![Alwalkeria g](https://upload.wikimedia.org/wikipedia/commons/a/a0/Alwalkeria_g.png)
''Alwalkeria'' (; "for Alick Walker") is a
genus
Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...
partly based on
basal saurischia
Saurischia ( , meaning "reptile-hipped" from the Greek ' () meaning 'lizard' and ' () meaning 'hip joint') is one of the two basic divisions of dinosaurs (the other being Ornithischia), classified by their hip structure. Saurischia and Ornithis ...
n
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 (geology), epoch of the Triassic geologic time scale, Period in the geologic time scale, spanning the time between annum, Ma and Ma (million years ago). It is preceded by the Middle Triassic Epoch ...
, living in
India
India, officially the Republic of India (Hindi: ), is a country in South Asia. It is the seventh-largest country by area, the second-most populous country, and the most populous democracy in the world. Bounded by the Indian Ocean on the so ...
. 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
Chimera, Chimaera, or Chimaira (Greek for " she-goat") originally referred to:
* Chimera (mythology), a fire-breathing monster of Ancient Lycia said to combine parts from multiple animals
* Mount Chimaera, a fire-spewing region of Lycia or Cilicia ...
.
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 of ...
in 1987, in honor of
British
British may refer to:
Peoples, culture, and language
* British people, nationals or natives of the United Kingdom, British Overseas Territories, and Crown Dependencies.
** Britishness, the British identity and common culture
* British English, ...
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, Linn ...
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 l ...
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
![Alwalkeria maleriensis](https://upload.wikimedia.org/wikipedia/commons/0/06/Alwalkeria_maleriensis.jpg)
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 several ...
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 characteristic ...
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 with ...
, and an
astragalus
''Astragalus'' is a large genus of over 3,000 species of herbs and small shrubs, belonging to the legume family Fabaceae and the subfamily Faboideae. It is the largest genus of plants in terms of described species. The genus is native to tempe ...
(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, the ...
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 northwest ...
''. 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 b ...
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. The 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
Gregory Scott Paul (born December 24, 1954) is an American freelance researcher, author and illustrator who works in paleontology, and more recently has examined sociology and theology. He is best known for his work and research on theropod dino ...
estimated its weight at 2 kg and length at 1.5 m in 2010.
Dentition and diet
The holotype had
heterodont 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
Sauropodomorpha ( ; from Greek, meaning "lizard-footed forms") is an extinct clade of long-necked, herbivorous, saurischian dinosaurs that includes the sauropods and their ancestral relatives. Sauropods generally grew to very large sizes, had lon ...
, 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 th ...
y
theropods
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 ca ...
, 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 mouthpart ...
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 sof ...
, 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 nutr ...
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 pairs ...
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, ...
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
Crurotarsi is a clade of archosauriform reptiles that includes crocodilians and stem-crocodilians and possibly bird-line archosaurs too if the extinct, crocodile-like phytosaurs are more distantly related to crocodiles than traditionally thoug ...
, 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 rhynchocephalians ( ...
s including
Prolacertiformes
Protorosauria is an extinct polyphyletic group of archosauromorph reptiles from the latest Middle Permian (Capitanian stage) to the end of the Late Triassic (Rhaetian stage) of Asia, Europe and North America. It was named by the English anatomis ...
. The
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 with ...
and the
astragalus
''Astragalus'' is a large genus of over 3,000 species of herbs and small shrubs, belonging to the legume family Fabaceae and the subfamily Faboideae. It is the largest genus of plants in terms of described species. The genus is native to tempe ...
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
''Protoavis'' (meaning "first bird") is a problematic taxon known from fragmentary remains from Late Triassic Norian stage deposits near Post, Texas. Much controversy remains over the animal, and there are many different interpretations of what ...
'', and hence assigned it to
Herrerasauridae
Herrerasauridae is a family of carnivorous dinosaurs, possibly basal to either theropods or even all of saurischians, or even their own branching from dracohors, separate from dinosauria altogether. They are among the oldest known dinosaurs, ...
based on features of the
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 with ...
. 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
saurischia
Saurischia ( , meaning "reptile-hipped" from the Greek ' () meaning 'lizard' and ' () meaning 'hip joint') is one of the two basic divisions of dinosaurs (the other being Ornithischia), classified by their hip structure. Saurischia and Ornithis ...
n.
[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
Saurischia ( , meaning "reptile-hipped" from the Greek ' () meaning 'lizard' and ' () meaning 'hip joint') is one of the two basic divisions of dinosaurs (the other being Ornithischia), classified by their hip structure. Saurischia and Ornithis ...
.
''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 ''
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 northwest ...
'' 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
Saurischia ( , meaning "reptile-hipped" from the Greek ' () meaning 'lizard' and ' () meaning 'hip joint') is one of the two basic divisions of dinosaurs (the other being Ornithischia), classified by their hip structure. Saurischia and Ornithis ...
, 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 ca ...
-
Sauropodomorpha
Sauropodomorpha ( ; from Greek, meaning "lizard-footed forms") is an extinct clade of long-necked, herbivorous, saurischian dinosaurs that includes the sauropods and their ancestral relatives. Sauropods generally grew to very large sizes, had lon ...
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 sites ...
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 t ...
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 ...
(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
A trochanter is a tubercle of the femur near its joint with the hip bone. In humans and most mammals, the trochanters serve as important muscle attachment sites. Humans are known to have three trochanters, though the anatomic "normal" includes ...
is very prominent
Several features would make ''Alwalkeria'' unique among basal dinosaurs, such as its lack of
serrated
Serration is a saw-like appearance or a row of sharp or tooth-like projections. A serrated cutting edge has many small points of contact with the material being cut. By having less contact area than a smooth blade or other edge, the applied pr ...
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 halves ...
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 is ...
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 join ...
.
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 ...
,
India
India, officially the Republic of India (Hindi: ), is a country in South Asia. It is the seventh-largest country by area, the second-most populous country, and the most populous democracy in the world. Bounded by the Indian Ocean on the so ...
. 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 of the Upper Triassic Series (or earliest age of the Late Triassic Epoch). It lasted from 237 to 227 million years ago (Ma). The Carnian is preceded by the Ladinian and is followed by t ...
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 period ...
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
''Jaklapallisaurus'' is a genus of unaysaurid 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 R274, postcranial ...
'' 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 a ...
'' 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