Onychodus was about 2 to 4 meters in length and was a pelagic animal.[5] Like other onychodontiformes, it had a pair of tooth spirals (parasymphysial tooth whorls) bearing tusk-like teeth. The most well-preserved specimen of Onychodus has been found at the Gogo Formation of Western Australia giving palaeontologists more information about the structure of the fish. Other species of Onychodus are known only from poor material based on isolated tusks, teeth and scales.