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More than 30,000 teeth, bones and other fossils from a 249 million-year-old community of extinct marine reptiles, amphibians, bony fish and sharks have been discovered on the remote Arctic island of Spitsbergen. These record the earliest radiation of land-living animals into oceanic ecosystems following cataclysmic extinction and extreme global warming at the dawn of the Age of Dinosaurs.

The fossils were found in 2015, but took nearly a decade of painstaking work to excavate, prepare, sort, identify, and analyze. The long-awaited research findings have now been published by a team of Scandinavian paleontologists from the Natural History Museum at the University of Oslo, and the Swedish Museum of Natural History in Stockholm.

The paper is in the journal Science.

Spitsbergen in the Svalbard archipelago is world famous for producing marine fossils from the beginning of the Age of Dinosaurs. These are preserved in rock layers that were once mud at the bottom of a sea stretching from mid-to-high paleolatitudes and bordering the immense Panthalassa super-ocean. Most spectacular are the remains of bizarre marine reptiles and amphibians that represent the earliest adaptive specialization of land-living animals for life in offshore habitats.

The aftermath of Earth's greatest extinction

Textbooks suggest that this landmark evolutionary event took place after the most catastrophic mass extinction in Earth history, some 252 million years ago. Termed the end-Permian mass extinction, this "great dying" wiped out over 90% of all marine species, and was driven by hyper-greenhouse conditions, oceanic deoxygenation, and acidification linked to massive volcanic eruptions initiating the breakup of the ancient Pangaean supercontinent.

Timing the recovery of marine ecosystems after the end-Permian mass extinction is one of the most debated topics in paleontology today. The long-standing hypothesis is that this process was gradual, spanning some eight million years, and involved a stepwise evolutionary progression of amphibians and reptiles successively invading open marine environments. However, the discovery of the new and exceptionally rich fossil deposit on Spitsbergen has now upended this traditional view.

The Spitsbergen fossil deposit is so dense that it actually forms a conspicuous bonebed weathering out along the mountainside. This accumulated over a very short geological timeframe, and therefore provides unprecedented insights into the structure of marine communities from only a few million years after the end-Permian mass extinction. Stratigraphic dating has pinpointed the age of the Spitsbergen fossil bonebed to around 249 million years ago.

Revealing a rapid recovery and rich diversity

Careful collection of the remains from 1 m² grids covering 36 m² has also ensured that over 800 kg of fossils, including everything from tiny fish scales and shark teeth to giant marine reptile bones and even coprolites (fossilized feces) were recovered.

The Spitsbergen fossil bonebed reveals that marine ecosystems bounced back extremely rapidly, and had established complex food chains with numerous predatory marine reptiles and amphibians by as little as three million years after the end-Permian mass extinction. Most surprising is the sheer diversity of fully aquatic reptiles, which included archosauromorphs (distant relatives of modern crocodiles) and an array of ichthyosaurs ("fish-lizards") ranging in size from small squid-hunters less than one meter long to gigantic apex-predators exceeding five meters in length.

A computer-based global comparative analysis of the various animal groups further highlights the Spitsbergen fossil bonebed as one of the most species-rich marine vertebrate (backboned animal) assemblages ever discovered from the dawn of the Age of Dinosaurs. It also suggests that the origins of sea-going reptiles and amphibians are much older than previously suspected, and likely even preceded the end-Permian mass extinction.

This ecosystem reset would have opened new feeding niches, and ultimately, laid the foundations for modern marine communities as we know them today.