What is "polycotylidae"

Polycotylidae is a family of plesiosaurs from the Cretaceous, a sister group to Leptocleididae.

With their short necks and large elongated heads, they resemble the pliosaurs, but closer phylogenetic studies indicate that they share many common features with the Plesiosauridae and Elasmosauridae. They have been found worldwide, with specimens reported from New Zealand, Australia, Japan, Morocco, the USA, Canada, the former states of the USSR and South America.