Euryapsida (Synaptosauria; class Reptilia) A subclass of reptiles that have a single, upper temporal opening behind the eye. The subclass includes the Plesiosauroidea, Nothosauria, and Placodontidae. The Ichthyosauria had a similarly placed opening but there were key differences in the arrangement of the bones forming its margins. For this and other reasons the ichthyosaurs are placed in the subclass Ichthyopterygia. Euryapsids were typically aquatic especially from the mid-Triassic onwards. They first appeared in the Permian and became extinct at the end of the Mesozoic.

Euryapsida Reptiles which have a single, upper temporal opening behind the eye. The group includes the plesiosaurs, nothosaurs, and the placodonts. The ichthyosaurs had a similarly placed opening, but there were key differences in the arrangement of the bones forming its margins: for this and other reasons, the ichthyosaurs are usually placed in a different subclass from the euryapsids, the Ichthyopterygia. However, like the ichthyosaurs, the euryapsids were typically aquatic types, especially from the mid-Triassic onwards. Euryapsids first appeared in the Permian and became extinct at the end of the Mesozoic.