Goniatite

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.

Morphology

All goniatites possessed an external shell, which is divided internally into chambers filled with gas giving it Buoyancy during the life of the animal. An open chamber at the front of the shell provided living space for the goniatitid animal, with access to open water through an aperture. The general morphology and habit of goniatites was probably similar to that of their later relatives the ammonites, being free swimming and possessing a head with two well developed eyes and arms (or tentacles).

Goniatite shells are small to medium in size, almost always less than 15 centimeters (5.9 inches) in diameter and often smaller than 5 centimeters (2.0 inches) in diameter. The shell is always planispirally coiled, unlike those of Mesozoic ammonites in which some are trochoidal and even aberrant (called heteromorphs). Goniatitid shells vary in form from thinly discoidal to broadly globular and may be smooth or distinctly ornamented. Their shape suggests many were poor swimmers