India at this time was an island, due to the break-up of the supercontinentGondwana, 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 titanosauriansauropods, 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 Narmada River, near which the remains of Rajasaurus were found
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.[1]Rajasaurus was then formally described in 2003 by geologist Jeffrey A. Wilson and colleagues.[2]
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.[2][3]
The generic nameRajasaurus derives from the Sanskritrāja, meaning 'king, sovereign, chief, or best of its kind' and Ancient Greeksauros, meaning 'lizard'; and its specific namenarmadensis refers to the Narmada River in central India near where it was discovered.[2]
Description
Scale diagram of Rajasaurus and a human
In 2010, palaeontologist Gregory S. Paul estimated the body length of Rajasaurus at 11 metres (36ft) and weight at 4 metric tons (4.4 short tons).[4] In 2016, its length was estimated to be 6.6 metres (22ft), with the known vertebrae significantly smaller in size than those of Pycnonemosaurus, Carnotaurus and Ekrixinatosaurus.[5]Rajasaurus closely resembled the Madagascan abelisaurid Majungasaurus.[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 to Allosaurus at around 3,500 newtons (790lbf).[7] The pelvis and hindlimb bones of the contemporaneous Lametasaurus have been suggested to belong to Rajasaurus, based on shared features in the ilium .[8] It also appears to be from a larger specimen than the holotype.[9]
Life restoration
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 (1.6in) 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.[2]
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 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 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.[2][10]
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, 1 and 8 centimetres (0.39 and 3.15in) 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.[2]
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.[2] However, if this were the case, then African abelisaurids would display endemism and not Rajasaurus.[11] 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.[3][12][13]
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.[14][15]
The following cladogram was recovered by Tortosa (2014):[14]
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.[2]
Palaeobiology
Restoration of Rajasaurus with prey
The horn of Rajasaurus could have been used for display or head-butting with other Rajasaurus individuals.[4] 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.[7]
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.[7][16]
Rajasaurus has been found in the Lameta Formation, a rock unit radiometrically dated to the Maastrichtianage 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.[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 to Rajasaurus.[20] Sauropod coprolite remains indicate they lived in a forested landscape, consuming plants such as Podocarpus, Araucaria, and Cheirolepidiaceaeconifers; cycads; palm trees; early grass; and Caryophyllaceae, Sapindaceae, and Acanthaceae flowering plants.[21] The prehistoric snake Sanajeh mainly raided the nests of sauropods for eggs, though it is possible it also targeted smaller theropod eggs.[22]
Rajasaurus and other dinosaurs would have faced intense volcanism due to the Deccan Traps
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.[1][23] 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][24] 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.[25]
Several dinosaurs have been described from the Lameta Formation, such as the noasauridLaevisuchus; 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.[2][26]
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.[28] In Rahioli, a life-sized statue was erected in honour of its discovery.[29] The Indian theme parkAdlabs Imagica features the Rajasaurus River Adventure, a water ride following the fictional "Dr. Roy" through prehistoric times.[30]Rajasaurus also appeared in the "Badlands" episode of Prehistoric Planet, where at least two individuals are shown hunting down Isisaurus hatchlings as they pass through the volcanic fields of the Deccan Traps.
Rapetosaurus is a genus of titanosaurian sauropod dinosaur that lived in Madagascar from 70 to 66 million years ago, at the end of the Cretaceous Period. Only one species, Rapetosaurus krausei, has been identified.
Carnotaurus is a genus of theropod dinosaur that lived in South America during the Late Cretaceous period, probably sometime between 71 and 69 million years ago. The only species is Carnotaurus sastrei. Known from a single well-preserved skeleton, it is one of the best-understood theropods from the Southern Hemisphere. The skeleton, found in 1984, was uncovered in the Chubut Province of Argentina from rocks of the La Colonia Formation. Carnotaurus is a derived member of the Abelisauridae, a group of large theropods that occupied the large predatorial niche in the southern landmasses of Gondwana during the late Cretaceous. Within the Abelisauridae, the genus is often considered a member of the Brachyrostra, a clade of short-snouted forms restricted to South America.
Masiakasaurus is a genus of small predatory noasaurid theropod dinosaurs from the Late Cretaceous of Madagascar. In Malagasy, masiaka means "vicious"; thus, the genus name means "vicious lizard". The type species, Masiakasaurus knopfleri, was named after the musician Mark Knopfler, whose music inspired the expedition crew. It was named in 2001 by Scott D. Sampson, Matthew Carrano, and Catherine A. Forster. Unlike most theropods, the front teeth of M. knopfleri projected forward instead of straight down. This unique dentition suggests that they had a specialized diet, perhaps including fish and other small prey. Other bones of the skeleton indicate that Masiakasaurus were bipedal, with much shorter forelimbs than hindlimbs. M. knopfleri was a small theropod, reaching 1.8–2.1 m (5.9–6.9 ft) long and weighing 20 kg (44 lb).
Rugops is a monospecific genus of basal abelisaurid theropod dinosaur from Niger that lived during the Late Cretaceous period in what is now the Echkar Formation. The type and only species, Rugops primus, is known only from a partial skull. It was named and described in 2004 by Paul Sereno, Jeffery Wilson and Jack Conrad. Rugops has an estimated length of 4.4–5.3 metres and weight of 410 kilograms. The top of its skull bears several pits which correlates with overlaying scale and the front of the snout would have had an armour-like dermis.
Abelisauridae is a family of ceratosaurian theropod dinosaurs. Abelisaurids thrived during the Cretaceous period, on the ancient southern supercontinent of Gondwana, and today their fossil remains are found on the modern continents of Africa and South America, as well as on the Indian subcontinent and the island of Madagascar. Isolated teeth were found in the Late Jurassic of Portugal, and the Late Cretaceous genera Tarascosaurus and Arcovenator have been described in France. Abelisaurids first appear in the fossil record of the early middle Jurassic period, and at least three genera survived until the end of the Mesozoic era 66 million years ago.
Aucasaurus is a genus of medium-sized abelisaurid theropod dinosaur from Argentina that lived during the Late Cretaceous of the Anacleto Formation. It was smaller than the related Carnotaurus, although more derived in some ways, such as its extremely reduced arms and almost total lack of fingers. The type skeleton is complete to the thirteenth caudal vertebra, and so is relatively well understood, and is the most complete abelisaurid yet described. However, the skull is damaged, causing some paleontologists to speculate that it was involved in a fight prior to death.
Abelisauroidea is a diverse superfamily of ceratosaurian dinosaurs, typically regarded as a Cretaceous group, though the earliest abelisaurid remains are known from the Middle Jurassic of Argentina and possibly Madagascar. Possible Abelisauridae remains were also discovered in Late Jurassic Tendaguru Beds in Tanzania.
Ilokelesia is an extinct genus of abelisaurid theropod, preserved in the layers of the earliest Late Cretaceous of the Huincul Formation, Neuquén Group, located near Plaza Huincul, Neuquén Province, Argentina. The specimen, consisting of very fragmentary elements of the skull and the axial and appendicular skeleton, was described by Rodolfo Coria and Leonardo Salgado in late 1998.
Indosaurus is a genus of carnivorous theropod dinosaur that lived in what is now India, about 69 to 66 million years ago during the Maastrichtian division of the Late Cretaceous.
Compsosuchus is a dubious genus of abelisauroid dinosaur from the Late Cretaceous Lameta Formation of India.
Majungasaurus is a genus of abelisaurid theropod dinosaur that lived in Madagascar from 70 to 66 million years ago, at the end of the Cretaceous Period, making it one of the last-known non-avian dinosaurs that went extinct during the Cretaceous–Paleogene extinction event. The genus contains a single species, Majungasaurus crenatissimus. This dinosaur is also called Majungatholus, a name which is considered a junior synonym of Majungasaurus.
Lametasaurus named for the Lameta Formation, Jabalpur, India, is the generic name given to a possibly chimeric dinosaur species. The type species is L. indicus.
The Lameta Formation, also known as the Infratrappean Beds, is a sedimentary geological formation found in Madhya Pradesh, Gujarat, Maharashtra, Telangana, and Andhra Pradesh, India, associated with the Deccan Traps. It is of the Maastrichtian age, and is notable for its dinosaur fossils
Carnotaurinae is a subfamily of the theropod dinosaur family Abelisauridae. It includes the dinosaurs Aucasaurus, Carnotaurus. The group was first proposed by American paleontologist Paul Sereno in 1998, defined as a clade containing all abelisaurids more closely related to Carnotaurus than to Majungasaurus.
Carnotaurini is a tribe of the theropod dinosaur family Abelisauridae from the Late Cretaceous period of Patagonia. It includes the dinosaurs Carnotaurus sastrei; the type species, Aucasaurus garridoi, and Abelisaurus comahuensis. This group was first proposed by paleontologists Rodolfo Coria, Luis Chiappe, and Lowell Dingus in 2002, being defined as a clade containing "Carnotaurus sastrei, Aucasaurus garridoi, their most recent common ancestor, and all of its descendants."
Skorpiovenator is a genus of abelisaurid theropod dinosaur from the Late Cretaceous Huincul Formation of Argentina. It is one of the most complete and informative abelisaurids yet known, described from a nearly complete and articulated skeleton.
Rahiolisaurus is a genus of abelisaurid theropod dinosaur which existed in India during the Late Cretaceous period. It was described in 2010, based on fossils recovered from the Lameta Formation in the Indian state of Gujarat. These fossils include elements from at least seven different individuals and are believed to have been from the Maastrichtian stage, sometime between 72.1 and 66 million years ago, making it one of the last non-avian dinosaurs known in the fossil record. Despite representing a variety of different growth stages, all recovered fossils from the locality indicate a single species, the type species Rahiolisaurus gujaratensis.
Arcovenator is an extinct genus of abelisaurid theropod dinosaurs hailing from the Late Cretaceous of France. The type and only described species is Arcovenator escotae.
Majungasaurinae is a subfamily of large carnivorous theropods from the Upper Cretaceous, found in Madagascar, India, and France. It is a subgroup within the theropod family Abelisauridae, a Gondwanan clade known for their thick and often horned skulls and vestigial arms. The two subfamilies of Abelisauridae are Carnotaurinae, best known from the South American Carnotaurus, and Majungasaurinae, consisting of Madagascar’s Majungasaurus and its closest relatives. Their ancestors emerged in the Middle Jurassic, and the clade lasted until the Upper Cretaceous.
Tralkasaurus is a genus of abelisaurid dinosaur from the Huincul Formation from Río Negro Province in Argentina. The type and only species is Tralkasaurus cuyi, named in 2020 by Mauricio Cerroni and colleagues based on an incomplete skeleton. A medium-sized abelisaurid, Tralkasaurus exhibits a conflicting blend of characteristics found among the early-diverging abelisauroids with others that characterize the highly specialized clade Brachyrostra, and thus its position within the clade is poorly-resolved.
↑ Grillo, O. N.; Delcourt, R. (2016). "Allometry and body length of abelisauroid theropods: Pycnonemosaurus nevesi is the new king". Cretaceous Research. 69: 71–89. doi:10.1016/j.cretres.2016.09.001.
↑ Rogers, Raymond R.; Krause, David W.; Curry Rogers, Kristina; Rasoamiaramanana, Armand H.; Rahantarisoa, Lydia. (2007). Sampson, S. D.; Krause, D. W. (eds.). "Majungasaurus crenatissimus (Theropoda: Abelisauridae) from the Late Cretaceous of Madagascar". Paleoenvironment and Paleoecology of Majungasaurus crenatissimus (Theropoda: Abelisauridae) from the Late Cretaceous of Madagascar. Journal of Vertebrate Paleontology. Society of Vertebrate Paleontology Memoir 8. 27: 21–31. doi:10.1671/0272-4634(2007)27[21:PAPOMC]2.0.CO;2. S2CID130262308.
↑ J.A. Wilson, P.C. Sereno, S. Srivastava, D.K. Bhatt, A. Khosla and A. Sahni, 2003, "A new abelisaurid (Dinosauria, Theropoda) from the Lameta Formation (Cretaceous, Maastrichtian) of India", Contributions from the Museum of Paleontology, University of Michigan31(1): 1-42
1 2 Tortosa, T.; Buffetaut, E.; Vialle, N.; Dutour, Y.; Turini, E.; Cheylan, G. (2014). "A new abelisaurid dinosaur from the Late Cretaceous of southern France: Palaeobiogeographical implications". Annales de Paléontologie. 100 (1): 63–86. Bibcode:2014AnPal.100...63T. doi:10.1016/j.annpal.2013.10.003.
↑ Brookfield, M. E.; Sanhi, A. (1987). "Palaeoenvironments of the Lameta beds (late Cretaceous) at Jabalpur, Madhya Pradesh, India: Soils and biotas of a semi-arid alluvial plain". Cretaceous Research. 8 (1): 1–14. Bibcode:1987CrRes...8....1B. doi:10.1016/0195-6671(87)90008-5.
↑ Mohabey, D. M. (1996). "Depositional environment of Lameta Formation (late Cretaceous) of Nand-Dongargaon inland basin, Maharashtra: the fossil and lithological evidences". Memoirs of the Geological Survey of India. 37: 1–36.
↑ Vianey-Liaud, M.; Khosla, A.; Garcia, G. (2003). "Relationships between European and Indian dinosaur eggs and eggshells of the oofamily Megaloolithidae". Journal of Vertebrate Paleontology. 23 (3): 575–585. doi:10.1671/0272-4634(2003)023[0575:RBEAID]2.0.CO;2. S2CID86208659.
↑ Weishampel, D. B.; Barrett, P. M.; Coria, R.; Le Loeuff, J.; Xijin, Z.; Xing, X.; Sahni, A.; Gomani, E. M. P.; Noto, C. R. (2004). "Dinosaur Distribution". In Weishampel, D. B.; Dodson, P.; Osmólska, H. (eds.). The Dinosauria (2nded.). Berkeley: University of California Press. p.595. ISBN978-0-520-24209-8.
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