Giganotosaurus

Kingdom: Animalia

Phylum: Chordata

Class: Reptilia

Order: Saurischia

Family: Carcharodontosauridae

Genus: Giganotosaurus

Species: Giganotosaurus carolinii

Introduction

The discovery of Giganotosaurus in 1995 presented a rival for Tyrannosaurus for the title of largest carnivore. Although there is still a great deal of debate regarding what species is the largest carnivore, as specimens for some dinosaurs such as Giganotosaurus remained limited for establishing overall and average size, Giganotosaurus is considered one of the largest carnivores ever discovered. Giganotosaurus is also considered to have lived during the time and in the place of the “land of the giants,” a region that now encompasses Argentina. This area was home to not only Giganotosaurus, but also some of the largest ever known herbivores, including Argentinosaurus.

Classification

Paleontologists use two major systems for classifying organisms. Linnaean taxonomy uses overall physical similarity to place organisms into different groups. By contrast, cladistics seeks to create groups of organisms based on evolutionary relationships; these groups are called “clades.” Cladistic analysis focuses on important key traits and attempts to trace the inheritance of a trait among descendants of a common ancestor.

Under the Linnaean system, Giganotosaurus falls under the Saurischia (“bird-hipped”) order, which comprises two major suborders: the large, herbivorous Sauropoda and the predominately carnivorous Theropoda, under which Giganotosaurus falls. The dinosaur is further classified under the Carcharodontosauridae (“shark-toothed lizards”) family, which includes some of the largest carnosaurs that ever existed, such as Carcharodontosaurus, Tyrannotitan, and Mapusaurus. Some researchers also believed that Giganotosaurus and Mapusaurus should be further classified into the Giganotosaurinae subfamily, to highlight their close relationship. Until more remains are found, however, dinosaur classification remains problematic.

A cladistic analysis places Giganotosaurus in the most advanced theropod clade, Tetanurae, which are characterized by their “stiff tails.” These species are considered more closely related to birds than to ceratosaurs. A cladistic analysis would also place Giganotosaurus under the Carcharodontosauridae (“shark-toothed lizards”) clade.

Anatomy

For many years, Tyrannosaurus was the unrivaled king of the carnivorous dinosaurs. However, the Giganotosaurus and Spinosaurus became rivals for largest carnivorous dinosaur ever found. While Spinosaurus may have been longer, Giganotosaurus was likely heavier and had one of the largest skulls of any theropod ever unearthed at that point. Estimates of length vary from 13 to 14 meters (42.5–46 feet), and its skull measured up to 1.95 meters (6.5 ft) long.

Giganotosaurus possessed the same general body characteristics of all bipedal theropods. It had a very large head, deep chest, and long, tapered tail. Its massive and powerful rear legs ended in three-clawed feet, and its small fore-arms ended in three-clawed fingers.

As with all theropod species, the greatly reduced forearms of Giganotosaurus meant that it relied heavily on its back legs for speed and bipedal locomotion, with its long tail providing support and balance.

Giganotosaurus also possessed a relatively short but deep jaw with arrow-shaped serrated teeth, which were more than 20 centimeters (7.8 in) long and were used to tear flesh from their prey. Although Giganotosaurus had forward-facing eye-sockets to help it hunt, it more likely relied on smell for success. It had very large olfactory bones, which indicate that this species had a very strong sense of smell.

Intelligence

The encephalization quotient (EQ) is used to determine animal intelligence and is defined as the ratio between body and brain size. This figure can reach up to 5.8 in dinosaurs; however, most dinosaurs fall within a range of 0.1 to 2.0 on a scale that extends to an upper limit of 8.0, the approximate value calculated for the human brain. Although modern day animals are considered to be of much greater intelligence than prehistoric dinosaurs, there is growing evidence that dinosaurs may have been more intelligent than first thought.

Although Giganotosaurus was larger than Tyrannosaurus and possessed a massive skull, its brain was smaller. It was, like all carnosaurs, at the higher end of dinosaur intelligence with an EQ score falling between 1.0–1.9, although its smaller brain case meant it likely fell at the lower end of this scale. Paleontological theory states that carnivorous dinosaurs possessed greater intelligence than their herbivorous cousins. This is related to their requirement for greater cognitive capability and behavioral flexibility to successfully hunt.

Reproduction and Population

Population numbers for prehistoric animal species is difficult to determine due to the incomplete fossil record. As only a few specimens have been found for Giganotosaurus, accurately estimating the extent of their population and range is problematic. It is believed, however, that their distribution was restricted to regions within what is now Argentina in South America.

Reproductive behavior is also difficult to determine for ancient animals. Most dinosaurs, including Giganotosaurus, were oviparous and laid several eggs per clutch. Although most dinosaurs appear to lay eggs, the methods differed. Some species laid eggs in nests, others buried eggs underground, several brooded their eggs, and other appeared to use communal nesting sites. While post egg-laying care has been seen in some species, evidence for post-hatching parental care remains inconclusive for many species. Paleontologists believe, however, that such behavior is possible, even probable, for some dinosaur species.

Diet

Giganotosaurus was a carnivorous species that hunted and consumed other dinosaurs. It is considered likely that it preyed on the herbivorous dinosaurs that lived in the same region and at the same time. In particular, massive plant eaters, such as Chubutisaurus, Saltasaurus, Janenschia and Argentinosaurus, were likely prey species for Giganotosaurus. Its teeth were sharp and serrated, and researchers believe that Giganotosaurus would have been able to use its teeth to slice flesh more effectively than other predators, such as Tyrannosaurus, which crunched bones. However, it is still considered likely that Giganotosaurus would have had to “grip-and-rip” its prey. This approach to feeding meant that the skull not only had to be strong, it also had to withstand a tremendous bite force and the stress caused by struggling prey.

As with later predators such as Tyrannosaurus, there is continuing debate regarding whether Giganotosaurus was an active hunting predator or an opportunistic carrion scavenger. Many paleontologists consider that it was likely both—hunting when required and scavenging if the opportunity presented itself.

Behavior

Prehistoric behavior is one of the most difficult areas for paleontologists to determine. Gaps in the fossil record and limits to the amount of information that can be obtained from fossilized remains mean that researchers base scientific hypotheses on the behavior of extant animals that share a similar ecological niche to extinct species.

While scientists know that Giganotosaurus was a carnivore, evidence remains unclear as to how it hunted. Some species are thought to have hunted in packs while others are presumed to have been solitary predators. It is also still unclear whether Giganotosaurus was a pure hunter or an opportunistic scavenger, which would certainly influence much of its behavior. While evidence from similar species indicates that Giganotosaurus would have been able to run, questions persist as to whether it chased prey for extended periods or ambushed prey with a swift sprint. In addition, if it was a scavenger, did it follow the herds of migrating herbivores waiting for easy or sick victims? Until more remains are found, such questions will remain unanswered.

Habitat and Other Life Forms

Although the Late Cretaceous was generally characterized by a cooling climate, without the existence of polar ice caps, it was warmer than modern day. The climate of the Late Cretaceous has, in fact, been described as a “greenhouse climate” with little change in the thermal gradient from the equator to the poles. While many areas of the world were still dominated by gymnosperm vegetation, the Late Cretaceous was also characterized by the rapid radiation and diversification of angiosperms.

The discovery of plant eating rebbachisaurs and crocodiles from the same period as Giganotosaurus are similar to discoveries in Africa. This has led some researchers to state that South America and Africa were still connected land masses 100 million years ago. This throws into doubt when the separation of these land masses occurred (through continental drift), perhaps more than 10 million years later than current theory states. Such information suggests that radiation and evolution of dinosaurs may have been centered in the Southern rather than Northern Hemisphere as first thought.

Although they both lived during the Late Cretaceous period and are often discussed and compared, both Tyrannosaurus and Giganotosaurus were separated by about 20 to 25 million years and lived on two different continents. Giganotosaurus was found in the Rio Limay Formation in the Provincia de Neuquen of Argentina, often claimed to be the time and place of the “land of the giants.” Other species that have been found in the same formation include Anabisetia saldiviai, Andesaurus delgadoi, Argentinosaurus huinculensis, Ilokelesia aguadagrandensis, Mapusaurus roseae, and Rebbachisaurus tessonei. Massive plant eaters, such as Chubutisaurus, Saltasaurus, and Argentinosaurus, were likely prey species for Giganotosaurus, which shared the South American landscape with other predators such as Carotaurus.

Research

Giganotosaurus was discovered in 1994. An amateur fossil hunter by the name of Ruben Carolini discovered the remains of a massive dinosaur in Patagonia, a region of Argentina in South America. Almost 70 percent of this new predator's skeleton appeared to be preserved. A team from the Carmen Funes Museum in Neuquen, led by paleontologist Rodolfo Coria, was called to excavate the fossil. In 1995, Coria described and named the specimen, Giganotosaurus carolinii, for the man who had first discovered it.

It was only after the 1994 find that an earlier fossil discovered in Argentina in 1987 by Coria could be identified. Although it was only a partial and isolated dentary specimen, it was already known to be from a large theropod. However, the discovery of Giganotosaurus in 1994 helped identify the earlier find as being from the same species. This was significant as it showed that Giganotosaurus was even larger than first thought and was one of the largest carnivorous dinosaurs ever found.

As many discussions of dinosaurs into the twenty-first century continued to focus, in part, on their potential size, museums and other educational institutions increasingly sought to enlighten more of the public about the information that had been gathered about some of the biggest dinosaurs studied, particularly those outside of the still largely best-known Tyrannosaurus. In 2019, the Giganotosaurus was one of the large carnivorous dinosaurs prominently featured via reconstruction in a special, technologically integrative exhibit at the Cleveland Museum of Natural History.

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