Editing Placoderm (section)

====Acanthothoraci====
[[File:Palaeacanthaspis vasta.jpg|thumb|upright|left|''[[Palaeacanthaspis]]'']]
[[Acanthothoraci]] ("spine chests") were a group of [[Chimaera|chimaera-like]] placoderms closely related to the rhenanid placoderms. Superficially, acanthoracids resembled scaly [[chimaera]]s or small, scaly arthrodires with blunt [[Rostrum (anatomy)|rostrums]]. They were distinguished from chimaeras by a pair of large spines that emanate from their chests, the presence of large scales and plates, tooth-like beak plates, and the typical bone-enhanced placoderm eyeball. They were distinguished from other placoderms due to differences in the anatomy of their skulls, and due to patterns on the skull plates and thoracic plates that are unique to this order. From what can be inferred from the mouthplates of fossil specimens, acanthothoracids were shellfish hunters ecologically similar to modern-day chimaeras. Competition with their relatives, the ptyctodont placoderms, may have been one of the main reasons for the acanthothoracids' extinction prior to the mid-Devonian extinction event.