Mapusaurus

Mapusaurus (Earth Lizard) was a giant carnosaurian dinosaur from the Middle-Late Cretaceous of what is now Argentina. It was similar in size to its close relative Giganotosaurus, with the largest known individuals estimated as 41 feet (12.6 meters) in length and weighing approximately 6 tons. Mapusaurus was excavated between 1997 and 2001, by the Argentinian-Canadian Dinosaur Project, from an exposure of the Huincul Formation at Canadon de Gato. It was described and named by paleontologists Rodolfo Coria and Phil Currie in 2006. The name Mapusaurus means "Earth Lizard. The type species, Mapusaurus roseae, is named for both the rose-colored rocks, in which the fossils were found and for Gorden Letwin, who sponsored the expeditions which recovered these fossils.

Classification
Cladistic analysis carried out by Coria and Currie definitively showed that Mapusaurus is nested within the Carcharodontosauridae family. The authors noted that the structure of the femur suggests a closer relationship with Giganotosaurus than either taxon shares with Carcharodontosaurus. They created a new monophyletic taxon based on this relationship, the subfamily Giganotosaurinae, defined as all carcharodontosaurids closer to Giganotosaurus and Mapusaurus than to Carcharodontosaurus. They tentatively included the genus Tyrannotitan in this new subfamily, pending publication of more detailed descriptions of the known specimens of that form.

Paleobiology
The fossil remains of Mapusaurus were discovered in a bone bed containing at least seven individuals of various growth stages. Coria and Currie speculated that this may represent a long term, possibly coincidental accumulation of carcasses (some sort of predator trap) and may provide clues about Mapusaurus behavior. Other known theropod bone beds include the Allosaurus-dominated Cleveland Lloyd Dinosaur Quarry of Utah, an Albertosaurus bone bed from Alberta and a Daspletosaurus bone bed from Montana. Paleontologist Rodolfo Coria, of the Museo Carmen Funes, contrary to his published article, repeated in a press-conference earlier suggestions that this congregation of fossil bones may indicate that Mapusaurus hunted in groups and worked together to take down large prey, such as the immense sauropod Argentinosaurus. If so, this would be the first substantive evidence of gregarious behavior by large theropods other than Tyrannosaurus, although whether they might have hunted in organized packs (as wolves do) or simply attacked in a mob, is unknown. The authors interpreted the depositional environment of the Huincul Formation at the Canadon de Gato locality as a freshwater paleochannel deposit, "laid down by an ephemeral or seasonal stream in a region with arid or semi-arid climate". This bone bed is especially interesting, in light of the overall scarcity of fossilized bone within the Huincul Formation.