Well-preserved fossil assemblage suggests marine ecosystem recovery after the “great dying” happened rapidly

An exceptionally preserved fossil assemblage from China reveals that the rise of a modern-type marine ecosystem after the Permian-Triassic mass extinction – also known as the “great dying” – happened sooner than scientists have thought. The study’s authors say their finding “forces us to rethink interpretations of this recovery,” which some have proposed happened in a slow, stepwise way, but which this study’s findings suggest as unlikely. The ecological structure of modern-day marine ecosystems arose after the Permian-Triassic mass extinction (PTME), which occurred roughly 252 million years ago. This extinction resulted in the eradication of great swaths of Earth’s life, including more than 80% of Earth’s marine species. The recovery of marine life following the extinction and during the Early Triassic 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 PTME is poorly understood. Here, Xu Dai and colleagues report on the Guiyang Biota, a finely preserved Early Triassic marine fossil lagerstätte from the Daye Formation in South China. The assemblage of marine fossils, dated to ~250.8 million years ago, represents the oldest known Mesozoic lagerstätte and provides an unprecedented snapshot of a marine ecosystem only one million years after the PTME. According to Dai et al., the Guiyang Biota 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 PTME is not applicable,” the authors say.