Nothing opens up the possibility for evolutionary oddballs to emerge quite like a mass extinction. The worst such catastrophe – the Permian-Triassic mass extinction, about 252 million years ago – so dramatically cut back the world’s biodiversity that the relatively few survivors stepped into an open world where entirely novel forms of life could evolve.

Triassic reptiles, in particular, underwent an evolutionary explosion in the aftermath of the disaster, and within that proliferation multiple lineages of the scaly vertebrates started to slide into the sea. Fish-like ichthyosaurs, shell-crushing placodonts, and the quad-flippered ancestors of plesioaurs were among the most famous lineages to take the plunge, but paleontologists have recently started to turn up even