Goniatids, informally Goniatites, are ammonoid cephalopods that form the Order Goniatiida, derived from the more primitive Anarcestida during the Middle Devonian some 390 million years ago. Goniatites (goniatitida) survived the Late Devonian extinction to flourish during the Carboniferous and Permian only to become extinct at the end of the Permian some 139 million years later. 1 1/2 to 2 inches across