First sauropod dinosaur remains from the Early Cretaceous Shestakovo 3 locality, Western Siberia, Russia

Abstract

KOKM A, the associated caudal vertebrae of a sauropod from the Lower Cretaceous (Aptian) Ilek Formation at Shestakovo 3 locality in Kemerovo–Kuzbass oblast, Western Siberia, Russia, shows a unique combination of derived caudal vertebrae and plesiomorphic and highly diverse haemal arches (chevrons). The anterior, middle, and posterior caudal vertebrae are deeply procoelous with a ball-like posterior condyle. There are five type of chevrons: closed Y-shaped anterior chevrons with a small haemal canal, closed asymmetric middle chevrons with a small ventral slit, open forked middle chevrons with large ventral slit, separate posterior chevrons with chevron facets, and separate posterior rodlike chevrons without chevron facets. The equal weight and extended implied weighting parsimony analyses place KOKM A within Turiasauria and Titanosauria, respectively. Both these analyses place Sibirotitan astrosacralis from the nearby Shestakovo 1 locality of the same stratigraphic unit in Mamenchisauridae. Both equal weight and extended implied weighting analyses combining S. astrosacralis and KOKM A in a single terminal taxon place it as a non-lithostrotian titanosaur, in particular, as a sister taxon for Daxiatitan binglingi from the Lower Cretaceous of China. D. binglingi is similar to S. astrosacralis and KOKM A in structure of cervical and caudal vertebrae, respectively. This suggests attribution of KOKM A to S. astrosacralis.