Artistic view of the diversified and complex Early Triassic marine ecosystem of southeastern Idaho as revealed by the Paris Biota. Jorge Gonzalez

The palaeontological orthodoxy that the world took millions of years to recover from the end-Permian mass extinction has been powerfully challenged by the discovery of a rich and varied ecosystem dating to just after the event.

A research team led by Arnaud Brayard at University of Burgundy – Franche-Comté in France analysed a large haul of fossils uncovered near the town of Paris in Idaho, US, and found “a phylogenetically diverse, functionally complex, and trophically multileveled marine ecosystem” – including a type of sponge thought to have gone extinct 200 million years before.

The haul – dubbed the Paris Biota – dates from about 250 million years ago – almost immediately after the end of what evolutionary historians call “the great dying”.

The end-Permian mass extinction saw the demise of 96% of all marine species and around 70% of all terrestrial vertebrates and followed a period of intense global climate change, ocean acidification and fluctuating water temperatures.

The Early Triassic, which followed the Permian, is usually considered a period of stark biological scarcity worldwide. However, the new finding suggests that on parts of the sea floor, at least, things weren’t so bleak.

“Unlike previous works that suggested a sluggish post-crisis recovery and a low diversity for the Early Triassic benthic organisms, the unexpected composition of this exceptional assemblage points toward an early and rapid post-Permian diversification for these clades,” the researchers write in Science Advances.

As well as boasting a surprising 20 distinct Metazoan orders, the fossil assemblage – preserved in limestone and shale in a shallow section of the western US basin – also contains primitive cephalopods, sponges and algae, some previously thought to have evolved 50 million years later.

The fossils include top predators, primary producers and scavengers, bearing characteristics of much later organisms. The researchers say this co-existence shows a “faunal transition” into modern marine life, the exact timing of which remains unknown.

View of a sampled slab from the Paris Biota showing fish scales and shrimp. Arnaud Brayard

“The Paris Biota highlights the key evolutionary position of Early Triassic fossil ecosystems in the transition from the Paleozoic to the Modern biosphere,” the researchers explain, adding that the finding shows “that the rise of the modern evolutionary fauna at least sometimes emerged from taxonomically, phylogenetically, and ecologically diverse communities.”

The researchers have called the find “remarkable”, touting it as “a new landmark for understanding the marine recovery dynamics” after the world’s most severe extinction.