Morphology of the earliest reconstructable tetrapod Parmastega aelidae

The taxonomic diversity of Devonian tetrapods has increased dramatically in recent decades, but much of this diversity consists of tantalising fragments. The interpretative framework for the earliest stages of tetrapod evolution is still dominated by the near-complete Ichthyostega and Acanthostega, with supporting roles for the less complete but partly reconstructable Ventastega and Tulerpeton. All four are of late Famennian age, 10 million years younger than the earliest tetrapod fragments and nearly 30 million years younger than the oldest footprints. Here we describe a tetrapod from the earliest Famennian of Russia, Parmastega aelidae gen. et sp. nov., represented by three-dimensional material that allows reconstruction of almost the entire skull and dermal shoulder girdle. Its raised orbits, lateral line canals and weakly ossified postcranial skeleton suggest a largely aquatic, surface-cruising animal. In Bayesian and parsimony-based phylogenetic analyses the majority of trees place Parmastega as sister group to all other tetrapods.