On the First Reliable Record of the Ichthyosaur Ophthalmosaurus icenicus Seeley in the Oxfordian–Kimmeridgian Beds of European Russia

Аннотация

An incomplete skeleton of the ichthyosaur Ophthalmosaurus icenicus Seeley, 1874 excavated in the Oxfordian–Kimmeridgian beds south of the town of Syzran (Samara Region) is described. Members of the genus Ophthalmosaurus are characterized by a unique combination of characters, most of which are well-pronounced in the specimen described here: the extracondylar area of the basioccipital is reduced, but still visible beyond the occipital condyle and has a well-pronounced ventral notch; the scapular shaft is mediolaterelly flattened; the humerus has three distal facets: the anterior facet is the smallest; the facet for the accessory preaxial element has a sharpened anterior margin; the facet for the radius faces distally; the facet for the ulna faces posterodistally; the posterior margin of the ulna is concave and sharpened, involved in the perichondral ossification; the intermedium is rhomboid, with two distal facets equal in size for the second and third distal carpals; the epipodial and autopodial elements are round and thickened, loosely arranged in the fin. This specimen is the first reliable evidence of the presence of Ophthalmosaurus in the Oxfordian–Kimmeridgian of Russia. The previously described remains of a Kimmeridgian ichthyosaur referred to as O. undorensis Efimov, 1991 should be identified as Ophthalmosauridae indet.