Monotypic prehistoric fish genera

Tiktaalik (; ) is a monospecific genus of extinct sarcopterygian (lobe-finned fish) from the late Devonian Period, about 375 Mya (million years ago), having many features similar to those of tetrapods (four-legged animals). Tiktaalik is estimated to have had a total length of on the basis of various specimens.

Jamoytius kerwoodi is an extinct species of primitive, eel-like jawless fish known from the Patrick Burn Formation in Scotland, dating to the Llandovery epoch of the Early Silurian period.

Pholidophorus (from , 'horny scale' and , 'to bear') is an extinct genus of stem-teleost fish. Numerous species were assigned to this genus in the past, but only the type species Pholidophorus latiusculus, from the Late Triassic of Europe, is considered to be a valid member of the genus today.

Janusiscus schultzei is an extinct gnathostome vertebrate dating from the Early Devonian period in Siberia, approximately 415 million years ago. It may be the sister group of the last common ancestor of Chondrichthyes (cartilaginous fish) or Osteichthyes (bony fish). This makes J. schultzei a sister species to all living jawed vertebrates. The species name is in honor of Hans-Peter Schultze; the genus named after Janus, the Roman god of duality.