| Giganotosaurus Temporal range: Late Cretaceous, 97 Ma |
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|---|---|
| Replica skeleton, Senckenberg Museum | |
| Scientific classification | |
| Phylum: | Chordata |
| Class: | Reptilia |
| Superorder: | Dinosauria |
| Order: | Saurischia |
| Suborder: | Theropoda |
| Family: | †Carcharodontosauridae |
| Genus: | †Giganotosaurus Coria & Salgado, 1995 |
| Species: | †G. carolinii |
| Binomial name | |
| Giganotosaurus carolinii Coria & Salgado, 1995 |
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Giganotosaurus (pronounced /ˌdʒaɪɡəˌnoʊtəˈsɔrəs/ jy-gə-noh-tə-sor-əs)[1] is a genus of carcharodontosaurid dinosaur that lived around 97 million years ago during the early Cenomanian stage of the Late Cretaceous Period.[2] It included some of the largest known terrestrial carnivores, slightly larger than the largest Tyrannosaurus, but smaller than the largest Spinosaurus. Its fossils have been found in Argentina.
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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.[2] The discovery was scientifically reported in 1994.[3] The initial description was published by Rodolfo Coria and Leonardo Salgado in the journal Nature in September 1995.[4] The type species is Giganotosaurus carolinii. The generic name means "giant southern lizard", derived from the Ancient Greek gigas/γίγας meaning "giant", notos/νότος meaning "south wind" and -sauros/-σαύρος meaning "lizard".[5] 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. Various estimates find that it measured somewhere between 12.2 and 13 m (40 and 43 ft) in length, and between 6.5 and 13.3 tons in weight.[6][7][8] A second, more fragmentary, specimen (MUCPv-95) has also been identified, found in 1987 by Jorge Calvo.[9] 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.[10] Giganotosaurus surpassed Tyrannosaurus in mass by at least half a ton (the upper size estimate for T. rex is 9.1 t).[8] Additionally several single teeth, discovered from 1987 onwards, have been referred to the species.
The skull of Giganotosaurus, although large, had a slender, elongated build. It showed rugose areas on the edges of the snout top and above the eye opening. The supratemporal openings were overhung by the edges of the skull roof where the jaw muscles of each side directly attached instead of meeting each other at a midline skull crest. The back of the skull as preserved is strongly inclined forwards, bringing the jaw joints far behind the attachment point of the neck.[2]Giganotosaurus carolinii was slightly larger than Tyrannosaurus rex, but had a brain smaller than those of tyrannosaurids,[11] its size estimated at 275 cm³.[2] The teeth of Tyrannosaurus were longer and wider, and more variable in size. The teeth of Giganotosaurus were shorter, less variable and narrower than those of Tyrannosaurus, and were more adapted for slicing flesh.[12] A well-developed olfactory region, encased in an ossified sphenethmoid, means that it probably had a good sense of smell. Together with these olfactory bulbs, the brain of Giganotosaurus was 18% longer than that of the related large theropod Carcharodontosaurus.[13]
The shoulder blade was very short and thick, with sudden kinks in its shaft. The ischium had a paddle-shaped end; the thigh bone, 143 centimetres long in the holotype, had a head that was pointing relatively upwards.[14] The mid dorsal vertebrae carried rather high spines.
Titanosaur fossils belonging to Andesaurus and Limaysaurus have been recovered near the remains of Giganotosaurus, leading to speculation that these carnivores may have preyed on the giant herbivores. Fossils of the related carcharodontosaurid Mapusaurus grouped closely together may indicate pack hunting, a behavior that could possibly extend to Giganotosaurus itself.
Blanco and Mazzetta (2001) estimated that for Giganotosaurus a growing imbalance when increasing its velocity would pose an upper limit of 14 metres per second (50 km/h; 31 mph) to its running speed, after which minimal stability would have been lost.[15]
In 2005 François Therrien e.a. estimated that the bite force of Giganotosaurus was three times less than that of Tyrannosaurus and that the lower jaws were optimised for inflicting slicing wounds; the point of the mandibula was reinforced to this purpose with a "chin" and broadened to handle smaller prey.[16]
Giganotosaurus, along with relatives like Tyrannotitan, Mapusaurus and Carcharodontosaurus, are members of the carnosaur family Carcharodontosauridae. Both Giganotosaurus and Mapusaurus have been placed in their own subfamily Giganotosaurinae by Coria and Currie in 2006 as more carcharodontosaurid dinosaurs are found and described, allowing interrelationships to be calculated.[6]