Tarachomylax: A new early Devonian dipnoan from Severnaya Zemlya, and its place in the evolution of the Dipnoi

The structure and significance of a new dipnoan genus and species, Tarachomylax oepiki, from the Emsian of Severnaya Zemlya (Siberian Arctic) is discussed. Many features of the genus are well displayed, but the external bones of the mandible and much of the cheek remain unknown. The new genus demonstrates that by Emsian times, features in advance of those shown by Speonesydrion, the best known of the Emsian tooth-plated genera, had evolved; these included tooth plates without a bulbous heel; long rows of teeth extending to the heel; and contact between bones B and A. None of these has been known previously in genera older than the Middle Devonian Dipterus. This indicates rapid evolution of tooth-plated Dipnoi shortly after their inception in the Pragian. The occurrence of Tarachomylax in marine rocks is yet another confirmation that this evolution took place in a marine environment.