Giganotosaurus

Giganotosaurus was a genus of large carcharodontosaurid dinosaur native to South America in the late Cretaceous period, approximately 97 million years ago. It was among the largest of the allosauroids (along with Carcharodontosaurus and Mapusaurus), and comparable in size to Tyrannosaurus. Its fossil remains are known exclusively from Argentina.

Giganotosaurus is a well-known theropod, and like Tyrannosaurus and Carcharodontosaurus it often is referred to as the largest theropod. However it is in fact smaller than the African Spinosaurus, to which it is only distantly related.

Discovery and fossil record
The most complete find of Giganotosaurus was made by Rubén Dario Carolini, an amateur fossil hunter who, on 25 July 1993, discovered a skeleton in deposits of Patagonia (southern Argentina) in what is now considered the Candeleros Formation. The discovery was scientifically reported in 1994. The initial description was published by Rodolfo Coria and Leonardo Salgado in the journal Nature in September 1995. The type species is Giganotosaurus carolinii. The generic name means "giant southern reptile", derived from the Ancient Greek gigas meaning "giant", notos meaning "south wind" and -sauros meaning "reptile". The specific name honours Carolini.

The holotype specimen's (MUCPv-Ch1) skeleton was about 70% complete and included parts of the skull, a lower jaw, pelvis, hindlimbs and most of the backbone<. The premaxillae, jugals, quadratojugals, the back of the lower jaws and the forelimbs are missing. A second, more fragmentary, specimen (MUCPv-95) has also been identified, found in 1987 by Jorge Calvo.It is only known from the front part of the left dentary which is 8% larger than the equivalent bone from the holotype. This largest Giganotosaurus specimen is estimated to represent an individual with a skull length of 195 cm (6.40 ft), compared to the holotype's estimated at 1.80 m (5.9 ft) skull, making it likely that Giganotosaurus had the largest skull of any known theropod.

Description and Paleobiology
Giganotosaurus is known from two specimens, both of which indicate that it was a very large theropod. The type specimen, MUCPv-Ch1, is estimated to be 12.4 metres in length and roughly 7 tons in weight; while the larger MUCPv-95 is estimated at 13.2 metres long and 8.2 to 9.1 tons in weight, making it slightly larger than Tyrannosaurus.

Giganotosaurus was fairly lightly built, with long, powerful legs that may have permitted swift running. The front legs are fairly large for a theropod, and have three fingers, each ending in hooked claws. Unlike Spinosaurus and related genera, however, Giganotosaurus probably did not use its claws as weapons. The tail is long and tapering, as in most theropods, and the body is deep but surprisingly slender. At the end of a short neck, Giganotosaurus possessed a massive head with scissor-shaped jaws. The eyes were positioned on the side of the head, giving it good peripheral vision but reducing its binocular vision. The jaws were scissor-shaped, and could open extremely wide. This gave it a wide gape, but sacrificed bite force. The teeth were thin and serrated, and well-adapted to slicing through flesh, but not for crunching bones. For this reason, it is believed that Giganotosaurus hunted sauropods, which had bones what would have been nearly impossible to break. Canadian paleontologist Phil Currie believes that Giganotosaurus would have gathered to mob sauropods, with individuals distracting sauropods while others attacked from other angles and bit off pieces of flesh. If this is true, it would indicate some degree of social behaviour in Giganotosaurus. Other paleontologists, such as Thomas Holtz, believe that sauropods would have been too large for Giganotosaurus to hunt and would have instead attacked iguanodonts and other ornithopods.

Giganotosaurus is very similar to the a lighty longer Mapusaurus and the slightly smaller Carcharodontosaurus. The three genera are closely related to one another and are separated by only minimal differences. The skull of Giganotosaurus is more elongated than that of Carcharodontosaurus and notaceably larger. It also has temporal fenestrae that are larger than the temporal fenestrae of Carcharodontosaurus. There are even fewer differences between Giganotosaurus and Mapusaurus, and the two genera have been put into their own subfamily of the family Carcharodontosauridae, known as the Giganotosaurinae.

Behaviour
Giganotosaurus behaviour is a matter of debate. It is thought to have been a predator because of its blade-like teeth which were adapted for slicing through flesh. However, a few paleontologists believe that Giganotosaurus was a scavenger. Some paleontologists believe that all large theropods were too large and heavy to chase after prey, and would have fed exclusively on carrion, though this seems highly unlikely.

Bones of Mapusaurus have been found in a mass gathering in Patagonia, Argentina, with no fossils of other species among them, suggesting that these animals were pack hunters, or at least had some form of social behaviour. This behaviour could possibly have extended to other carcharodontosaurids, particularly Giganotosaurus, as it is the closest relative of Mapusaurus and therefore the most likely to demonstrate similar behaviour.

In popular culture
The discovery of Giganotosaurus caused a massive hype leading many to call it the largest theropod, but the seemingly forgotten Spinosaurus was larger still. Giganotosaurus is a fairly well-known dinosaur, appearing in many books and in television series such as Walking with Dinosaurs, where it was depicted as being 14 metres long and hunting the giant sauropod Argentinosaurus. A Giganotosaurus also serves as the main antagonist of the video game Dino Crisis 2, though it is extremely oversized, being comparable in size to Spinosaurus. Giganotosaurus in Dino Crisis 2 was also depicted as being able to pick up and throw an adult Tyrannosaurus.