Onychodus (/ɒˈnɪkədəs/, from Greek meaning "claw-tooth")[1] is a genus of prehistoric lobe-finned fish which lived during the Devonian Period (Eifelian - Famennian stages, around 374 to 397 million years ago).

The most well-preserved specimen of Onychodus has been found in the Gogo Formation of Western Australia giving palaeontologists more information about the structure of the fish.

On the sides of the body, Onychodus had a series of pores which provided a sensory system that enabled the fish to locate prey and to position itself in narrow spaces.

Long refer to a close phylogenetic relationship between Onychodus and the basal lobe-finned fish Psarolepis from China.

[3] In 1995, Roy Wagner,[4] Operations Manager for American Aggregates Corp., in Ostrander, Delaware County, Ohio, United States, found parts of Onychodus sigmoides including a lower jaw, and skull and other fragments.

All remains were found as isolated elements because the bones of Onychodus were loosely joined and dispersed quickly after the death of the fish.

[4] Studies show that Onychodus sigmoides was about 3 m in length and was the largest known bony fish of the Middle Devonian Period.

[6] O. yassensis was found in New South Wales at the Late Devonian Canowindra site and described by palaeontologist David Lindley in 2002.

[14] Onychodus jandemarrai, found in the Gogo Formation (Devonian) at Kimberley, Western Australia, is the best known species of the genus.

[19] This unusual characteristic was due to the loose attachment of the skull bones, which sometimes overlapped, and were connected only by soft tissue and cartilage.

The lower jaw was entirely articulated with cartilage, without an intermediate structure between the opposite sides, allowing the separation of the bones when prey was struck.

It is suggested that a ligament attachment and retractor mechanism existed in a pit under the tusk whorl, a unique condition in vertebrates.

[4] A fossil specimen of Onychodus from Western Australia was found with a placoderm fish half its length logged in its throat.

[4][19][21] The pectoral fins were strong enough for the animal to "walk" around the sea floor in search of a hiding place between coral colonies.