Holocephali

Holocephali (sometimes spelled Holocephala; Greek for "complete head" in reference to the fusion of upper jaw with the skull) is a subclass of cartilaginous fish. The only living holocephalans are the three families of chimaeras, but the group also includes many extinct members and was more diverse during the Paleozoic and Mesozoic eras. The earliest known fossils of holocephalans date to the Middle Devonian, and the subclass likely reached its peak diversity during the following Carboniferous Period. Molecular clock studies suggest that holocephalans diverged from their closest relatives, ela

REDIRECT Chondrenchelyiformes

Orodontiformes is an extinct group of cartilaginous fish, known from the Late Devonian and Carboniferous periods. They are part of Euchondrocephali (Holocephali sensu lato), making their closest living relatives chimaeras. Most members are only known from teeth, which are low and rounded, and designed for crushing prey (durophagy). The group in its totality has been described as "undoubtedly artificial" (i.e. non-monophyletic). Several species of Orodus are known from specimens preserving the body as well as the teeth.

left|thumb|Life reconstruction of Deltoptychius alongside the related Menaspiformes|menaspiform [[Menaspis]] Deltoptychius (from , 'triangle' and 'fold') is an extinct species of cartilaginous fish related to the modern chimaeras. It lived in the Carboniferous period in present-day United Kingdom. Fossils of the genus have been found in the Glencartholm Volcanic Beds Formation of the Upper Border Group in Scotland.

Cochliodontiformes are an order of extinct holocephalans (historically referred to as bradyodonts) known from the Devonian, Carboniferous and Permian periods. Members of the order are believed to be durophagous benthic carnivores.