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.

Euryapsida