Alwalkeria
Encyclopedia
Alwalkeria is a genus
of basal
saurischia
n dinosaur
from the Late Triassic
of India
. It was a small bipedal omnivore
.
This dinosaur was originally named Walkeria maleriensis by Sankar Chatterjee
in 1987, in honor of famous British
paleontologist Alick Walker
and the Maleri Formation, in which its fossil
s were found. However, the original generic name was found to be preoccupied
by a bryozoa
n. A new name was created in 1994 by Chatterjee and Ben Creisler.
Remains of Alwalkeria have been recovered from the Maleri Formation of Andhra Pradesh
, India
. This is a Late Triassic geologic formation
. Indeterminate prosauropod material has also been found in the Maleri, but Alwalkeria is the only named dinosaur species. The one known specimen is partial 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
(thigh bone), 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 premaxilla
ry and the maxilla
ry bones of the upper jaw. Other similarities in the skull of the two animals also link them on morphologic
grounds (Langer 2004).
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. One recent analysis finds it within the order Saurischia
, but basal to the Theropoda
-Sauropodomorpha
split (Langer 2004). Paul Sereno
finds instead that Eoraptor is a basal theropod (Sereno 1999). Others place Eoraptor outside of Dinosauria completely (Fraser et al. 2002).
This dinosaur also has a heterodont dentition
in the upper jaw, meaning that the teeth are differently shaped depending on their position within 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 are serrated. This arrangement of teeth is neither clearly herbviorous
nor clearly carnivorous
, which suggests that this dinosaur was an omnivore with a varied diet, including insect
s, small vertebrate
s, and plant material.
Several features make Alwalkeria unique among basal dinosaurs. Besides its unserrated teeth, and the mandibular symphysis
is proportionally wider than almost any other known dinosaur. Also, there is a very large articulation between the fibula and the ankle.
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
of basal
Basal (phylogenetics)
In phylogenetics, a basal clade is the earliest clade to branch in a larger clade; it appears at the base of a cladogram.A basal group forms an outgroup to the rest of the clade, such as in the following example:...
saurischia
Saurischia
Saurischia meaning 'lizard' and ischion meaning 'hip joint') is one of the two orders, or basic divisions, of dinosaurs. In 1888, Harry Seeley classified dinosaurs into two orders, based on their hip structure...
n dinosaur
Dinosaur
Dinosaurs are a diverse group of animals of the clade and superorder Dinosauria. They were the dominant terrestrial vertebrates for over 160 million years, from the late Triassic period until the end of the Cretaceous , when the Cretaceous–Paleogene extinction event led to the extinction of...
from the Late Triassic
Late Triassic
The Late Triassic is in the geologic timescale the third and final of three epochs of the Triassic period. The corresponding series is known as the Upper Triassic. In the past it was sometimes called the Keuper, after a German lithostratigraphic group that has a roughly corresponding age...
of India
India
India , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world...
. It was a small bipedal omnivore
Omnivore
Omnivores are species that eat both plants and animals as their primary food source...
.
This dinosaur was originally named Walkeria maleriensis by Sankar Chatterjee
Sankar Chatterjee
Sankar Chatterjee 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 Calcutta in 1970 and was a Post-doctoral Fellow at the Smithsonian...
in 1987, in honor of famous British
United Kingdom
The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...
paleontologist Alick Walker
Alick Walker
Alick Donald Walker was a British palaeontologist, after whom the Alwalkeria genus of dinosaur is named....
and the Maleri Formation, in which its fossil
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...
s were found. However, the original generic name was found to be preoccupied
International Code of Zoological Nomenclature
The International Code of Zoological Nomenclature is a widely accepted convention in zoology that rules the formal scientific naming of organisms treated as animals...
by a bryozoa
Bryozoa
The Bryozoa, also known as Ectoprocta or commonly as moss animals, are a phylum of aquatic invertebrate animals. Typically about long, they are filter feeders that sieve food particles out of the water using a retractable lophophore, a "crown" of tentacles lined with cilia...
n. A new name was created in 1994 by Chatterjee and Ben Creisler.
Remains of Alwalkeria have been recovered from the Maleri Formation of Andhra Pradesh
Andhra Pradesh
Andhra Pradesh , is one of the 28 states of India, situated on the southeastern coast of India. It is India's fourth largest state by area and fifth largest by population. Its capital and largest city by population is Hyderabad.The total GDP of Andhra Pradesh is $100 billion and is ranked third...
, India
India
India , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world...
. This is a Late Triassic geologic formation
Geologic formation
A formation or geological formation is the fundamental unit of lithostratigraphy. A formation consists of a certain number of rock strata that have a comparable lithology, facies or other similar properties...
. Indeterminate prosauropod material has also been found in the Maleri, but Alwalkeria is the only named dinosaur species. The one known specimen is partial 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
Femur
The femur , or thigh bone, is the most proximal bone of the leg in tetrapod vertebrates capable of walking or jumping, such as most land mammals, birds, many reptiles such as lizards, and amphibians such as frogs. In vertebrates with four legs such as dogs and horses, the femur is found only in...
(thigh bone), and an astragalus
Talus bone
-External links:* *...
(ankle bone). The partial skull
Skull
The skull is a bony structure in the head of many animals that supports the structures of the face and forms a cavity for the brain.The skull is composed of two parts: the cranium and the mandible. A skull without a mandible is only a cranium. Animals that have skulls are called craniates...
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 premaxilla
Premaxilla
The incisive bone is the portion of the maxilla adjacent to the incisors. It is a pair of small cranial bones at the very tip of the jaws of many animals, usually bearing teeth, but not always. They are connected to the maxilla and the nasals....
ry and the maxilla
Maxilla
The maxilla is a fusion of two bones along the palatal fissure that form the upper jaw. This is similar to the mandible , which is also a fusion of two halves at the mental symphysis. Sometimes The maxilla (plural: maxillae) is a fusion of two bones along the palatal fissure that form the upper...
ry bones of the upper jaw. Other similarities in the skull of the two animals also link them on morphologic
Morphology (biology)
In biology, morphology is a branch of bioscience dealing with the study of the form and structure of organisms and their specific structural features....
grounds (Langer 2004).
Alwalkeria has not been included in a cladistic analysis, but its similarities to Eoraptor
Eoraptor
Eoraptor was one of the world's earliest dinosaurs. It was a two-legged saurischian, close to the ancestry of theropods and sauropodomorphs. It lived ca. 231.4 million years ago, in what is now the northwestern region of Argentina...
suggest it may have held a similar position in the dinosaur family tree. However, the position of Eoraptor is disputed. One recent analysis finds it within the order Saurischia
Saurischia
Saurischia meaning 'lizard' and ischion meaning 'hip joint') is one of the two orders, or basic divisions, of dinosaurs. In 1888, Harry Seeley classified dinosaurs into two orders, based on their hip structure...
, but basal to the Theropoda
Theropoda
Theropoda is both a suborder of bipedal saurischian dinosaurs, and a clade consisting of that suborder and its descendants . Dinosaurs belonging to the suborder theropoda were primarily carnivorous, although a number of theropod groups evolved herbivory, omnivory, and insectivory...
-Sauropodomorpha
Sauropodomorpha
Sauropodomorpha is an extinct clade of long-necked, herbivorous, saurischian dinosaurs which includes the sauropods and their ancestral relatives. Sauropods generally grew to very large sizes, had long necks and tails, were quadrupedal, and became the largest animals to ever walk the Earth. The...
split (Langer 2004). Paul Sereno
Paul Sereno
Paul Callistus Sereno is an American paleontologist from the University of Chicago who discovered several new dinosaur species on several continents. He has conducted excavations at sites as varied as Inner Mongolia, Argentina, Morocco, and Niger...
finds instead that Eoraptor is a basal theropod (Sereno 1999). Others place Eoraptor outside of Dinosauria completely (Fraser et al. 2002).
This dinosaur also has a heterodont dentition
Dentition
Dentition pertains to the development of teeth and their arrangement in the mouth. In particular, the characteristic arrangement, kind, and number of teeth in a given species at a given age...
in the upper jaw, meaning that the teeth are differently shaped depending on their position within 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 are serrated. This arrangement of teeth is neither clearly herbviorous
Herbivore
Herbivores are organisms that are anatomically and physiologically adapted to eat plant-based foods. Herbivory is a form of consumption in which an organism principally eats autotrophs such as plants, algae and photosynthesizing bacteria. More generally, organisms that feed on autotrophs in...
nor clearly carnivorous
Carnivore
A carnivore meaning 'meat eater' is an organism that derives its energy and nutrient requirements from a diet consisting mainly or exclusively of animal tissue, whether through predation or scavenging...
, which suggests that this dinosaur was an omnivore with a varied diet, including insect
Insect
Insects are a class of living creatures within the arthropods that have a chitinous exoskeleton, a three-part body , three pairs of jointed legs, compound eyes, and two antennae...
s, small vertebrate
Vertebrate
Vertebrates are animals that are members of the subphylum Vertebrata . Vertebrates are the largest group of chordates, with currently about 58,000 species described. Vertebrates include the jawless fishes, bony fishes, sharks and rays, amphibians, reptiles, mammals, and birds...
s, and plant material.
Several features make Alwalkeria unique among basal dinosaurs. Besides its unserrated teeth, and the mandibular symphysis
Mandible
The mandible pronunciation or inferior maxillary bone forms the lower jaw and holds the lower teeth in place...
is proportionally wider than almost any other known dinosaur. Also, there is a very large articulation between the fibula and the ankle.
External links
- Alwalkeria at Dinodata (text copied from The Dinosauria, First Edition, as Walkeria)
- Alwalkeria at Dinosaurier-Web (including Picture, in German)