Abelisaurus

Abelisaurus was a theropod that used to live in South American woodlands during the late Cretaceous period, i.e. some 85-80 million years ago. Abelisaurus is actually a Greek name for Abel's Lizard. This dinosaur was named Abel's Lizard because its remains were discovered by Roberto Abel, an Argentinian paleontologist. It is estimated that this dinosaur measured around 30 feet in length and weighed around 2 tons. Considering the behemoth sizes of other dinosaurs, 2 tons is actually a lightweight candidate but is enough to crush humans. Abelisaurus had a large head with small teeth. However, the most notable feature of the head was the presence of a collection of large holes on the skull right above the jaws. Though the exact reason for these holes are not known, scientists believe that they might have been caused by the process of evolution. It was actually a balancing act. The skull being massive, the absence of these holes could simply unbalanced the entire body weight of the dinosaur. An interesting fact about Abelisaurus is that it is known by only one skull. Put in other words, only the skull was found and the rest of the carnivore was reconstructed using that skull. Scientific studies led to the belief that Abelisaurus were scaled-down or smaller versions of Tyrannosaurus rex. Abelisaurus used to have bipedal locomotion and had very short arms that literally didn’t help much in any activity like eating, hunting, running etc.

Abelisaurus actually gave its name to an entire theropod dinosaur family. The family is known as “Abelisaurs”. Abelisaurs (Abelisauria) as a whole lived in Gondwana Island Continent during the Cretaceous period. Today that area actually consists of South America, Madagascar and Africa. Abelisauria ncludes other efficient carnivore dinosaurs like Majungatholus and Carnotaurus. Abelisaurs flourished in the Southern hemisphere during the Cretaceous period, but their origins can be traced back to at least the Middle Jurassic, when they had a more global distribution (the earliest known abelisaur remains come from Australian and South American deposits dated to about 170 million years ago). By the Cretaceous period, abelisaurs had apparently become extinct in Asia and North America, possibly due to competition from tyrannosaurs. However, advanced abelisaurs of the family Abelisauridae persisted in the southern continents until the Cretaceous–Paleogene extinction event 66 million years ago. Like most theropods, abelisaurids were carnivorous bipeds. They were characterized by stocky hindlimbs and extensive ornamentation of the skull bones, with grooves and pits. In many abelisaurids, like Carnotaurus, the forelimbs are vestigial, the skull is shorter and bony crests grow above the eyes. Most of the known abelisaurids would have been between 5 and 9 meters (17 to 30 ft) in length, from snout to tip of tail, with a new and as yet unnamed specimen from northwestern Turkana in Kenya, Africa reaching a possible length of 11–12 meters (36 to 39 feet). Before becoming well known, fragmentary abelisaurid remains were occasionally misidentified as possible South American tyrannosaurids.

Coining the type species Abelisaurus comahuensis, both genus and species were named and described by Argentine paleontologists José Bonaparte and Fernando Emilio Novas in 1985. The generic name recognizes Roberto Abel as the discoverer of the type specimen, and also as the former director of the provincial Museum of Cipolletti in Argentina, where the specimen is housed. It also incorporates the Greek σαυρος/sauros, meaning 'lizard'. The specific name comahuensis honors the Comahue region of Argentina, where the fossil was found.The holotype, MC 11078, was in 1983 uncovered at the "Cantera de la Pala Mécanica"-site in the Lago Pellegrini quarries exploited by Abel since 1975. This single known fossil of Abelisaurus consists of a skull, lacking the lower jaws, that is incomplete, especially on the right side. Most of the connections between the snout and the back of the skull are absent. It is also missing most of the palate (roof of the mouth). Despite the missing pieces, it could be estimated at over 85 centimetres (33 in) long. Abelisaurus is one of the many dinosaurs that have been discovered in Patagonia. It was originally described as coming from the Allen Formation but subsequent research proved the remains were actually found in the older Anacleto Formation (part of the Neuquén Group) of Rio Negro Province, Argentina. The Anacleto is a geologic formation in South America, dating from the early Campanian stage of the Late Cretaceous Period, between 83 and 80 million years ago.

In 2009, Novas suggested that Aucasaurus garridoi might be a junior synonym of Abelisaurus. In 2010, Gregory S. Paul renamed Aucasaurus into a Abelisaurus garridoi. This has found no acceptance. Aucasaurus short, deep-snouted skull was not as short or as deep-snouted as that of Carnotaurus. Also, instead of horns, it had a pair of low ridges above each eye. In 2010, Gregory S. Paul estimated its body length at 5.5 metres, its weight at 700 kilograms. In 2016, its length was estimated to be 6.1 metres (20 ft) in a comprehensive analysis of abelisaur size. A possible braincase of Abelisaurus (or Carnotaurus) in 2011 and was studied in 2015 by Ariana Paulina-Carabajal and Cecilia Succar, in which the skull material was scanned using a medical CT machine. Virtual three-dimensional inner ear and cranial endocasts were obtained and visualized using the imagine software at the University of Alberta. A latex cranial endocast was also made. The forebrain, midbrain, and hindbrain  resemble  the  morphology  described  for  the  abelisaurids Majungasaurus and Indosaurus. However, Abelisaurusexhibits a floccular process that is relatively larger than that of Majungasaurus. In Abelisaurus the flocculus is enclosed in  an  8-shaped  floccular  recess,  similar  in  shape and size to that observed in  Carnotaurus and Aucasaurus, suggesting that the two Patagonian taxa were capable of a slightly wider range of movements of the head. The labyrinth of the inner ear is similar in shape and size to the semicircular canals of Majungasaurus, although  the  lateral  semicircular  canal  is  shorter in Abelisaurus.