Mapusaurus
Mapusaurus (meaning "Earth lizard") was a giant carcharodontosaurid carnosaurian dinosaur from the early Late Cretaceous (late Cenomanian to early Turonian stage), approximately 97 to 93 million years ago, of what is now Argentina. Discovery. "Mapusaurus" was excavated between 1997 and 2001, by the Argentinian-Canadian Dinosaur Project, from an exposure of the Huincul Formation (Rio Limay Subgroup, Cenomanian) at Cañadón del Gato. It was described and named by paleontologists Rodolfo Coria and Phil Currie in 2006. The name "Mapusaurus" is derived from the Mapuche word "Mapu", meaning 'of the Land' or 'of the Earth' and the Greek "sauros", meaning  'lizard'. The type species, "Mapusaurus roseae", is named for both the rose-colored rocks, in which the fossils were found and for Rose Letwin, who sponsored the expeditions which recovered these fossils. The designated holotype for the genus and type species, "Mapusaurus roseae", is an isolated right nasal (MCF-PVPH-108.1, Museo Carmen Funes, Paleontología de Vertebrados, Plaza Huincul, Neuquén). Twelve paratypes have been designated, based on additional isolated skeletal elements. Taken together, the many individual elements recovered from the "Mapusaurus" bone bed represent most of the skeleton. Description. "Mapusaurus" was a large theropod, and was roughly similar in size to  its close relative "Giganotosaurus", with the largest known individuals estimated as about to in length or more and weighing about to . The longest individual for which Coria and Currie (2006) provided a concrete estimate in Table 1 (appendix lll) is the animal to which femur MCF-PVPH-208.203 belonged; this individual is estimated as long. Coria and Currie note the presence of isolated bones from at least one longer individual, but do not provide a figure, instead finding the larger bones coherent with an individual of comparable size to "Giganotosaurus" holotype estimated at in length, although not with the same exact  proportions, having taller and wider neural spines, a more elongate fibula ( compared to ) but more slender (81–89% the width as in "Giganotosaurus") as well as a wider pubic shaft in minimal dimensions (10% wider as indicated by a long fragment catalogued as MCF-PVPH-108.145), and with a differently proportioned skull, shorter in length than "Giganotosaurus" because the maxilla is not elongated (12 teeth compared to 14 in "Carcharodontosaurus"), but deeper in proportion due to this, as well as narrower (due to the narrow nasals). Considering this, a fragmentary maxilla is coherent with the size of the "Giganotosaurus"-sized individual (MCF-PVPH-108.169 ). A neural arch from an axis (MCF-PVPH-108.83) and a scapular blade fragment are also the same exact size as the same elements in "Giganotosaurus". The weight estimate of is from a long femur with a circumference (MCF-PVPH-208.234). Holtz estimated the maximum size of the animal at . This estimate has been cited in Drew Eddy and Julia Clarke (2011), and cited again in a phylogenetic table in a 2014 analysis by Canale "et al.". Gregory Paul gave a lower estimation of 11.5 meters (37.7 ft) and 5 metric tons (5.5 short tons). It has been determined that "Mapusaurus" was  diagnosed on autapomorphies, or unique traits, in regions of the skeleton that "Giganotosaurus" does not preserve. "Mapusaurus" only differs from "Giganotosaurus" in lacking a second opening on the middle quadrate, and in some details of the topology of the nasal rugosities. 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" like "Giganotosaurus" also 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 Cañadón del 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. An ontogenetic study by Canale "et al." (2014) found that "Mapusaurus" displayed heterochrony, an evolutionary condition in which the animals may retain an ancestral characteristic during one stage of their life, but lose it as they develop. In  Mapusaurus, the maxillary fenestrae are present in younger individuals, but gradually disappear as they mature. Classification. Cladistic analysis carried out by Coria and Currie definitively showed that "Mapusaurus" is nested within the clade Carcharodontosauridae. 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. The following cladogram after Novas "et al.", 2013, shows the placement of "Mapusaurus" within Carcharodontosauridae. Paleoecology. As previously mentioned, the Huincul Formation is thought to represent an arid environment with ephemeral or seasonal streams. The age of this formation is estimated at 97 to 93.5 Mya. The dinosaur record is considered sparse here. "Mapusaurus" shared its environment with the sauropods "Argentinosaurus" (one of the largest sauropods, if not the largest), "Choconsaurus", and "Cathartesaura". Abelisaurid theropods "Skorpiovenator" and "Ilokelesia" also lived in the region. Fossilized pollen indicates a wide variety of plants was present in the Huincul Formation . A study of the El Zampal section of the formation found hornworts, liverworts, ferns, Selaginellales, possible Noeggerathiales, gymnosperms (including gnetophytes and conifers), and angiosperms (flowering plants), in addition to several pollen grains of unknown affinities. The Huincul Formation is among the richest Patagonian vertebrate associations, preserving fish including dipnoans and gar, chelid turtles, squamates, sphenodonts, neosuchian crocodilians, and a wide variety of dinosaurs. Vertebrates are most commonly found in the lower, and therefore older, part of the formation.