Revision of the trematosaurid <i>Erythrobatrachus noonkanbahensis</i> confirms a cryptic marine temnospondyl community from the Lower Triassic of Western Australia

Tetrapods emerged as dominant marine predators during the earliest Triassic, with trematosaurid temnospondyls representing one of the first groups to radiate globally after the cataclysmic end-Permian mass extinction. Trematosaurids were superficially ‘crocodile-like’ amphibians with elongate tapered skulls and dorsolaterally oriented orbits that suggest adaptation for living within the water column. In Australia, marine trematosaurid fossils have only been recovered from the Blina Shale—an upper Induan–lower Olenekian paralic unit that crops out in the Canning Basin of remote northwestern Western Australia. The Blina Shale was deposited along the edge of a brackish seaway that inundated the East Gondwana interior rift-sag system separating what is today the Australian and Indian landmasses. Historically, a single trematosaurid species, Erythrobatrachus noonkanbahensis, was described from the Blina Shale. However, recent survey of the remains reveals a morphological composite combining the broad-skulled holotype of E. noonkanbahensis, with an extremely narrow-skulled referred specimen that closely resembles the cosmopolitan lonchorhynchine genus Aphaneramma. The Blina Shale temnospondyl assemblage therefore integrated multiple marine trematosaurids that were locally, and likely stratigraphically segregated from more benthic-oriented and non-marine rhytidosteids, capitosauroids, and brachyopids. These distinct temnospondyl communities probably occupied a succession of regressive habitats subject to increasing hyposalinity. Finally, although integrating predominantly southern Gondwanan endemics, the Blina Shale temnospondyl assemblage apparently included some widely distributed marine taxa that may have used the contiguous Pangean coastal fringes to facilitate long-distance dispersal.