A new basal coelurosaur (Dinosauria: Theropoda) from the Middle Jurassic of Siberia

Abstract

Kileskus aristotocus gen. et sp. nov. from the Middle Jurassic (Bathonian) Itat Formation at Berezovsk Quarry, Krasnoyarsk Territory (West Siberia, Russia), is based on an associated maxilla and premaxilla, a mandible fragment, and some possible associated postcranial elements. Kileskus gen. nov. is referred together with the Middle Jurassic Proceratosaurus from England and the Late Jurassic Guanlong from China to Proceratosauridae fam. nov. (Tyrannosauroidea, Coelurosauria) which is characterized by sagittal nasal crest (unknown for Kileskus gen. nov.), enlarged external nares, short ventral margin of premaxilla, and depth of the antorbital fossa ventral to the antorbital fenestra that is much greater than the depth of the maxilla below the ventral margin of the antorbital fossa. Kileskus gen. nov. is more similar to Proceratosaurus than to Guanlong in having anterodorsal process of the premaxilla inclined slightly anterodorsally and nares inclined posterodorsally, but differs from these two genera by having ascending process of the maxilla confluent with anterior rim of maxillary body and gently sloping posterodorsally. Kileskus gen. nov. has a basal position within the Proceratosauridae. Dilong from the Early Cretaceous of China with a parasagittal nasal crests is the sister taxon for the Proceratosauridae. The new taxon is one of the oldest members of Coelurosauria and Tyrannosauroidea in the fossil record.