Holocephala

Holocephali (Sometimes spelled Holocephala; Greek for "complete head" in reference to the fusion of upper jaw with the rest of the skull) is a subclass of mostly extinct cartilaginous fish. While Holocephali is today represented by three families and a single order which together are commonly known as chimaeras, the group was far more diverse throughout the Paleozoic and Mesozoic eras. The earliest known fossils of holocephalans date to the Middle Devonian period, and the group...