of prey smaller than themselves, such as juvenile sauropods. The ventral process (or "chin") of the lower jaw may have been an adaptation for resisting tensile stress when the powerful bite was delivered with the front of the jaws against the prey. The first known fossils of the closely related Mapusaurus were found in a bonebed consisting of several individuals at different growth stages. In their 2006 description of the genus, Coria and Currie suggested that though this could be due to a long term or coincidental accumulation of carcasses, the presence of different growth stages of the same taxon indicated the aggregation was not coincidental. In a 2006 National Geographic article, Coria stated that the bonebed was probably the result of a catastrophic event and that the presence of mainly medium-sized individuals, with very few young or old, is normal for animals that form packs. Therefore, Coria said, large theropods may have hunted in groups, which would be advantageous when hunting gigantic sauropods. Paleoenvironment Giganotosaurus was discovered in the Candeleros Formation, which was deposited during the Early Cenomanian age of the Late Cretaceous period, approximately 99.6 to 97 million years ago. This formation is the lowest unit in the Neuquén Group, wherein it is part of the Río Limay Subgroup. The formation is composed of coarse and medium-grained sandstones deposited in a fluvial environment (associated with rivers and streams), and in aeolian conditions (effected by wind). Paleosols (buried soil), siltstones, and claystones are present, some of which represent swamp conditions. Giganotosaurus was probably the apex predator in its ecosystem. It shared its environment with herbivorous dinosaurs such as the titanosaurian sauropod Andesaurus, and the rebbachisaurid sauropods Limaysaurus and Nopcsaspondylus. Other theropods include the abelisaurid Ekrixinatosaurus, the dromaeosaurid Buitreraptor, and the alvarezsauroid Alnashetri. Other reptiles include the crocodyliform Araripesuchus, sphenodontians, snakes, and the turtle Prochelidella. Other vertebrates include cladotherian mammals, a pipoid frog, and ceratodontiform fishes. Footprints indicate the presence of large ornithopods and pterosaurs as well. References External links Canadian Museum of Nature: "Who was the ultimate dino? Giganotosaurus or T. rex?" – video presented by Jordan Mallon Carcharodontosaurids Cenomanian life Late Cretaceous dinosaurs of South America Cretaceous Argentina Fossils of Argentina Candeleros Formation Fossil taxa described in 1995 Apex predators Taxa named by Rodolfo Coria