Abstract

A partial ornithomimid skeleton, ROM 1790, from the lower Dinosaur Park
Formation (upper Campanian) of Alberta was previously referred to Struthiomimus
altus, but lacks diagnostic characters of that species. It is described as the holotype
of a new species, Rativates evadens gen. et sp. nov., diagnosed by the form of the
maxilla-jugal contact, the reduction of the mid-caudal neural spines, the convex
fusion of the left and right ischia, the relatively enlarged medial condyle of the tibia,
and the straight-edged distal end of the third metatarsal. A histological section of the
femur confirms that the type specimen is not a juvenile, despite its relatively small
size (approximately 50% as massive as large individuals of Struthiomimus altus).
Phylogenetic analysis recovers Rativates as a member of a derived ornithomimid
clade that includes Ornithomimus, Struthiomimus, and the Asian taxa Anserimimus
and Qiupalong. Fusion of the proximal tarsals to the tibia in some ornithomimid
specimens was observed to be more complete than previously recognized,
increasing the known resemblance of these non-avian coelurosaurs to birds.