Morphology of the Craniovertebral Joint in Psittacosaurus sibiricus (Ornithischia: Ceratopsia)

The joint of the occipital skull region and two first cervical vertebrae of Psittacosaurus sibiricus from the Shestakovo locality (Barremian–Aptian), Kemerovo Region, Russia is described. The morphological differences in the atlas–axis complex between the infraorders Psittacosauria and Neoceratopsia connected with their functional features are revealed. The atlas–axis complex of P. sibiricus consists of two unfused vertebrae. The atlas includes...