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, Tar achomylax 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 o f those shown by Speonesydrion, the best known of the Emsian tooth-pla ted genera, had evolved; these included tooth plates without a bulbous heel; long rows of teeth extending to the heel; and contact between b ones B and A. None of these has been known previously in genera older than the Middle Devonian Dipterus. This indicates rapid evolution of t ooth-plated Dipnoi shortly after their inception in the Pragian. The o ccurrence of Tarachomylax in marine rocks is yet another confirmation that this evolution took place in a marine environment.