ИСТИНА

The braincase of elasmosaurid plesiosaurs is poorly known despite numerous relatively complete and well-studied skeletons. Thereby a new find of an elasmosaurid basicranium from the Rybushka Formation (mid- Campanian) of Saratov Region, Russia, is of great interest. The specimen, attributed to an elasmosaurid plesiosaur, possess an elongated plate-like median keel of the parasphenoid and the condyle demarcated from the rest of the basioccipital by a deep groove. The studied basicranium is characterized by a number of peculiar features: extremely anteroposteriorly elongated pituitary fossa, single anterior foramen for the internal carotid arteries, reduced clinoid process, and deep channel on the basioccipital process. These features indicate profound morphological changes of the brain and head vessels compared with the other known plesiosaurs. Because of its hidden position, the pituitary fossa is rarely described in amniotes. However, the foramen for the anterior exit of the internal (cerebral) carotid artery is paired in most described amniotes. In all hitherto known sauropterygians these foramina are widely spaced (e.g. Rieppel, 1994; Druckenmiller, 2002; Sato et al., 2011). The single anterior foramen for the internal (cerebral) carotid was recently described in a new aristonectine elasmosaurid Alexandronectes zealandiensis (Otero et al., 2016). This feature is a potential synapomorphy for derived elasmosaurids.