Rajasaurus (lit. 'King lizard') is a genus of carnivorous abelisaurid theropod dinosaur from the Late Cretaceous of India, containing one species: Rajasaurus narmadensis. The bones were excavated from the Lameta Formation in the Gujarat state of Western India, probably inhabiting what is now the Narmada River Valley. It was formally described by palaeontologist Jeffrey A. Wilson and colleagues in 2003 based on a partial skeleton comprising the braincase, spine, hip bone, legs, and tail–a first for an Indian theropod. The dinosaur likely measured 6.6 metres (22 ft), and had a single horn on the forehead which was probably used for display and head-butting. Like other abelisaurids, Rajasaurus was probably an ambush predator. India at this time was an island, due to the break-up of the supercontinent Gondwana, though it is possible animals still were able to migrate to and from nearby continents. The creation of the subfamily Majungasaurinae, and its inclusion of abelisaurids from India, Madagascar, and Europe–including Rajasaurus–further reiterates this. The Lameta Formation has yielded several other dinosaur species, including abelisaurids and titanosaurian sauropods, similar to other Gondwanan landmasses. The area during the Cretaceous was probably forested, and served as nesting grounds for several creatures.
Discovery and naming
The Lameta Formation was first discovered in 1981 by geologists working for the Geological Survey of India (GSI), G. N. Dwivedi and Dhananjay Mahendrakumar Mohabey, after being given limestone structures–later recognised as dinosaur eggs–by workers of the ACC Cement Quarry in the village of Rahioli near the city Balasinor in the Gujarat state of western India. The remains of Rajasaurus were found in this fossil-rich limestone bed to which GSI geologist Suresh Srivastava was assigned to excavate on two separate trips from 1982–1983 and 1983–1984. In 2001, teams from the American Institute of Indian Studies and the National Geographic Society, with the support of the Panjab University, joined the study in order to reconstruct the excavated remains. Fragments of Rajasaurus were also found near Jabalpur in Madhya Pradesh in the northern part of the Lameta Formation, namely a piece of the upper jaw. Rajasaurus was then formally described in 2003 by geologist Jeffrey A. Wilson and colleagues. The holotype specimen of Rajasaurus comprises a partial skeleton, GSI Type No. 21141/1-33, which includes the maxillae, premaxillae, braincase, and quadrate bone on the skull; and spine, hip bone, legs, and tail in post-cranial remains. It is the first Indian theropod to have preserved these post-cranial remains. It is possible Rajasaurus, Lametasaurus, and Indosaurus are synonymous, though this cannot be confirmed due to fragmentary remains, and the Lametasaurus specimen has been lost. The generic name Rajasaurus derives from the Sanskrit rāja, meaning 'king, sovereign, chief, or best of its kind' and Ancient Greek sauros, meaning 'lizard'; and its specific name narmadensis refers to the Narmada River in central India near where it was discovered.
Description
In 2010, palaeontologist Gregory S. Paul estimated the body length of Rajasaurus at 11 metres (36 ft) and weight at 4 metric tons (4.4 short tons). In 2016, its length was estimated to be 6.6 metres (22 ft), with the known vertebrae significantly smaller in size than those of Pycnonemosaurus, Carnotaurus and Ekrixinatosaurus. Rajasaurus closely resembled the Madagascan abelisaurid Majungasaurus. Rajasaurus typically had four fingers, short arms, and, to compensate, a heavily-constructed head which was the primary tool for hunting; however, the skull was short, they probably had modest jaw musculature, and the teeth were short. Rajasaurus probably had a bite force similar to Allosaurus at around 3,500 newtons (790 lbf). The pelvis and hindlimb bones of the contemporaneous Lametasaurus have been suggested to belong to Rajasaurus, based on shared features in the ilium. It also appears to be from a larger specimen than the holotype.
Skull On the braincase, only the left sides of the parietal and frontal bones are preserved. The braincase is thick, with the frontals achieving a maximum thickness of 4 centimetres (1.6 in) above the eye socket. On the frontals near the midline is a path for the olfactory tract which is a part of smelling. The rims of the supratemporal fossae, depressions on either side of the top of the skull, form a low sagittal crest along the middle of the top of the skull. The front rims of the fossae are unusually steep. Abelisaurids, typically, had elongated fenestrae (holes in the skull) below the quadrate bone near the bottom of the skull, but Rajasaurus had elongated supratemporal fenestrae near the top of the skull. Unlike in other theropods but similar to Majungasaurus, the crista prootica, which is typically a ridge along the otic capsule bone in the ear, more so juts outward as a stump.
Rajasaurus had a low horn on its forehead that is primarily made of nasal bone more than frontal, unlike the horn on Majungasaurus. The horn in life was probably the same size as the fossilised horn, unlike in Carnotaurus where in life the horn was extended by a thickened layer skin. Though Rajasaurus, like Majungasaurus, did have a thickened layer of skin, it probably did not add to the overall length of the horn. A trough-like groove bordered by a raised wall is present where the frontal meets the nasal, decreasing in height and width towards the midline, serving to support the horn on the nasal.
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