A Sauropod Fibula (Dinosauria, Sauropoda) from the Lower Cretaceous of the Kuzbass Region, Russia

A proximal fragment of a fibula from the Lower Cretaceous Shestakovo 3 locality in the Kemerovo Region—Kuzbass can be attributed to a medium-sized sauropod with an estimated body length of approximately 16 m. Its histological features—a poorly vascularized primary cortex with an external fundamental system and a Haversian bone in the deeper cortical layers—indicate that this fibula belonged to an adult individual that had reached its maximum size. The presence of an anteromedial ridge at the proximal end, the shape of the proximal epiphysis, the sigmoidal curvature of the bone in anterior or posterior view, and the weak development of the lateral trochanter, support the confident assignment of this specimen to the family Euhelopodidae. A previously described series of procoelous caudal vertebrae from the Shestakovo 3 locality belongs to a representative of the clade Titanosauria, indicating the coexistence of two sauropod taxa—Euhelopodidae indet. and Titanosauria indet.—at this locality.