Just a few million years after the end-Permian mass extinction event (EPME), aquatic reptiles and other vertebrates had recovered to form thriving and diverse oceanic ecosystems, according to a study of an Early Triassic-age fossil site in the Arctic. The findings challenge previous assumptions of a slow and gradual establishment of mid-Triassic marine communities and suggest that vertebrate evolution paralleled the rapid resurgence of invertebrate life in the Early Triassic. The EPME, which occurred roughly 251.9 million years ago (Ma), wiped out upwards of 90% of all marine species on Earth. It has long been thought that recovery of ocean ecosystems following this event was slow, taking over eight million years. However, recent evidence indicates that, for some communities, such as invertebrates and bony fish, populations rebounded much more quickly than previously believed. The establishment and diversification of marine tetrapod communities – which first emerged in post-EPME oceans – is far less understood and is still considered to have been a long, gradual process with staged ecological complexification.

Here, Aubrey Roberts and colleagues describe new findings from the Grippia Bonebed (GBB), a mid-Early Triassic (~249 Ma) fossil site on the Arctic island of Spitsbergen in Svalbard, Norway. According to Roberts et al., the GBB fossil assemblage is notably rich, containing tens of thousands of fossils from an array of oceanic vertebrate species, and represents the earliest known marine tetrapod community from a stratigraphically constrained deposit. Using large-scale taxonomic comparisons and diversity analyses of the GBB fauna, the authors identified a highly diverse and complex marine community, composed of aquatic reptiles and amphibians, including apex-predator ichthyosaurs, smaller ichthyopterygians, durophagous ichthyosauriforms, semi-aquatic archosauromorphs, euryhaline temnospondyls, as well as a variety of fish species, all occupying multiple trophic levels. The findings suggest that many marine tetrapod lineages had already diversified and adapted to oceanic life soon after – or even before – the EPME.