Sinraptor by the paleontologist Thomas R. Holtz and colleagues in 2004. In 2006, Coria and Currie united Giganotosaurus and Mapusaurus in the carcharodontosaurid subfamily Giganotosaurinae based on shared features of the femur, such as a weak fourth trochanter, and a shallow, broad groove on the lower end. In 2008, Sereno and the paleontologist Stephen L. Brusatte united Giganotosaurus, Mapusaurus, and Tyrannotitan in the tribe Giganotosaurini. In 2010, Paul listed Giganotosaurus as "Giganotosaurus (or Carcharodontosaurus) carolinii" without elaboration. Giganotosaurus is one of the most complete and informative members of Carcharodontosauridae. The following cladogram shows the placement of Giganotosaurus within Carcharodontosauridae according to Sebastián Apesteguía et al., 2016: Evolution Coria and Salgado suggested that the convergent evolution of gigantism in theropods could have been linked to common conditions in their environments or ecosystems. Sereno and colleagues found that the presence of carcharodontosaurids in Africa (Carcharodontosaurus), North America (Acrocanthosaurus), and South America (Giganotosaurus), showed the group had a transcontinental distribution by the Early Cretaceous period. Dispersal routes between the northern and southern continents appear to have been severed by ocean barriers in the Late Cretaceous, which led to more distinct, provincial faunas, by preventing exchange. Previously, it was thought that the Cretaceous world was biogeographically separated, with the northern continents being dominated by tyrannosaurids, South America by abelisaurids, and Africa by carcharodontosaurids. The subfamily Carcharodontosaurinae, in which Giganotosaurus belongs, appears to have been restricted to the southern continent of Gondwana (formed by South America and Africa), where they were probably the apex (top) predators. The South American tribe Giganotosaurini may have been separated from their African relatives through vicariance, when Gondwana broke up during the Aptian–Albian ages of the Early Cretaceous. Paleobiology In 1999, the paleontologist Reese E. Barrick and the geologist William J. Showers found that the bones of Giganotosaurus and Tyrannosaurus had very similar oxygen isotope patterns, with similar heat distribution in the body. These thermoregulatory patterns indicate that these dinosaurs had a metabolism intermediate between that of mammals and reptiles, and were therefore homeothermic (with a stable core body-temperature, a type of "warm-bloodedness"). The metabolism of an Giganotosaurus would be comparable to that of a mammalian carnivore, and would have supported rapid growth. In 2001, the physicist Rudemar Ernesto Blanco and Mazzetta evaluated the cursorial (running) capability of Giganotosaurus. They rejected the hypothesis by James O. Farlow that the risk of injuries involved in such large animals falling while on