The recovery of life from the devastating end-Permian mass extinction, which peaked about 252.3 million years ago, was an important period of evolution. Whether biodiversity had to rebuild from near annihilation or from refugia is a matter of conjecture but recovery heralded the development of recognizably modern ecosystems. Paleontologists have now discovered an exceptionally preserved fossil assemblage in the Daye Formation near Guiyang, China. Named Guiyang Biota, the assemblage is dated to 250.83 million years ago (nearly one million years after the extinction event) and presents examples of diverse fishes, ammonoids, bivalves, protists, and malacostracan arthropods.

Field photo of the fossilized remains of a fish called Watsonulus, a member of the Guiyang Biota. Image credit: Xu Dai.

The end-Permian mass extinction, also known as the Permian-Triassic extinction event and the Great Dying, is the most severe extinction event in the past 540 million years.

This catastrophe, which peaked about 252.3 million years ago, killed off nearly 96% of all marine species and 70% of terrestrial vertebrate species on the planet over the course of thousands of years

Massive eruptions in a volcanic system called the Siberian Traps are thought to have played an important role, but the causational trigger and its feedbacks are yet to be fully understood.

The recovery of marine life following the extinction and during the Early Triassic epoch is widely considered to be a major period of evolutionary changes that laid the foundation for the ecosystems that dominate oceans today.

However, due to the relative scarcity of marine fossils dating back to this critical period, the evolution of marine biota in the wake of the mass extinction is poorly understood.

“The fossils of the Guizhou region reveal an ocean ecosystem with diverse species making up a complex food chain that includes plant life, bony fish, ray-finned fish, crabs, lobsters, shrimp, and mollusks,” said Dr. Morgann Perrot, a paleontologist at the Université du Québec à Montréal.

“We discovered 12 classes of organisms and even found fossilized feces, revealing clues about the diets of these ancient animals.”

An illustration depicting the onset of the end-Permian mass extinction. Image credit: Dawid Adam Iurino / PaleoFactory, Sapienza University of Rome / Jurikova et al, doi: 10.1038/s41561-020-00646-4.

According to the team, the Guiyang Biota represents the oldest known Mesozoic lagerstätte and provides an unprecedented snapshot of a marine ecosystem only one million years after the end-Permian mass extinction.

It represents a highly diversified and trophically complex marine ecosystem comprised of a wide array of predatory fishes, crustaceans, ammonoids, and bivalves.

Although the Guiyang Biota remains incompletely sampled, it highlights that the slow and stepwise recovery model after the end-Permian mass extinction is not applicable.

“Previously, it was thought that complex ecosystem would need 5-10 million years to evolve after an extinction,” Dr. Perrot said.

“However, we found that the specimens in the Guizhou region evolved much quicker than that by using radiometric dating to date the rocks where the fossils were discovered.”

“All of this has implications for our understanding of how quickly life can respond to extreme crises. It also necessitates a re-evaluation of early Triassic ocean conditions.”