What does the plesiosaur family tree look like?
There are two major groups of plesiosaurs: one group had the classic small head on a long, serpentine neck. This is the plesiosaurs proper. From the plesiosaurs evolved a family known as the cryptocleidids. The other group had large heads on short necks. This is the pliosaur family. It appeared later than the plesiosaur family in the Early Jurassic. A family of extra-large plesiosaurs, the elasmosaurs with spectacularly long necks, appeared in the Cretaceous.
