Terminonatator (meaning "last swimmer") is a genus of elasmosaurid plesiosaur from the Late Cretaceous of Saskatchewan, Canada.

It is known from a skull and partial skeleton from a young adult, found in the Campanian-age Bearpaw Formation near Notukeu Creek in Ponteix.

Terminonatator is based on RSM P2414.1, a skull and partially articulated incomplete skeleton found high in the Bearpaw Formation.

Unlike other plesiosaurs, the pineal foramen in the roof of the skull was closed, and there were only nine teeth in the premaxillary bones that form the tip of the snout instead of ten, although this could be individual variation.

[1] Terminonatator is significant because of its late age, its inclusion of a skull with most of a skeleton, and its nature as an elasmosaurid (the remains of short-necked plesiosaurs are more common in comparable rocks in Canada).