Ischnacanthiformes

Ischnacanthiformes is an extinct order of acanthodian fish that lived during the Devonian period. Acanthodians are an early group of jawed vertebrates, often referred to as "spiny sharks" due to their distinctive fin spines. The Ischnacanthiformes are characterized by their dentition, which typically featured numerous small, sharp teeth on the jaws. These teeth were not replaced throughout the fish's life; instead, they were continuously shed and regrown. This unique dental replacement pattern is a key diagnostic feature of the order.

Fossils of Ischnacanthiformes are found primarily in marine and sometimes brackish water deposits. They were likely predatory or scavenging fish, with their teeth adapted for grasping or tearing small prey. The skeletal remains of Ischnacanthiformes are often fragmented, with isolated teeth and spines being common finds. Understanding their anatomy and relationships relies heavily on these fossil fragments. The group is considered to have been widespread during the Devonian, before eventually going extinct, contributing to the broader picture of early vertebrate evolution.