Alwalkeria (meaning "for Alick Walker") is a genus of basal saurischian dinosaur from the Late Triassic of India. It was a small bipedal omnivore. It was about 1.6 feet (50 centimeters) long and weighed about as much as a turkey.
Alwalkeria size comparison
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 fossils were found. However, the original generic name was found to be preoccupied by a bryozoan. 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 premaxillary and the maxillary 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 insects, small vertebrates, 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.
Etymology[]
This dinosaur was originally named Walkeria maleriensis by Sankar Chatterjee in 1987, in honor of famous British paleontologist Alick Walker. However, the original generic name was found to be preoccupied by a bryozoan, a new name was created in 1994 by Chatterjee and Ben Creisler, Alwalkeria. The species name maleriensis is a reference to the Maleri Formation, in India, where its fossils were found.
Description[]
Life restoration
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.[1] Estimates suggest that Alwalkeria was at best 50 cm (1.6 ft) long.
Dentition and diet[]
This dinosaur also has a 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 chimaera, 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, or at least its hindlimb, 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:
- an excavation is present in the bases of the dorsal neural arches (debated because the vertebrae likely don't belong to Alwalkeria)
- the presence of a highly expanded femoral head
- 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 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.
JPInstitute.com Description[]
Alwalkeria was a small meat-eater and among the first dinosaurs on the Earth. Discovered in India, it may have been one of the first dinosaurs to live in that part of the world. These little hunters competed with other creatures, such as the mammal-like reptiles, for food. It would be many millions of years after this little dinosaur lived before dinosaurs ruled the Earth.
Known only from a few bones, it is believed that this specimen was a juvenile. It seems to be a standard form for the basal dinosaurs.