Descriptions of Small Dinosaurs

Hesperonychus has not made much of a buzz since it was initially described. That paper, shared on Saturday initially but here again today (Longrich and Currie, 2009), includes the expected high detail photographs of the type material, but it also includes museum material hypothesized, but not necessarily known, to belong to Hesperonychus. The conclusions that caused this material, isolated pedal phalanges, to be referred to this species, was tentative at the time and has been based on characteristics of size and shape that place the toes in the same family and, because of the size, attribute them to an adult animal approximately the size of the estimated adult size of Hesperonychus. These phalanges are described and compared to the phalanges of other taxa in order to justify their reference to this species of dromaeosaur. Key elements of the pelvic girdle that mark the animal as an adult stand as diagnostic characters that separate Hesperonychus from other genera and the possibility of the small dromaeosaur belonging to another genera as a subadult or even as a juvenile. The characteristic growth described here is fusion of the pubes and ilia, a morphology seen in "somatically mature" animals, as Longrich and Currie state. A phylogenetic discussion is presented as well in an attempt to ascertain the precise clade to which Hesperonychus belongs and its position in both this specific and the larger dromaesaurine clade as well.