Giganotosaurus was one of, but not the greatest predatory dinosaur ever discovered, but it was large. It was found all over South America. It's name means "Giant Reptile of the South".

Giganotosaurus was found in 1993 near the town of El Chocon in Northern Patagonia, Argentina.

Giganotosaurus was discovered by Ruben Carolini, an amateur fossil hunter who, in 1993, discovered the fossils in deposits of Patagonia (southern Argentina) in what is now considered the Candeleros Formation. It was published by Rodolfo Coria and Leonardo Salgado in the journal Nature in 1995.

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.

The holotype specimen's (MUCPv-Ch1) skeleton was about 70% complete and included the skull, pelvis, leg bones and most of the backbone. Various estimates find that it measured somewhere between 12.2 and 12.5 m (40-41 ft) in length, and between 6.5 and 13.3 tons in weight. A second, more fragmentary, specimen (MUCPv-95) has also been recovered. It is only known from a portion 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 (6.3 ft), compared to the holotype's estimated at 1.80 m (6 ft) skull, making it likely that Giganotosaurus had the largest skull of any known theropod. Giganotosaurus surpassed Tyrannosaurus in mass by at least half a ton (the upper size estimate for T. rex is 9.1 t).

G. carolinii was slightly larger than T. rex, but had a brain only about half as big as those of tyrannosaurids. 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. A well-developed olfactory region means that it probably had a good sense of smell. Its skull, although large, had a slender build.

The original fossils of Giganotosaurus remain at the Carmen Funes Museum in Neuquen, Argentina, but replicas are common in other places, including the Australian Museum in Sydney. Despite having been discovered relatively recently, Giganotosaurus is already gaining a name for itself in popular culture. Giganotosaurus was featured in Dino Crisis 2, but was somewhat exaggerated in size; the game's giganotosaur was said to be over 7 metres tall and 20 meters long, when the actual creature was about 5.5 metres tall and 14 meters long. It was capable of throwing an adult Tyrannosaurus. Giganotosaurus appears in the Chased by Dinosaurs special Land of Giants. They are seen to hunt both independently and in packs, working together to bring down an Argentinosaurus. Giganotosaurus is also featured in the IMAX movie Dinosaurs: Giants of Patagonia where Dr. Rodolfo Coria shows the sites of major discoveries in Argentina. It also has a robotic animal kit, from the popular Zoids series, released after the species known as Gojulas Giga. Giganotosaurs appear in the Dinotopia story The World Beneath as unexpected protagonists in the Rainy Basin. A Giganotosaurus made a brief appearance in the 2008 movie Journey to the Center of the Earth. Giganotosaurus also appeared in the third season of Primeval, where it was portrayed as being capable of running huge distances at high speeds despite its massive size and weight. It attacks a jumbo jet and kills wildlife expert Nigel Marven.