Trilobites are extinct marine arthropods that form the class Trilobita. Trilobites form one of the earliest known groups of arthropods. The first appearance of trilobites in the fossil record defines the base of the Atdabanian stage of the Early Cambrian period and they flourished throughout the lower Paleozoic before slipping into a long decline, when, during the Devonian, all trilobite orders except the Proetida died out. The last trilobites disappeared in the mass extinction at the end of the Permian about 251.9 million years ago. Trilobites were among the most successful of all early animals, existing in oceans for almost 270 million years, with over 22,000 species having been described.
Proetida is an order of trilobite that lived from the Ordovician to the Permian. It was the last surviving order of trilobite, dying out in the Permian-Triassic extinction event.
Cephalaeschna is a genus of dragonflies in the family Aeshnidae.
Proetidae is a family of proetid trilobites. The first species appeared in the Upper Ordovician, and the last genera survived until the Middle Permian. However, if the closely related family Phillipsiidae is actually a subfamily of Proetidae, then the proetids of Proetidae survive until the end of the Permian, where the last perish during the Permian–Triassic extinction event.
Phillipsiidae is a family of proetid trilobites, the various genera of which comprise some of the last of the trilobites, with a range that extended from the Kinderhookian epoch of the Lower Mississippian, to the end of Changhsingian age at Permian-Triassic extinction event in the latest Permian period.
Proetoidea is a superfamily of trilobites in the order Proetida.
