Megaraptora is a clade of carnivorous tetanuran theropod dinosaurs with controversial relations to other theropods. Its derived members, the Megaraptoridae are noted for their elongated hand claws and proportionally large arms, which are usually reduced in size in other large theropods.
Megaraptorans are incompletely known, and no complete megaraptoran skeleton has been found. However, they still possessed a number of unique features. Their forelimbs were large and strongly built, and the ulna bone had a unique shape in members of the family Megaraptoridae, a subset of megaraptorans which excludes Fukuiraptor and Phuwiangvenator. The first two fingers were elongated, with massive curved claws, while the third finger was small.[7] Megaraptoran skull material is very incomplete, but a juvenile Megaraptor described in 2014 preserved a portion of the snout, which was long and slender.[8] Leg bones referred to megaraptorans were also quite slender and similar to those of coelurosaurs adapted for running.[7] Although megaraptorans were thick-bodied theropods, their bones were heavily pneumatized, or filled with air pockets. The vertebrae, ribs, and the ilium bone of the hip were pneumatized to an extent which was very rare among theropods, only seen elsewhere in taxa such as Neovenator.[9] Other characteristic features include opisthocoelous neck vertebrae and compsognathid-like teeth.[7]
The clade was originally named in 2010 as a subset of the family Neovenatoridae, a group of lightly-built allosauroids related to the massive carcharodontosaurids such as Giganotosaurus and Carcharodontosaurus.[9] A 2013 phylogenetic analysis by Fernando Novas and his colleagues disagreed with this classification scheme, and instead argued that the megaraptorans evolved deep within Tyrannosauroidea, a superfamily of basal coelurosaurs including the famous Tyrannosaurus.[7] Subsequent refinements to Novas's data and methodologies have supported a third position for the group, at the base of Coelurosauria among other controversial theropods such as Gualicho, but not within the Tyrannosauroidea.[10] Regardless of their position, it is clear that megaraptorans experienced a large amount of convergent evolution with either Neovenator-like allosauroids or basal coelurosaurs.[9][7]
Megaraptorans were most diverse in the early Late Cretaceous period of South America, particularly Patagonia. However, they had a widespread distribution. Phuwiangvenator and Fukuiraptor, the most basal and second most basal known members of the group, lived in Thailand and Japan, respectively. Megaraptoran material is also common in Australia,[11] and the largest known predatory dinosaur from the continent, Australovenator, was a megaraptoran.[12]
Megaraptorans were medium to large-sized theropods, ranging from Fukuiraptor, which was about 4.2 meters (13.8 feet) in length, to the 9 meter (30 feet) long Aerosteon, the 9 to 10 meter (30 to 33 feet) long Maip and the 12.8 meter (42 foot) long Bahariasaurus, if it is a member.[2] Most megaraptorans are known from very fragmentary remains, although certain characteristics can be identified in multiple members of the clade. At least some megaraptorans, such as Murusraptor and Aerosteon, had extensively pneumatic bones (most noticeably the ilia and ribs), which likely housed sinuses connected to the lungs, similar to modern birds.[13] The slender leg bones and long metatarsals of several species indicate that members of this group likely had cursorial habits.[9] Most megaraptorans are part of the family Megaraptoridae, which was named by Fernando Novas and his colleagues in 2013. This family is united by several adaptations of the ulna and claws which are not present in the basal megaraptoran Fukuiraptor.[7]