Rajasaurus

''Rajasaurus'' (meaning "princely 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 , 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 recognized 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 and weight at . In 2016, its length was estimated to be . ''Rajasaurus'' closely resembled the Madagascan abelisaurid '' Majungasaurus'', with a 20 million year separation. Abelisaurids 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. Abelisaurids probably had a bite force similar to ''Allosaurus'' at around .

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 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 fossilized horn, unlike in ''Carnotaurus'' where in life the horn was extended by a thickened layer skin. Though ''Rajasaurus'' 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.

Only one neck vertebra–likely a middle vertebra–is preserved, and it is proportionally shorter than that of other ceratosaurs, broader than is tall, and spool-shaped. Like in other ceratosaurs, the back face of the vertebra where it connects to another vertebra is very concave; however, unlike in other ceratosaurs, the front face is also concave. Like other ceratosaurs, the neck vertebra has two air pockets, though they are unusually close to the head. Eleven partial spool-shaped dorsal vertebrae were found, but only one–most likely the fourth thoracic vertebra–is well preserved; the faces are concave, and more deeper than broad, in contrast to the neck vertebra which is the opposite. These vertebrae contain many air pockets. The bottom-side of six sacral vertebrae are preserved; they are elongated and have a decreasing width towards the ends, and have no arching. Three partial tail vertebrae were found, likely from the middle-section of the tail, and they also have concave faces, but are more cylindrical than spool-shaped.

The part of the hip that juts out to attach to the ischium, the ischial peduncle, projects farther out than the pubic peduncle, which causes the hip-joint to be farther down on the back-underside of the hip. The iliac crests, on the other side of the hip from the ischium and pubic bone, are thin compared to the hip-joint area, respectively in thickness. The fibula, on the outside portion of the lower leg below the knee, decreases in width from top to bottom and is slightly concave. Similar to ''Ceratosaurus'', the second metatarsal bone which connects the ankle bone to the second toe, is robust, has an oval-shaped and slightly concave joint between it and the ankle, and the width does not decrease as it gets nearer the toes. The fourth metatarsal bone has similar proportions to the second metatarsal. Both second metatarsals are preserved and only the left fourth metatarsal is preserved.

Classification

Wilson, in 2003, assigned ''Rajasaurus'' to the subfamily Carnotaurinae, being more closely related to abelisaurids like ''Majungasaurus'' and the South American ''Carnotaurus'' than to African abelisaurids–as Africa, he believed, had separated from Gondwana first, and South America, India, and Madagascar were connected via Antarctica–on the basis of several similarities such as the presence of a sagittal crest, neck vertebrae with two air pockets, the configuration of the nasal bones, a fleshy growth (" excrescence") on the frontal bone, and a thick skull roof. However, if this were the case, then African abelisaurids would display endemism and not ''Rajasaurus''. In 2008, palaeontologist Matthew Carrano created the subfamily Brachyrostra for South American abelisaurids as a sister taxon to Carnotaurinae, with the abelisaurids migrating through the Gondwanan continents via small land connections as they broke apart until they were completely separated in the Middle Cretaceous.

In 2014, the subfamily Majungasaurinae was erected by palaeontologist Thierry Tortosa to separate the newly discovered European ''Arcovenator'', ''Majungasaurus'', ''Indosaurus'', ''Rahiolisaurus'', and ''Rajasaurus'' from South American abelisaurids based on physical characteristics such as elongated antorbital fenestrae in front of the eye sockets, and a sagittal crest that widens into a triangular surface towards the front of the head. Despite large oceanic barriers, it has been suggested that a migration of abelisaurids took place in the Late Cretaceous between Africa, Europe, Madagascar, and India which ultimately isolated South American abelisaurids; it is possible that migration occurred between Europe and India across Africa given its proximity to both, and the volcanic Dras-Kohistan island arc may have allowed island hopping and an indirect path to Asia, though these are still questionable explanations.

The following cladogram was recovered by Tortosa (2014):

''Rajasaurus'' is distinguished from other genera by its single forehead horn (though ''Majungasaurus'' also only has one), the elongated supratemporal fenestrae (holes in the upper rear of the skull), and the ilia bones on the hip which feature a ridge separating the brevis shelf from the hip joint.

Palaeobiology

The horn of ''Rajasaurus'' could have been used for display or head-butting with other ''Rajasaurus'' individuals. Head-butting, inferred from the lack of shock-absorbing cancellous bone in the skull, could have been both or either low-motion shoving matches like modern day marine iguanas (''Amblyrhynchus cristatus''), or focused on the neck and the flank like giraffes (''Giraffa'' spp.). The neck muscles, though, in abelisaurids were adapted for withstanding high stress. The horn could have been used for defending territory or for mating matches.

Abelisaurids may have been ambush predators, using a bite-and-hold tactic to hunt large prey. The leg bones of ''Majungasaurus'' are comparatively short to other similarly-sized theropods, suggesting the dinosaur was comparatively slower–this same condition is seen in ''Rajasaurus''. However, ceratosaurs may have been able to rapidly accelerate.

Palaeoecology

''Rajasaurus'' has been found in the Lameta Formation, a rock unit radiometrically dated to the Maastrichtian age of the latest Cretaceous representing an arid or semi-arid landscape with a river flowing through it–probably providing shrub cover near the water–which formed between episodes of volcanism in the Deccan Traps. ''Rajasaurus'' likely inhabited what is now the Narmada River Valley. The formation is known for being a sauropod nesting site, yielding several dinosaur eggs, and sauropod herds likely chose sandy soil for nesting; though eggs belonging to large theropods have been found, it is unknown if they belong to ''Rajasaurus''. Sauropod coprolite remains indicate they lived in a forested landscape, consuming plants such as Podocarpus, Araucaria, and Cheirolepidiaceae conifers; cycads; palm trees; early grass; and Caryophyllaceae, Sapindaceae, and Acanthaceae flowering plants. The prehistoric snake ''Sanajeh'' mainly raided the nests of sauropods for eggs, though it is possible it also targeted smaller theropod eggs.

India, by the Late Cretaceous, had separated from Madagascar and South America during the break-up of Gondwana, and ''Rajasaurus'' lived on an isolated island, likely causing endemism and unique characteristics not seen in other abelisaurids. However, despite being an island, there is no evidence of endemic animals with unique traits from Late Cretaceous India, perhaps indicating a continued connection to other parts of the world, likely Africa due to its proximity. The similarity between European and Indian sauropod egg taxa suggests an inter-continental migration of animals between India, Europe, and South America during the Cretaceous, despite water barriers.

Several dinosaurs have been described from the Lameta Formation, such as the noasaurid '' Laevisuchus''; abelisaurids ''Indosaurus'', '' Indosuchus'', ''Lametasaurus'', and ''Rahiolisaurus''; and the titanosaurian sauropods '' Jainosaurus'', '' Titanosaurus'', and ''Isisaurus''. The diversity of abelisauroid and titanosaurian dinosaurs in Cretaceous India indicates they shared close affinities to the dinosaur life of the other Gondwanan continents, which had similar inhabitants.

The dinosaurs in India probably all went extinct due to volcanic activity around 350,000 years before the Cretaceous–Paleogene boundary. Dinosaurs probably avoided areas with volcanic fissure vents and lava flows.

Cultural significance

The Gujarat state has declared the fossil site in Balasinor a "dinosaur park," sometimes called the "Jurassic Park of India" in reference to the 1993 film, in response to the massive rush of tourism, with the crowning attraction being ''Rajasaurus''. In Rahioli, a life-sized statue was erected in honour of its discovery. The Indian theme park Adlabs Imagica features the Rajasaurus River Adventure, a water ride following the fictional "Dr. Roy" through prehistoric times.

See also

* Timeline of ceratosaur research
* ''Dryptosauroides''
* '' Compsosuchus''
* '' Jubbulpuria''
* '' Ornithomimoides''
* '' Orthogoniosaurus''

References

External links

"''Rajasaurus'' stalked the banks of Narmada"
''The Hindu'', 2003
*

{{Portal bar, Dinosaurs, Cretaceous, India

Majungasaurines
Late Cretaceous dinosaurs
Dinosaurs of India and Madagascar
Fossil taxa described in 2003
Taxa named by Paul Sereno