Holocephali

Holocephali Temporal range: 416–present Devonian–present
Hydrolagus colliei, a rat fish
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Chondrichthyes
Subclass:	Holocephali
Orders
Chimaeriformes †Petalodontiformes †Iniopterygiformes †Eugeneodontida †Symmoriida[1]

Holocephali ("complete heads") is a subclass of cartilaginous fish, of which the order Chimaeriformes is the only surviving group.

Holocephali have a long fossil record that starts during the Devonian period. However, most fossils are teeth, and the body forms of numerous species are not known, or, at best, poorly understood. Sequence analysis on living chimaera suggests the whole group originated 420 million years ago in the Silurian period.^[2]

1. ↑ Coates, M., Gess, R., Finarelli, J., Criswell, K., Tietjen, K. 2016. A symmoriiform chondrichthyan braincase and the origin of chimaeroid fishes. Nature. doi:10.1038/nature20806
2. ↑ Inoue J.G. et al 2010. Evolutionary origin and phylogeny of the modern holocephalans (Chondrichthyes: Chimaeriformes): a mitogenomic perspective. Molecular Biology and Evolution. 27 (11): 2576-2586.