''Alwalkeria'' (; "for Alick Walker") is a

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...

partly based on basal saurischian

dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is t ...

remains from the

Late Triassic The Late Triassic is the third and final epoch of the Triassic Period in the geologic time scale, spanning the time between Ma and Ma (million years ago). It is preceded by the Middle Triassic Epoch and followed by the Early Jurassic Epoch ...

, living in

India India, officially the Republic of India (Hindi: ), is a country in South Asia. It is the List of countries and dependencies by area, seventh-largest country by area, the List of countries and dependencies by population, second-most populous ...

. A thighbone found indicates a small

bipedal Bipedalism is a form of terrestrial locomotion where an organism moves by means of its two rear limbs or legs. An animal or machine that usually moves in a bipedal manner is known as a biped , meaning 'two feet' (from Latin ''bis'' 'double' ...

form. It has been seen as a chimera.

Etymology

This taxon was originally named ''Walkeria maleriensis'' by

Sankar Chatterjee Sankar Chatterjee (born May 28, 1943) is a paleontologist, and is the Paul W. Horn Professor of Geosciences at Texas Tech University and Curator of Paleontology at the Museum of Texas Tech University. He earned his Ph. D. from the University o ...

in 1987, in honor of British

paleontologist Paleontology (), also spelled palaeontology or palæontology, is the scientific study of life that existed prior to, and sometimes including, the start of the Holocene epoch (roughly 11,700 years before present). It includes the study of fossi ...

Alick Walker 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 ...

. However, since the original generic name was found to be

preoccupied The Botanical and Zoological Codes of nomenclature treat the concept of synonymy differently. * In botanical nomenclature, a synonym is a scientific name that applies to a taxon that (now) goes by a different scientific name. For example, Linnae ...

by a

bryozoa Bryozoa (also known as the Polyzoa, Ectoprocta or commonly as moss animals) are a phylum of simple, aquatic invertebrate animals, nearly all living in sedentary colonies. Typically about long, they have a special feeding structure called a ...

n, the name ''Alwalkeria'' was created in 1994 by Chatterjee and Ben Creisler. The specific name ''maleriensis'' is a reference to the Maleri Formation, in southern India, where its

fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...

s were found.

Description

The only known specimen,

holotype A holotype is a single physical example (or illustration) of an organism, known to have been used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of seve ...

ISI R306 is incomplete and consists of parts of the front ends of the upper and lower jaws, 28 incomplete

vertebra The spinal column, a defining synapomorphy shared by nearly all vertebrates, Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characteristi ...

e from all parts of the

spinal column The vertebral column, also known as the backbone or spine, is part of the axial skeleton. The vertebral column is the defining characteristic of a vertebrate in which the notochord (a flexible rod of uniform composition) found in all chordates ...

, most of a

femur The femur (; ), or thigh bone, is the proximal bone of the hindlimb in tetrapod vertebrates. The head of the femur articulates with the acetabulum in the pelvic bone forming the hip joint, while the distal part of the femur articulates ...

, and an astragalus (ankle bone). The partial

skull The skull is a bone protective cavity for the brain. The skull is composed of four types of bone i.e., cranial bones, facial bones, ear ossicles and hyoid bone. However two parts are more prominent: the cranium and the mandible. In humans, th ...

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 ''Eoraptor'' () is a genus of small, lightly built, basal sauropodomorph. One of the earliest-known dinosaurs, it lived approximately 231 to 228 million years ago, during the Late Triassic in Western Gondwana, in the region that is now northw ...

''. As in ''Eoraptor'', a gap separates the teeth of the

premaxilla The premaxilla (or praemaxilla) is one of a pair of small cranial bones at the very tip of the upper jaw of many animals, usually, but not always, bearing teeth. In humans, they are fused with the maxilla. The "premaxilla" of therian mammal has ...

ry and the

maxilla The maxilla (plural: ''maxillae'' ) in vertebrates is the upper fixed (not fixed in Neopterygii) bone of the jaw formed from the fusion of two maxillary bones. In humans, the upper jaw includes the hard palate in the front of the mouth. T ...

ry 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

The holotype had

heterodont In anatomy, a heterodont (from Greek, meaning 'different teeth') is an animal which possesses more than a single tooth morphology. In vertebrates, heterodont pertains to animals where teeth are differentiated into different forms. For exampl ...

dentition Dentition pertains to the development of teeth and their arrangement in the mouth. In particular, it is the characteristic arrangement, kind, and number of teeth in a given species at a given age. That is, the number, type, and morpho-physiolo ...

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

predator Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not kill t ...

y theropods, although none of these teeth are serrated. This arrangement of teeth is neither clearly

herbivorous A herbivore is an animal anatomically and physiologically adapted to eating plant material, for example foliage or marine algae, for the main component of its diet. As a result of their plant diet, herbivorous animals typically have mouthpar ...

nor clearly

carnivorous A carnivore , or meat-eater (Latin, ''caro'', genitive ''carnis'', meaning meat or "flesh" and ''vorare'' meaning "to devour"), is an animal or plant whose food and energy requirements derive from animal tissues (mainly muscle, fat and other ...

, which suggests that the jaws were from an

omnivore An omnivore () is an animal that has the ability to eat and survive on both plant and animal matter. Obtaining energy and nutrients from plant and animal matter, omnivores digest carbohydrates, protein, fat, and fiber, and metabolize the nu ...

with a varied diet, including

insect Insects (from Latin ') are pancrustacean hexapod invertebrates of the class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body ( head, thorax and abdomen), three pa ...

s, small

vertebrate Vertebrates () comprise all animal taxa within the subphylum Vertebrata () ( chordates with backbones), including all mammals, birds, reptiles, amphibians, and fish. Vertebrates represent the overwhelming majority of the phylum Chordata, with ...

s, and plant material.

Status as a chimera

Rauhut and Remes (2005) found ''Alwalkeria'' to be a chimera, with the anterior skull referable to a crurotarsan, and the vertebrae referable to various other ancient

reptile Reptiles, as most commonly defined are the animals in the class Reptilia ( ), a paraphyletic grouping comprising all sauropsids except birds. Living reptiles comprise turtles, crocodilians, squamates ( lizards and snakes) and rhynchocephalia ...

s including Prolacertiformes. The

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

. However Langer (2004) and Martínez and Alcober (2009), observed that ''Alwalkeria'' was too primitive to be a

theropod Theropoda (; ), whose members are known as theropods, is a dinosaur clade that is characterized by hollow bones and three toes and claws on each limb. Theropods are generally classed as a group of saurischian dinosaurs. They were ancestrally c ...

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 Cladistics (; ) is an approach to biological classification in which organisms are categorized in groups ("clades") based on hypotheses of most recent common ancestry. The evidence for hypothesized relationships is typically shared derived char ...

analysis, but its similarities to ''

'' 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 Theropoda (; ), whose members are known as theropods, is a dinosaur clade that is characterized by hollow bones and three toes and claws on each limb. Theropods are generally classed as a group of saurischian dinosaurs. They were ancestrally ...

- Sauropodomorpha split.

Paul Sereno Paul Callistus Sereno (born October 11, 1957) is a professor of paleontology at the University of Chicago and a National Geographic "explorer-in-residence" who has discovered several new dinosaur species on several continents, including at si ...

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 In phylogenetics, an autapomorphy is a distinctive feature, known as a derived trait, that is unique to a given taxon. That is, it is found only in one taxon, but not found in any others or outgroup taxa, not even those most closely related to ...

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: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 The spinal column, a defining synapomorphy shared by nearly all vertebrates,Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characteristic i ...

(debated because the vertebrae likely don't belong to ''Alwalkeria'') * the presence of a highly expanded

femoral head The femoral head (femur head or head of the femur) is the highest part of the thigh bone (femur). It is supported by the femoral neck. Structure The head is globular and forms rather more than a hemisphere, is directed upward, medialward, and a l ...

* the fourth trochanter is very prominent Several features would make ''Alwalkeria'' unique among basal dinosaurs, such as its lack of serrated teeth, the

mandibular symphysis In human anatomy, the facial skeleton of the skull the external surface of the mandible is marked in the median line by a faint ridge, indicating the mandibular symphysis (Latin: ''symphysis menti'') or line of junction where the two lateral halve ...

being proportionally wider than almost any other known dinosaur, and there is a very large articulation between the

fibula The fibula or calf bone is a leg bone on the lateral side of the tibia, to which it is connected above and below. It is the smaller of the two bones and, in proportion to its length, the most slender of all the long bones. Its upper extremity ...

and the

ankle The ankle, or the talocrural region, or the jumping bone (informal) is the area where the foot and the leg meet. The ankle includes three joints: the ankle joint proper or talocrural joint, the subtalar joint, and the inferior tibiofibular joi ...

Paleoecology

Provenance and occurrence

The only known specimen of ''Alwalkeria'' was recovered in the

Godavari The Godavari ( IAST: ''Godāvarī'' �od̪aːʋəɾiː is India's second longest river after the Ganga river and drains into the third largest basin in India, covering about 10% of India's total geographical area. Its source is in Trimbakesh ...

Valley locality from the Maleri Formation of

Andhra Pradesh Andhra Pradesh (, abbr. AP) is a state in the south-eastern coastal region of India. It is the seventh-largest state by area covering an area of and tenth-most populous state with 49,386,799 inhabitants. It is bordered by Telangana to the ...

. The remains were collected by S. Chatterjee in 1974 in red

mudstone Mudstone, a type of mudrock, is a fine-grained sedimentary rock whose original constituents were clays or muds. Mudstone is distinguished from '' shale'' by its lack of fissility (parallel layering).Blatt, H., and R.J. Tracy, 1996, ''Petrology.' ...

that was deposited during the

Carnian The Carnian (less commonly, Karnian) is the lowermost stage (stratigraphy), stage of the Upper Triassic series (stratigraphy), Series (or earliest age (geology), age of the Late Triassic Epoch (reference date), Epoch). It lasted from 237 to 227 m ...

stage of the

Triassic The Triassic ( ) is a geologic period and system which spans 50.6 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.36 Mya. The Triassic is the first and shortest per ...

period, approximately 235 to 228 million years ago. The specimen is housed in the collection of the

Indian Statistical Institute Indian Statistical Institute (ISI) is a higher education and research institute which is recognized as an Institute of National Importance by the 1959 act of the Indian parliament. It grew out of the Statistical Laboratory set up by Prasanta C ...

, in

Kolkata Kolkata (, or , ; also known as Calcutta , the official name until 2001) is the capital of the Indian state of West Bengal, on the eastern bank of the Hooghly River west of the border with Bangladesh. It is the primary business, comme ...

, 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 ''Nambalia'' is a genus of basal sauropodomorph dinosaur. It lived during the Late Triassic period (late Norian to earliest Rhaetian) in what is now Telangana, central India. It is known from the holotype ISI R273, parts 1–3, partially ...

'' 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.

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 Prehistoric saurischians Late Triassic dinosaurs of Asia Carnian genera Dinosaurs of India and Madagascar Fossils of India Fossil taxa described in 1994 Taxa named by Sankar Chatterjee