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Giganotosaurus: Facts About the 'Giant Southern Lizard'

Giganotosaurus was one of the largest meat-eating dinosaurs. It roamed modern-day Argentina during the late Cretaceous Period, about 99.6 to 97 million years ago.

For a long time, Tyrannosaurus rex — "king of the dinosaurs" — was thought to be the largest carnivorous dinosaur. Today, Giganotosaurus is believed to have been slightly larger than T. Rex, though even Giganotosaurus ranks behind Spinosaurus in size among the meat-eating dinosaurs.

Giganotosaurus vs. Spinosaurus vs. Tyrannosaurus

None of these dinosaurs lived at the same time — or in the same area. Here is a comparison:

 
spinosaurus
Giganotosaurus Spinosaurus Tyrannosaurus
Lived 99.6 to 97 mya in South America Lived 112-97 mya in North Africa Lived 67 to 65 mya in North America and Mongolia
40-43 feet long At least 50 feet long 40 feet long
Weighed up to nearly 14 tons Weighed up to 23 tons Weighed up to 9 tons
Huge skull with sharp teeth; short arms and three-fingered, clawed hands Long spines on back; long, narrow snout; powerful jaws with needle-like teeth Strong back legs; tiny forearms; massive, thick skull; powerful jaws with serrated teeth

But even Spinosaurus was dwarfed by some of the long-necked herbivorous sauropods, which are the largest dinosaurs known to have existed.

Big, strong and fast

Pronounced jig-a-NOT-o-SOR-us, Greek for "giant southern lizard," the dinosaur is a member of the Carcharodontosauridae ("shark-toothed lizards") family. There is only one known species of the dinosaur: Giganotosaurus carolinii. It lived from 99.6 to 97 million years ago, during the early Cenomanian stage of the Late Cretaceous Period, or about about 30 million years before T. rex.

First described in a 1995 study in the journal Nature, Giganotosaurus was, at the time, thought to be the largest carnivorous dinosaur. The specimen analyzed was up to 41 feet long (12.5 meters) from head to tail, and weighed between 6.6 and 8.8 tons (6 to 8 metric tons), the researchers estimated. 

Calculating mass from fossils is notoriously difficult, and a more recent estimate published in 2007 in the Journal of Vertebrate Paleontology suggests Giganotosaurusweighed up to 15 tons (13.8 metric tons). Additionally, scientists have discovered a partial Giganotosaurus jawbone that's 8 percent larger than the corresponding bone of the original specimen, according to a 1998 article in the journal Gaia. Estimates based on this skull fragment suggest the dinosaur may have been up to 43 feet (13.2 m) long, 

Giganotosaurus walked upright on two large and powerful legs. It may have been fairly agile, thanks to its thin, pointed tail, which may have provided balance and the ability to make quick turns while running. 

Models suggest that Giganotosaurus could run up to 31.3 mph (50.4 km/h), according to a 2001 article in the journal Acta Palaeontologica Polonica. Any faster and the animal would lose its stability and fall over. By comparison, a 2011 study in the journal PLOS ONE computed the maximum running speed of T. Rexto be 25 mph (40 km/h).

Like other carcharodontosaurids, which includes Mapusaurus and Carcharodontosaurus, Giganotosaurus had two short arms with sharp claws on the end of its three-fingered "hands." However, carcharodontosaurid forelimbs have been poorly preserved, so the anatomy of Giganotosaurus' arms is not well understood.

This makes it difficult to hypothesize about what the dinosaur could do with its appendages, said Juan Canale, a paleontologist with Argentina's National Scientific and Technical Research Council (CONICET). "We have to wait for more complete fossils!" he said.

Giganotosaurus had a massive skull to go with its large body. The skull of the Giganotosaurus holotype — the specimen formally described in 1995, upon which the species is based— was 5.2 feet (1.6 m) long, according to a 2003 article in the Journal of Vertebrate Paleontology. The endocast (internal cast of the braincase) of the holotype is some 19 percent longer than the endocast of its comparably sized relative, Carcharodontosaurus saharicus; however, the endocast volume of Tyrannosaurus is still larger, suggesting Giganotosaurus had a smaller brain than its popular, distant cousin, the study notes.

What did Giganotosaurus eat?

Scientists believe that Giganotosaurus survived mostly on large herbivore dinosaurs. Because of its size, it did not have any natural predators.

Giganotosaurus had the capability of killing live prey. Of course, like T. rex, Velociraptor and other carnivorous dinosaurs, Giganotosaurus was likely an opportunistic carnivore that also scavenged if necessary.

Giganotosaurus had the same flat, serrated teeth that are characteristic of other carcharodontosaurids, which would have allowed it to easily slice through the flesh of its prey. Some estimates propose that the dinosaur had a bite force several times weaker than that of T. rex, which suggests Giganotosaurus may have hunted by inflicting slicing wounds instead of biting — a tactic that would have allowed it to take down very large prey that it couldn't have gotten its jaws around.

In fact, at a 2014 paleontological meeting, Canale and his colleagues presented evidence of carcharodontosaurid teeth associated with the remains of the titanosaur saruopod Argentinosaurus, the largest land animal ever found. But whether or not the carnivores took down their giant prey alone is unclear. "It is possible that carcharodontosaurids hunted in packs," Canale said.

In 2006, seven fossils of the carcharodontosaurid Mapusaurus have been found grouped closely together in a single bonebed, according to a study in the journal Geodiversitas. "There are no doubts that this is not casual, they died together because they lived as a group," Canale said. This group-living behavior and possible pack hunting may have extended to Mapusaurus' close relatives, including Giganotosaurus, he said.

Aside from titanosaurs, Giganotosaurus probably also fed on rebbachisaurid sauropods, which were quite abundant in the Cenomanian times, Canale said, adding that scientists haven't found direct evidence of this predator-prey interaction yet.

Fossil finds

In 1993, Rubén Dario Carolini, an amateur dinosaur hunter, discovered Giganotosaurus in the Neuquén Province of Patagonia (southern Argentina). The fossils came from deposits in a region that is now referred to as the Candeleros Formation. The skeleton was about 70 percent complete and included parts of the skull, pelvis, leg bones and backbone. 

Paleontologists Rodolfo Coria and Leonardo Salgado named Giganotosaurus in 1995 when they described the dinosaur in their Nature study. The species name, Giganotosaurus carolinii, honors Carolini.

In 1988, Argentine geologist and paleontologist Jorge Orlando Calvo discovered a second Giganotosaurus specimen, which consisted of the front part of the left lower jaw.

While the remains of many other dinosaurs have been discovered at various stages of development (young, juveniles and full-grown adults), the same cannot be said of Giganotosaurus. Additionally, no complete skeleton of a Giganotosaurus has been found.

Giganotosaurus should not be confused with Gigantosaurus, a lesser-known sauropod discovered in England.

Infographic: Dinosaur profile of the giant carnivorous dinosaur Giganotosaurus.

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