Rajasaurus (‘Raja’ meaning “king” (derived from Sanskrit) here,”king of lizards”) is a genus of carnivorous abelisaurian theropod dinosaur with an unusual head crest. Between 1982 and 1984, its fossilized bones were discovered by Suresh Srivastava of the Geological Survey of India (GSI). Excavated from the Narmada River valley in Rahioli in the Mahisagar district of Gujarat, India, the find was announced as a new genus of dinosaur by American and Indian scientists on August 13, 2003.
Paleontologists Paul Sereno of the University of Chicago, Jeff Wilson of the University of Michigan, and Srivastava worked together as an Indo–American group to study the Narmada River fossils. The fossils represented the partial skeleton of the new species Rajasaurus narmadensis, which means “princely lizard from the Narmada Valley.” The fossilized bones of Rajasaurus have also been found in the upriver region of the Narmada, at Jabalpur, in the state of Madhya Pradesh.
Rajasaurus was an abelisaurid, a member of a group of theropod predators known to have lived only on landmasses that were part of the supercontinent Gondwana, such as Africa, India, Madagascar, and South America. Rajasaurus closely resembles Majungasaurus, a contemporary abelisaur from Madagascar, an island that had separated from the Indian landmass about 20 million years earlier. It was found to be an abelisaurid through a phylogenetic analysis of anatomical characteristics, and was described as a carnotaurine abelisaurid (the subfamily including Carnotaurus) because of the configuration of its nasal bones and its possession of a growth (“excrescence”) on its frontal bone. Rajasaurus is distinguished from other genera by its single nasal-frontal horn, the elongated proportions of its supratemporal fenestrae (holes in the upper rear of the skull), and the form of the ilia (principle bones of the hip) which feature a transverse ridge separating the brevis shelf from the hip joint.
Rajasaurus was identified from a partial skeleton including a part of the skull (braincase), backbone, hip bones, parts of the hind legs and tail. This specimen, GSI 21141/1–33, serves as the type specimen of the genus and species. In 2010, Gregory S. Paul estimated its body length at eleven metres, its weight at four tonnes. In 2016, its length was estimated to be 6.6 metres (21.7 ft) in a comprehensive analysis of abelisaur size. What is preserved of the skull shows it bore a distinctive low rounded horn, made up of outgrowths from the nasal and frontal bones.
The discovery of Rajasaurus could lead to additional information on the evolutionary relationships of abelisaurs, since previously described specimens from India were mainly isolated bones. At a press conference held in 2003 on the discovery of Rajasaurus, Sereno stated:
The discovery, which will be put for examination before global experts, was important since it would help in adding to the current knowledge of dinosaur belonging to the family of Abelisaur predators and adding a new angle to dinosaurs in the Indian subcontinent.
Rajasaurus has been found in the Lameta Formation. This rock unit represents a forested setting of rivers and lakes that formed between episodes of volcanism. The volcanic rocks are now known as the Deccan Traps. Rajasaur and sauropod fossils are known from river and lake deposits that were quickly buried by Deccan volcanic flows. Other dinosaurs from the Lameta Formation include the noasaurid Laevisuchus, abelisaurids Indosaurus and Indosuchus, and the titanosaurian sauropods Jainosaurus, Titanosaurus, and Isisaurus.
Coprolites have been recorded in the Lameta Formation, and the presence of fungi in coprolites indicates that leaves were eaten by the dinosaurs which lived in a tropical or subtropical climate. Another scientific study of similarities in egg taxa suggested close phyletic relationships that supports the existence of a terrestrial connection between dinosaurian fauna in India and Europe during the Cretaceous, and between two Gondwanan areas, Patagonia and India.