New data on the tyrannosauroid dinosaur Kileskus from the Middle Jurassic of Siberia, Russia

Abstract

ABSTRACT New postcranial bones (cervical and caudal vertebrae, chevron, fibula) of the proceratosaurid tyrannosauroid Kileskus aristotocus from the Middle Jurassic (Bathonian) Itat Formation at Berezovsk coal mine, Krasnoyarsk Territory, Western Siberia, Russia, reveal three possible autapomorphies of Kileskus: a deep anterior recess between the neural canal and prezygapophysis; a distinct pit at the base of the neural spine on the middle cervical vertebrae; and a ventral groove on the middle caudal vertebrae. Phylogenetic analysis recovered a nearly horizontal posterior centrodiapophyseal lamina in the anterior-middle cervicals with the infrapostzygapophyseal fossa located primarily dorsally to the lamina as a new synapomorphy for the Proceratosauridae. The deep oval fossa on the medial surface of the fibula with well-defined margins is a tyrannosauroid synapomorphy of Kileskus. In other Proceratosauridae the fibula is either absent or not described in detail. The longitudinal and reticular vascularization of the primary cortex in the Kileskus tibia suggests a slower growth rate compared with large-bodied tyrannosaurids.