Both cidaroids and the ancestors to the euechinoids passed from the Palaeozoic into the Mesozoic, but we know very little about this period in the group's history. In the Triassic both cidaroids and ...

This is a synapomorphy for the crown group of the Echinoidea, and is also true for all post-Palaeozoic echinoids, bar one, Tiarechinus. By contrast almost all Palaeozoic echinoids have a test which ...