Dinosaur Wiki


Early Cretaceous


Piscivore and molluscivore?






A. nataliae

Abyssosaurus nataliae is an extinct species of cryptoclidid plesiosaur known from the Early Cretaceous of Chuvash Republic, western Russia. Originally considered an elasmosaurid, phylogenetic analyses subsequently found it to nest with Colymbosaurus within the cryptoclydid subfamily Colymbosaurinae.

Abyssosaurus was originally known from a single specimen, but cranial remains were described in 2019. Abyssosaurus possessed an unusually short, triangular skull. The maxilla possesses features similar to those present in young elasmosaurids, and the enlarged eye sockets are another juvenile trait. Alexander Berezin has noted a number of neotenous/paedomorphic characteristics present in both the cranial and postcranial skeleton of Abyssosaurus. Given examples are the hypertrophy of the occipital bone, weak differentiation of cervical vertebrae, wide chest with thickened gastralia, and wide shoulders. The pachyostosis of the gastralia and flippers would have reduced its buoyancy. Additionally, Abyssosaurus is speculated to have possessed a retia mirabilia (“wonderful net”) of capillaries, like that present in cetaceans. The retia mirabilia would have been responsible for aiding the flow of blood to adipose tissue. In sperm whales, the retia mirabilia is particularly prominent, so Abyssosaurus was likely the same. In sum, there are a multitude of adaptations strongly implying that A. nataliae frequented deep-sea environments and frequently dove deep to obtain food.

The generic name of Abyssosaurus is derived from "abyss," and the Greek "sauros," meaning "lizard". Its specific epithet is in honour of Nataliya Berezina, the author's wife and research associate.

Regarding the paleobiology and paleoecology of Abyssosaurus, Berezin suggested that it fed by hovering diagonally above the seabed, in a manner akin to sperm whales. The reduced buoyancy required for such a lifestyle would explain the marked pachyostosis of the gastralia and flippers. That A. nataliae's expanded occipital surface suggests the presence of a retia mirabilia further lends credence to this notion. It is probable that Abyssosaurus dwelled and fed primarily in the bathypelagic zone, which was likely already rich in food sources by the time A. nataliae arose.

Initially, it was suggested that Abyssosaurus was intermediate between Tatenectes and Kimmerosaurus, two cryptoclidids, and Aristonectes and Kaiwhekea, two elasmosaurids. A phylogeny by Patrick Druckenmiller and Roger Benson, however, found it to be a cryptoclidid sister to Colymbosaurus, and thus an aberrant member of the Colymbosaurinae.