Goniatites are an extinct group of marine cephalopods related to ammonites that form the order Goniatitida. Goniatites appeared during the Middle Devonian, about 400 million years ago, and became extinct at the end of the Permian, about 250 million years ago.
Goniatites had an external shell divided into gas-filled chambers that provided buoyancy. An open chamber at the front of the shell housed the animal, with access to the water through a ventral opening. Their general morphology and lifestyle were probably similar to those of their later relatives, the ammonites. They could swim freely and had a head with two eyes and well-developed arms or tentacles.
The typical goniatite has a specific suture on its shell, which gives it the name "goniatite." On some, the sutures feature a distinctive "zigzag" pattern.
Goniatites are found in North America, Europe, North Africa, and Australasia, where they are used as index fossils for age determination and stratigraphic correlation. Notable concentrations of goniatites are found in certain limestones in western Ireland (especially Slieve Anierin), which are packed with beautifully preserved goniatite fossils. They are also found in the marine bands of Carboniferous coal in Europe and in marine rocks from the Pennsylvanian period in Arkansas. Large numbers of goniatites are also found in rocks from the Devonian period in Morocco.
Fossilised goniatite shell showing its characteristic suture – Wikipedia
