Rajasaurus (King Lizard, named after "Raja", a royal title used by South Asian monarchs) is a genus of abelisaurid theropod dinosaur that served as one of the apex predators of the Lameta Formation, India, 69 - 66 million years ago, during the Maastrichtian stage of the Late Cretaceous Period.
Rajasaurus is a medium-sized, heavily-built abelisaurid that stood 2 meters (6 feet, 7 inches) tall. Original estimates give this theropod a length of 11 meters (36 feet) and a mass of 4 metric tons (4.4 short tons).[2] However, revised estimates in 2016 yield an even shorter length of 6.6 meters (22 feet).[1] While there is no confirmed revision of mass, due to being similar in size to its close relative from Madagascar, Majungasaurus, it is likely that Rajasaurus was within a similar weight range, around 750 – 1,100 kilograms (1,650 – 2,430 pounds).[2] Unlike Carnotaurus, which has long, gracile legs that gave it a top speed of around 48 - 56 kilometers (30 - 35 miles) per hour,[5]Rajasaurus and Majungasaurus have short legs, implying that they were slower predators that relied more on ambush, though they may still have been able to accelerate quickly to pursue prey.[4]
Unlike their noasaurid cousins, which retained long forelimbs with well-developed claws, abelisaurids had robust but short arms with immobile elbow joints, no carpalia (wrist bones), metacarpals (palm bones) attached directly to the forearm, and four fused fingers which bear evidence of neither ungual bones nor the grooves and pits of tendon attachments,[6][7] hence, all three of the abelisaurids featured on Prehistoric Planet are portrayed without claws on all four of their immobile fingers. It has been suggested that, at some point in their evolutionary history, the abelisaurid family suffered a genetic defect that caused their HOXA11 and HOXD11 genes (both of which regulate the development of forelimbs) to lose functionality, which resulted in their arms eventually being reduced to stubs, with the entire forelimb past the elbow possibly being vestigial in nature, as the nerve fibers responsible for the transmission of stimuli in these limbs are as reduced as those of emus and kiwis, which bear vestigial wings.[8][6][7][9]
Brain, Senses, and Vocalizations[]
An Isisaurus hatchling sneaks past a Rajasaurus
Not much is found regarding the brain of Rajasaurus, as the only preserved pieces of its braincase are the left sides of the parietal and frontal bones (which are 4 centimeters or 1.6 inches in thickness above the back of the eye socket).[10] Based off of its close relative, Majungasaurus, Rajasaurus was not as intelligent as Carnotaurus, which, in turn, was not as smart as tyrannosaurs.[11][12] Further studies showed that, unlike Carnotaurus and South American abelisaurs, which have large flocculi (the brain lobe responsible for gaze stabilization), Majungasaurus and relatives like Indosaurus of India have small flocculi,[11] Assuming that these findings also prove true for it, this would mean that Rajasaurus did not rely on quick head and body movements to pinpoint prey or other matters of interest, since the diminished size of the flocculus indicates poor coordination of eye movement with head, neck, and body movement.
A Rajasaurus looking and smelling for an Isisaurus hatchling that narrowly escaped
Abelisaurs also possess a poor sense of hearing due to their short lagena (upper extremity of the cochlear duct),[11] hence, Rajasaurus would have had to rely more on detecting low-frequency sounds, and thus likely communicated with low vocalizations. As with Carnotaurus and Majungasaurus, Prehistoric Planet portrays Rajasaurus making guttural crocodile-like sounds and emu-esque vocalizations, producing hisses, huffs, raspy calls, low, rumbling growls and resonant, booming bellows. Much like birds, crocodiles, and other reptiles, Rajasaurus does not need to open its mouth in order to vocalize, as vibrating and amplifying the sound of air within the body is sufficient.
Jaws and Dentition[]
A Rajasaurus snaps up a juvenile Isisaurus
Rajasaurus, like most abelisaurs, had a broad, robust skull that was short yet tall, mounted on a thick, muscular neck.[DN 1] This, along with their extremely reduced forelimbs, indicated that abelisaurs primarily evolved to overpower prey with their jaws. However, up until more up-to-date research concluded otherwise, the forces that even the largest abelisaurs could exert with their jaws were considered weak for their size. While the bite force of Rajasaurus itself was never calculated, according to a study in 2018, abelisaurs may have had a bite force similar to that of Allosaurus, with one abelisaur, Carnotaurus, having an estimated bite force of around 3,341 newtons or 340 kilograms (750 pounds). It is believed that, as with Allosaurus, abelisaurs used their weak bites with their reinforced skulls and strong necks to be able to withstand the stresses of repeatedly grabbing and pulling on large prey like the sauropods they coexisted with.[4] Conversely, estimates made in 2022, based off of phylogenetically predicted physiological cross-sectional areas of jaw adductor muscles, suggest higher bite forces for both Allosaurus and abelisaurids; a Majungasaurus (the closest relative of Rajasaurus involved in the 2022 study) with a skull width of 30 centimeters (12 inches) likely exerted around 3,140 newtons or 320 kilograms (706 pounds) in the front of its jaws, and 7,845 newtons or 800 kilograms (1,764 pounds) in the back of its jaws.[3]
Rugged Features[]
Rajasaurus roars at a rival
As an abelisaur, Rajasaurus had rough skin, made even more rugged by protuberances randomly scattered and distributed all over the body. These large, flat scales, subconical bumps, and studs, fitting the definition of what is known as "feature scales" (specifically of the shield type), lack bony cores or any sort of ossification, and thus cannot be considered as osteoderms.[13][14][15][16][DN 2] It is believed that the rough skin of abelisaurs may have helped these large, highly-active, warm-blooded predators to shed excess heat from their bodies, similar to the integument of living reptiles and mammals.[15]
Atop the theropod's skull, compact and robust like those of other abelisaurs, is a single horn that may either be a display feature or a means of slowly pushing or headbutting rivals. This single horn, along with other shared features, shows that Rajasaurus is more closely related to Majungasaurus of Madagascar rather than Carnotaurus of Argentina, reinforcing the belief that the abelisaurs of Africa, Europe, and India diverged into forms distinct from their isolated South American cousins. Unlike Majungasaurus, however, the horn of Rajasaurus is made of nasal bone more than frontal bone (the inverse is true for Majungasaurus),[17] and it was not extended by thickened skin or a keratinous sheath, unlike what is believed to be the case for the eyebrow horns of Carnotaurus.[4]
Much like Isisaurus with its orange, brown, and white striping and mottling, Prehistoric Planet depicts Rajasaurus with red skin covered in black splotches, a color scheme that, in tandem with its rugged appearance, helps it blend in with the rocky volcanic environment it is found in. It also has black, shiny nictitating membranes, perhaps to help protect the eyes from the heat of volcanic environment it lives in. It shares this trait with the show's depiction of the ankylosaurid Anodontosaurus, which lived in the Horseshoe Canyon Formation in Alberta, Canada, where forest fires can be easily started with a strike of lightning. Rajasaurus was initially designed by Dr. Darren Naish, Prehistoric Planet's lead consultant (who, while discussing about it, shared a joke about how he can only design dinosaurs in black and red), with his vision reworked by Chris Tulloch McCabe.[PhP 1][DN 3]
Rajasaurus is featured as the main - but far from the only - threat of the fifth and final segment of Badlands. As several Isisaurus hatchlings, whose eggs were laid by their mothers months ago in a caldera as shown in the first segment of the episode, were traversing the treacherous volcanic terrain of the Lameta Formation, two of these majungasaurine abelisaurids hunt down and devour several of the young sauropods before briefly crossing paths, with the two predators attempting to intimidate each other. Rajasaurus also appears in "Encounter Dinosaurs", an interactive app on Apple Vision Pro, which shows a Rajasaurus threatening a baby Isisaurus, seeing and interacting with the viewer, and getting into a fight with another Rajasaurus.
A caldera in the Deccan Traps, its toxic gas emissions blown by the monsoon winds
“ In badlands, conditions can change with astonishing speed. Rising summer temperatures fuel electric storms hundreds of miles wide. Here in the Deccan, these seasonal storms cause a shift in the wind direction. And around the caldera where the Isisaur females laid their eggs months ago, the poisonous gases have blown away, providing a critical window of opportunity. ”
Rajasaurus lived 69 - 66 million years ago in the Lameta Formation, an area now known as the Narmada River Valley in the Gujarat State of western India. This area is associated with the Deccan Traps, one of the largest volcanic features on Earth, hence why the abelisaurs are seen hunting in a rugged volcanic field. The Lameta Formation is also interpreted as a semi-arid landscape, though later, more recent studies suggest that it is more of a tropical humid region with rivers, lakes,[18][19] and, as shown on Prehistoric Planet, forests past the jagged terrain of the central Indian badlands. The intense volcanic activity of the Deccan Traps by that time, combined with the tropical climate of the area, subjected Late Cretaceous central India to rainfall of around 1,760 - 1,860 millimeters (69.3 - 73.3 inches) per year, higher than the annual precipitation of modern-day India during a monsoon, around 1,200 millimeters (47.2 inches).[20]
A trench in the Deccan Traps, where small creatures can hide in to escape from predators
“ Now the wind has cleared the toxic gases, the door opens... for predators. ”
These events and conditions, though hostile and threatening, also provide opportunities for predator and prey alike. For Isisaurus and India's other titanosaurs, the Deccan provides heated sand where they can lay their eggs in, just as iguanas of the volcanic Galapagos Islands do today,[21] with the toxic gases acting as a natural barrier that temporarily protects their eggs and young. For Rajasaurus, the formation of the volcanic terrain sets up a treacherous area that some prey animals may not be able to easily traverse, and the region provides plenty of cover for small prey and nimble ambush predators to hide in.
Paleofauna[]
Two Rajasaurus hunt down Isisaurus hatchlings
The Lameta Formation is known as the nesting grounds of titanosaurs like Isisaurus, Jainosaurus, and the dubious Titanosaurus, with evidence showing that the animals used the geothermally-heated volcanic sand of the region to incubate their eggs.[22][PhP 2] These sauropods serve as prey for Rajasaurus, which is larger than most of the other abelisaurs in the area, like Indosaurus, Indosuchus, and the potentially-dubious Lametasaurus. One abelisaur in the area, Rahiolisaurus gujaratensis, was originally estimated to be larger than Rajasaurus, with a length of 8 meters (26 feet) and 2 metric tons (2.2 short tons),[23][2] but allometry-based estimates revised its length as 6.22 - 6.75 meters (20 feet, 5 inches - 22 feet, 2 inches),[1] and it has slender arms and an overall sleeker build compared to Rajasaurus.[23] Other animals in the region include noasaurids like Laevisuchus and the dubious Compsosuchus, possible ornithischians (including one mistaken for a late-surviving stegosaur), snakes like Madtsoia and its relative Sanajeh, and the side-necked turtle Jainemys.
Rajasaurus and its contemporaries were among the last non-avian dinosaurs on Earth prior to the Cretaceous-Paleogene Extinction Event, a catastrophe that wiped out three-quarters of life on Earth. However, at least one study theorizes that all Indian non-avian dinosaurs may have actually been killed off by a massive eruption in the Deccan Traps 350,000 years before the arrival of the asteroid that wiped out the non-avian dinosaurs.[24]
Hunting Tactics, Feeding Preferences, and Competitive Behavior[]
Two Rajasaurus being hostile to one another
“ A Rajasaur. With so many babies out in the open, this could be a feast. ”
As is expected of most predators, Rajasauruses demonstrate some intelligence when it comes to hunting and feeding. The hunters seem to be aware of when the poisonous gases that normally fill the Deccan Traps are momentarily cleared by seasonal winds, taking it as the opportunity to hunt other creatures that also take advantage of this event, like newly-hatched Isisauruses. While abelisaurs are believed to be ambush hunters, the Rajasauruses forego that tactic entirely when pursuing what they view as plentiful, defenseless prey, putting on decent speed and agility to quickly navigate through the jagged rocks of the rugged, uneven terrain and easily pick off dozens of hatchlings.
The Rajasauruses are also shown to be hostile against each other, as shown when two individuals briefly get into a roaring fight in the fifth segment of Badlands, either due to territorial reasons or conflict over who gets priority to feed on the Isisaurus hatchlings even while there's still many of them. A similar altercation is depicted in the interactive Apple Vision Pro app "Encounter Dinosaurs".
Gallery[]
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↑Vargas, A. 2002. "La extrema reducción del radio y la ulna en la evolución de Carnotaurus sastrei: Posible pérdida de función de los genes HOXA11 y HOXD11". Ameghiniana 39: 17R
