds.Orodrominae
Orodrominae is a subfamily of parksosaurid dinosaurs from the Cretaceous of North America and Asia.Riojasauridae
Riojasauridae is a family of sauropod-like dinosaurs from the Upper Triassic. It is known primarily from the genera Riojasaurus and Eucnemesaurus. Sites containing Riojasauridae include the Lower Elliot Formation of Orange Free State, South Africa (where fossils of Eucnemesaurus have been found), and Ischigualasto, in La Rioja Province, Argentina ( where fossils of Riojasaurus have been recovered).Saurischia
Saurischia ( saw-RIS-kee-ə, meaning "reptile-hipped" from the Greek sauros (σαῦρος) meaning 'lizard' and ischion (ἴσχιον) meaning 'hip joint') is one of the two basic divisions of dinosaurs (the other being Ornithischia). ‘Saurischia’ translates to lizard-hipped.
In 1888, Harry Seeley classified dinosaurs into two orders, based on their hip structure, though today most paleontologists classify Saurischia as an unranked clade rather than an order.Unaysauridae
Unaysauridae is a family of basal sauropodomorphs from the Late Triassic of India and Brazil.Xixiposaurus
Xixiposaurus is a genus of prosauropod dinosaur which existed in what is now Lower Lufeng Formation, China during the lower Jurassic period. It was first named by Sekiya Toru in 2010 and the type species is Xixiposaurus suni.Yueosaurus
Yueosaurus is an extinct genus of basal ornithopod dinosaur known from Zhejiang Province, China.