The Aristonectidae is a taxonomic family of poorly known plesiosaurs from the Jurassic and Cretaceous periods. They are closely related to polycotylid plesiosaurs. The family is made up of Tatenectes, Kimmerosaurus, Aristonectes, and Kaiwhekea. This group was formerly known as the Cimoliasauridae, but since Cimoliasaurus is indeterminate and quite possibly elasmosaurid, this replacement name was erected. Tatenectes and Kimmerosaurus represent an earlier Oxfordian Jurassic radiation from Laurasia, while Aristonectes and Kaiwhekea represent a later Cretaceous radiation from Gondwana.

Appearance

Aristonectidae were characterized by a relatively larger head and shorter neck than the Plesiosauridae and Elasmosauridae. Teeth resemble those of the Plesiosauridae. The group is known only from scanty and fragmentary remains. The formal diagnosis of the clade is that they possess: