| Rajasaurus | |
|---|---|
 | |
| Reconstructed skull,Regional Museum of Natural History, Bhopal | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Clade: | Dinosauria |
| Clade: | Saurischia |
| Clade: | Theropoda |
| Family: | †Abelisauridae |
| Subfamily: | †Majungasaurinae |
| Genus: | †Rajasaurus Wilson et al.,2003 |
| Species: | †R. narmadensis |
| Binomial name | |
| †Rajasaurus narmadensis Wilson et al., 2003 | |
Rajasaurus (/rɑːdʒə/lit. 'King lizard') is agenus of carnivorousabelisauridtheropod dinosaur from theLate Cretaceous of India, containing onespecies:Rajasaurus narmadensis. The bones were excavated from theLameta Formation in theGujarat state ofWestern India, probably inhabiting what is now theNarmada River Valley. It was formallydescribed bypalaeontologistJeffrey A. Wilson and colleagues in 2003 based on a partial skeleton comprising thebraincase,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 fordisplay and head-butting. Like other abelisaurids,Rajasaurus was probably anambush predator.
India at this time was an island, due to the break-up of thesupercontinentGondwana, though it is possible animals still were able to migrate to and from nearby continents. The creation of the subfamilyMajungasaurinae, and its inclusion of abelisaurids from India, Madagascar, and Europe–includingRajasaurus–further reiterates this. The Lameta Formation has yielded several other dinosaur species, including abelisaurids andtitanosauriansauropods, similar to other Gondwanan landmasses. The area during the Cretaceous was probably forested, and served as nesting grounds for several creatures.
TheLameta Formation was first discovered in 1981 bygeologists working for theGeological Survey of India (GSI), G. N. Dwivedi and Dhananjay Mahendrakumar Mohabey, after being givenlimestone structures–later recognised asdinosaur eggs–by workers of the ACC Cement Quarry in the village of Rahioli near the cityBalasinor in theGujarat state ofwestern India. The remains ofRajasaurus 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 theAmerican Institute of Indian Studies and theNational Geographic Society, with the support of thePanjab University, joined the study in order to reconstruct the excavated remains. Fragments ofRajasaurus were also found nearJabalpur inMadhya Pradesh in the northern part of the Lameta Formation, namely a piece of the upper jaw.[1]Rajasaurus was then formallydescribed in 2003 by geologistJeffrey A. Wilson and colleagues.[2]
Theholotype specimen ofRajasaurus comprises a partial skeleton, GSI Type No. 21141/1-33, which includes themaxillae,premaxillae,braincase, andquadrate bone on the skull; andspine, hip bone, legs, and tail inpost-cranial remains. It is the first Indiantheropod to have preserved these post-cranial remains. It is possibleRajasaurus,Lametasaurus, andIndosaurus aresynonymous, though this cannot be confirmed due to fragmentary remains, and theLametasaurus specimen has been lost.[2][3]
Thegeneric nameRajasaurus derives from theSanskritrāja, meaning 'king, sovereign, chief, or best of its kind' andAncient Greeksauros, meaning 'lizard'; and itsspecific namenarmadensis refers to theNarmada River in central India near where it was discovered.[2]
In 2010, palaeontologistGregory S. Paul estimated the body length ofRajasaurus at 11 metres (36 ft) and weight at 4 metric tons (4.4 short tons).[4] In 2016, its length was estimated to be 6.6 metres (22 ft), with the known vertebrae significantly smaller in size than those ofPycnonemosaurus,Carnotaurus andEkrixinatosaurus.[5]Rajasaurus closely resembled the Madagascan abelisauridMajungasaurus.[6]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.[4]Rajasaurus probably had a bite force similar toAllosaurus at around 3,500 newtons (790 lbf).[7] The pelvis and hindlimb bones of the contemporaneousLametasaurus have been suggested to belong toRajasaurus, based on shared features in theilium.[8] It also appears to be from a larger specimen than the holotype.[9]
On the braincase, only the left sides of theparietal andfrontal bones are preserved. The braincase is thick, with the frontals achieving a maximum thickness of 4 centimetres (1.6 in) above theeye socket. On the frontals near the midline is a path for theolfactory tract which is a part of smelling. The rims of thesupratemporal fossae, depressions on either side of the top of the skull, form a lowsagittal crest along the middle of the top of the skull. The front rims of the fossae are unusually steep. Abelisaurids, typically, had elongatedfenestrae (holes in the skull) below thequadrate bone near the bottom of the skull, butRajasaurus had elongatedsupratemporal fenestrae near the top of the skull. Unlike in other theropods but similar toMajungasaurus, the crista prootica, which is typically a ridge along theotic capsule bone in the ear, more so juts outward as a stump.[2]
Rajasaurus had a low horn on its forehead that is primarily made ofnasal bone more than frontal, unlike the horn onMajungasaurus. The horn in life was probably the same size as the fossilised horn, unlike inCarnotaurus where in life the horn was extended by a thickened layer skin. ThoughRajasaurus, likeMajungasaurus, did have a thickened layer of skin, it probably did not add to the overall length of the horn.[7] 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.[2]
Only oneneck 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 twoair pockets, though they are unusually close to the head. Eleven partial spool-shapeddorsal 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 sixsacral vertebrae are preserved; they are elongated and have a decreasing width towards the ends, and have no arching. Three partialtail vertebrae were found, likely from the middle-section of the tail, and they also have concave faces, but are more cylindrical than spool-shaped.[2][10]
The part of the hip that juts out to attach to theischium, the ischial peduncle, projects farther out than thepubic peduncle, which causes thehip-joint to be farther down on the back-underside of the hip. Theiliac crests, on the other side of the hip from the ischium and pubic bone, are thin compared to the hip-joint area, 1 and 8 centimetres (0.39 and 3.15 in) respectively in thickness. Thefibula, on the outside portion of the lower leg below the knee, decreases in width from top to bottom and is slightly concave. Similar toCeratosaurus, thesecond metatarsal bone which connects theankle 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. Thefourth metatarsal bone has similar proportions to the second metatarsal. Both second metatarsals are preserved and only the left fourth metatarsal is preserved.[2]
Wilson, in 2003, assignedRajasaurus to the subfamilyCarnotaurinae, being more closely related to abelisaurids likeMajungasaurus and the South AmericanCarnotaurus 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 thickskull roof.[2] However, if this were the case, then African abelisaurids would display endemism and notRajasaurus.[11] In 2008, palaeontologist Matthew Carrano created the subfamilyBrachyrostra for South American abelisaurids as asister 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 theMiddle Cretaceous.[3][12][13]
In 2014, the subfamilyMajungasaurinae was erected by palaeontologist Thierry Tortosa to separate the newly discovered EuropeanArcovenator,Majungasaurus,Indosaurus,Rahiolisaurus, andRajasaurus from South American abelisaurids based on physical characteristics such as elongatedantorbital 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 allowedisland hopping and an indirect path to Asia, though these are still questionable explanations.[14][15]
The following cladogram was recovered by Tortosa (2014):[14]
Rajasaurus is distinguished from other genera by its single forehead horn (thoughMajungasaurus also only has one), the elongatedsupratemporal fenestrae (holes in the upper rear of the skull), and theilia bones on the hip which feature a ridge separating thebrevis shelf from the hip joint.[2]
The horn ofRajasaurus could have been used fordisplay or head-butting with otherRajasaurus individuals.[4] Head-butting, inferred from the lack of shock-absorbingcancellous bone in the skull, could have been both or either low-motion shoving matches like modern daymarine iguanas (Amblyrhynchus cristatus), or focused on the neck and the flank likegiraffes (Giraffa spp.). The neck muscles, though, in abelisaurids were adapted for withstanding highstress. The horn could have been used for defendingterritory or for mating matches.[7]
Abelisaurids may have beenambush predators, using a bite-and-hold tactic to hunt large prey. The leg bones ofMajungasaurus are comparatively short to other similarly-sized theropods, suggesting the dinosaur was comparatively slower–this same condition is seen inRajasaurus. However, ceratosaurs may have been able to rapidly accelerate.[7][16]
Rajasaurus has been found in the Lameta Formation, a rock unitradiometrically dated to theMaastrichtianage of the latest Cretaceous representing anarid orsemi-arid landscape with a river flowing through it–probably providing shrub cover near the water–which formed between episodes of volcanism in theDeccan Traps.[2][1][17][18]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;[19] though eggs belonging to large theropods have been found, it is unknown if they belong toRajasaurus.[20] Sauropodcoprolite remains indicate they lived in a forested landscape, consuming plants such asPodocarpus,Araucaria, andCheirolepidiaceaeconifers;cycads;palm trees; earlygrass; andCaryophyllaceae,Sapindaceae, andAcanthaceae flowering plants.[21]Ferns were also common in India withOsmundaceae,Schizaeales,Dicksoniaceae,Gleicheniaceae andSalviniales being found.[22] The prehistoric snakeSanajeh mainly raided the nests of sauropods for eggs, though it is possible it also targeted smaller theropod eggs.[23]
India, by the Late Cretaceous, had separated from Madagascar and South America during the break-up of Gondwana, andRajasaurus lived on an isolated island, likely causingendemism and unique characteristics not seen in other abelisaurids.[1][24] 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.[contradictory][25] The similarity between European and Indian sauropodegg taxa suggests an inter-continental migration of animals between India, Europe, and South America during the Cretaceous, despite water barriers.[26]
Several dinosaurs have been described from the Lameta Formation, such as thenoasauridLaevisuchus; abelisauridsIndosaurus,Indosuchus,Lametasaurus, andRahiolisaurus; and thetitanosaurian sauropodsJainosaurus,Titanosaurus, andIsisaurus. 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.[2][27]
The dinosaurs in India probably all went extinct due to volcanic activity around 350,000 years before theCretaceous–Paleogene boundary. Dinosaurs probably avoided areas with volcanicfissure vents andlava flows.[relevant?][28]
The Gujarat state has declared the fossil site in Balasinor a "dinosaur park," sometimes called the "Jurassic Park of India" in reference to the1993 film, in response to the massive rush of tourism, with the crowning attraction beingRajasaurus.[29] In Rahioli, a life-sized statue was erected in honour of its discovery.[30] The Indiantheme parkAdlabs Imagica features the Rajasaurus River Adventure, a water ride following the fictional "Dr. Roy" through prehistoric times.[31]Rajasaurus also appeared in the "Badlands" episode ofPrehistoric Planet, where at least two individuals are shown hunting downIsisaurus hatchlings as they pass through the volcanic fields of theDeccan Traps.
Media related toRajasaurus at Wikimedia Commons
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