goniatites

Goniatites are an extinct group of marine mollusks belonging to the subclass Goniatitina. They are ammonoids, a type of cephalopod closely related to modern squid and nautiluses. Goniatites first appeared in the Devonian period, around 400 million years ago, and became particularly diverse and abundant during the Carboniferous and Permian periods. They went extinct at the end of the Permian period, approximately 252 million years ago, during the Permian-Triassic extinction event, the largest mass extinction in Earth's history.

These ancient creatures are characterized by their coiled shells, which were typically involute, meaning the later whorls completely covered the earlier ones. The most distinctive feature of goniatites, and what gives them their name, is the shape of their suture lines. Suture lines are the patterns formed where the internal walls (septa) of the shell chambers meet the shell itself. In goniatites, these suture lines are generally simple, typically exhibiting only one or two lobes and saddles. This contrasts with later ammonites, which developed much more complex and frilled suture patterns.

Fossilized goniatite shells are common in Paleozoic marine sedimentary rocks worldwide. Their presence and abundance in specific rock layers make them valuable index fossils, helping geologists to date and correlate rock formations. The study of goniatites has provided significant insights into the evolution of cephalopods and the paleoecology of ancient marine environments.