Austroraptor

The holotype, labeled MML-195, consisted of a fragmentary skeleton including parts of the skull, lower jaw, a few neck and torso vertebrae, some ribs, a humerus, and assorted bones from both legs. It is the largest dromaeosaur to be discovered in the Southern Hemisphere; Novas et al. estimated that Austroraptor measured 5 m (16 ft) in length from head to tail. Gregory S. Paul later estimated its length at 6 m (20 ft) and weight of 300 kg (660 lb). However, Thomas R. Holtz Jr. has suggested that its weight is comparable to a lion, around 91–227 kg (200.6–500.4 lb). The skull is low and elongated, much more so than that of other dromaeosaurs, and measures 80 cm (31 in). Austroraptor has conical, non-serrated teeth, which Novas et al. compared to those of spinosaurids, based on how the enamel of the surface of its teeth is fluted. Austroraptor shares a trait that is unique to it and to Adasaurus: the descending process of the lacrimal bones curves anteriorly to a large degree. Austroraptor has a bizarre morphology in its pedal phalanges, which are strangely disproportionate. Phalanx IV-2 is over twice the width of phalanx II-2, and nearly three times the expected width based on similarly sized members of its taxonomic family. This has suggested to some researchers that the holotype specimen is a paleontological chimera; however, there is no uncertainty about the affinity of the taxon, so a chimera hypothesis can not be assured.

Several of Austroraptor 's skull bones bear some resemblance to those of the smaller troodontids. The front limbs of Austroraptor were short for a dromaeosaur, with its humerus less than half the length of its femur. Among the Dromaeodauridae, only this genus, Tianyuraptor, Zhenyuanlong and Mahakala have similarly reduced forelimbs. The relative length of its arms has caused Austroraptor to be compared to another, more famous short-armed dinosaur, Tyrannosaurus, though there is no close relationship between the two taxa.