New Data on Sibirotitan, a Titanosauriform Sauropod from the Early Cretaceous of Western Siberia

The previously unknown second cervical vertebra (axis) of the sauropod Sibirotitan astrosacralis Averianov et al., 2018 from the Early Cretaceous locality Shestakovo 1 (Ilek Formation, Aptian) in Kemerovo oblast, Russia, makes it possible to supplement the morphological characterization of this dinosaur species. The described axis is characterized by unique features such as a flat and rectangular ventral surface of the vertebral centrum and dorsally ascending spinopostzygapophyseal laminae. A unique common feature of the axis and other cervical vertebrae of Sibirotitan is the presence of large and deep centropostzygapophyseal fossae on the posterior surface of the neural arch between the neural canal and the postzygapophyses. All these characters can be considered as autapomorphies of Sibirotitan astrosacralis .