Abelisaurus

The large theropod ***Abelisaurus comahuensis*** was similar to *Albertosaurus* from Alberta, Canada especially in it's size and lifestyle. It was a bipedal carnivore that probably reached 7 to 9 meters (25 to 30 feet) in length, although it is known from only one partial skull. But it's skull led two Argentinian paleontologists to put it in it's own family now known as the Abelisaurida. It lived in Argentina during the Late Cretaceous, 70 to 66 million years ago.

## Discovery and naming

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.

## Description

As only the skull is known, it has proven difficult to provide a reliable size estimate of *Abelisaurus*. It has transpired that abelisaurids have relatively short heads. In 2010, Gregory S. Paul estimated its body length at ten metres (32 ft 10 in), its weight at 3 tonnes (3 long tons; 3 short tons). In 2012 Thomas Holtz gave a possible length of 11 metres (36.3 feet). In 2016, its length was estimated to be 7.4 metres (24 ft 3 in) in a comprehensive analysis of abelisaur size. Others authors gave a similar size at 7.2 metres (23.6 feet) and 1.65 tonnes (1.82 short tons).

Skull length was estimated at 85 centimetres (33 1⁄2 in) in 1985. The skull is relatively deep. Although there are no bony crests or horns, like those found in some other abelisaurids, such as *Carnotaurus*, rough ridges on the snout and above the eyes might have supported some kind of crest made out of keratin, which would not have become fossilized. The skull roof is thickened. There are also very large *fenestrae* (window-like openings) in the skull, which are found in many dinosaurs and reduce skull weight. One of these is a large triangular antorbital fenestra in the side of the snout. The eye socket behind it is rather high. It is constricted in the middle by bony projections of the lacrimal bone in the front and the postorbital bone at the rear. The eye was located above the constriction. Behind the eye socket a large triangular infratemporal fenestra is present. Its form reflects a strong forward inclination of the back of the skull. The front snout bone, the praemaxilla, bore four relatively small teeth. The maxilla behind it had at least seven, but perhaps as many as thirteen, larger teeth.

## Classification

*Abelisaurus* in the newly created family Abelisauridae in 1985. They thought it was a member of the Carnosauria. *Abelisaurus* was the first abelisaurid named. Many other abelisaurids have since been discovered, including much more complete specimens of *Aucasaurus*, *Carnotaurus* and *Majungasaurus*. They showed that abelisaurids were not carnosaurs in the modern sense, but belonged to the Neoceratosauria instead. Some scientists place *Abelisaurus* as a basal abelisaurid, outside the subfamily Carnotaurinae. Others are less certain of its position. *Abelisaurus* shares some skull features, such as a relative elongation, with the carcharodontosaurids, a group unrelated to other species assigned to the Abelisauridae, and, since it is known only from a skull, it has been suggested that future discoveries may show that *Abelisaurus* was in fact a carcharodontosaurid. However, this is thought unlikely.

## Paleobiology

It has been considered to be more closely related to theropod *Ceratosaurus* from the Jurassic Period. Only the skull of *Abelisaurus* been found, but its body proportions were probably similar to other large theropods with the same size skulls (three feet long). *Carnotaurus* had slender legs with the front shorter than the back. Since *Carnotaurus* probably was an early abelisaurid, scientists suppose that Abelisaurus also had short front limbs and slender legs. Other details of its body are unknown. The discovery of *Abelisaurus* is important because it shed light on many different southern-hemisphere theropods that are known only from fragmentary and puzzling material. These remains were difficutlt to identify and were occasionally used to suggest that late Cretaceous tyrannosaurids fromt the northern hemisphere were in the southern hemisphere. Now that good abelisaurid material has been discovered and described, sceintists have learned that many of those remains were abelisaurids. The possibility of southern-hemisphere tyrannosaurids is less likely.