Echinoderms: One half billion years of survival.

The phylum Echinodermata survived the five major prehistoric extinction events. Although many died off, other echinoderms survived the late Ordovician mass extinction 443 million years ago that killed most of the trilobites. Echinoderms survived the Kellwasser event 372 million years ago, the Great Dying known as the the End-Permian extinction event 252 million years ago, the end-Triassic extinction 201 million years ago, the Cretaceous–Tertiary (K–T) extinction that killed the dinosaurs 66 million years ago, and the Eltanin of 2.51 million years ago. Echinoderms are exclusively marine and found in the full depth range from scuba divable waters to deep trenches. As well, they are found from the tropics to the polar regions.