A collection of tens of thousands of fossils unearthed on the island of Spitsbergen in the Svalbard archipelago (Norway), about a thousand kilometers from the Arctic, has revealed a surprising diversity of marine vertebrates, including several types of fish, amphibians and aquatic reptiles, in a period of recovery of marine life shortly after the end-Permian mass extinction (252 million years ago).
The fossil pile – called the Grippia Fossil Bed – made up of more than 30,000 pieces contained fragments of scales, bones, teeth, vertebrae, coprolites (fossilized poop) and other remains which were studied for ten years by a team of scientists from the University of Oslo Natural History Museum (Norway) and the Swedish Museum of Natural History in Stockholm (Sweden). The results were published last month in the journal Science.
Paleontologist Aubrey Roberts, a postdoctoral researcher at the University of Oslo and first author of the study, explains that the largest excavation campaign for the bones took place in August 2016 with a team made up of researchers, postgraduate students and volunteers. “Nearly a decade later, in 2024, we believe we have a good overview of the ecosystem found there after years of sorting and analyzing the material.”
A fossil bed can be defined as a “pile of bones in a rock layer” where bones from different groups of animals may be mixed together. “There is still a lot of work to do, because we have barely touched the microfossils present in the deposit, and there is still a lot of material that we have not been able to identify with certainty,” explains the scientist.
The main discovery, however, was the rich ocean fauna of what is now the Arctic (at the time it was a single global ocean called Panthalassa), including species of predatory vertebrates, such as aquatic reptiles, sharks and other marine animals.
Among the specimens found, we distinguish cartilaginous fish (sharks), lungfish (dipnoecious), bony fish (actinopterygian, similar to today’s whiting), lobe-finned fish (sarcopterygian), coelacanths, primitive amphibians (temnospondyls), archosauromorphs (ancestors of crocodiles) and ichthyosaurs and ichthyopterygian reptiles. (aquatic reptiles whose body resembles that of current dolphins).
During the Paleozoic Era, which began with the Cambrian period (550 million years ago), there was an explosion of marine life on Earth, with invertebrates and fish dominating this ecosystem until the end of the Permian, when a mass extinction event wiped out more than 90% of all known life forms. Shortly after the Permian, at the beginning of the Mesozoic era, began the so-called Age of Dinosaurs or Age of Reptiles (divided into the periods of the Triassic, 252 to 201 million years ago, the Jurassic, 201 to 145 million years ago, and the Cretaceous, 145 to 66 million years ago).
But besides dinosaurs, many other lineages of reptiles emerged and diversified beginning in the Triassic, including aquatic forms such as plesiosaurs, mesosaurs, thalatosaurs, and ichthyosaurs, which originated in the early Triassic and became extinct about 90 million years ago.
According to the authors, the big surprise was to find a variety of already derived forms (with characteristics close to the lineages whose diversification occurred a few million years later) of ichthyosaurs, since the common idea until then was that these more complex forms took at least eight million years after the end-Permian extinction to diversify. The Grippia site is estimated to be 249 million years old, only 3 million years after the end of the Permian.
“We did not expect to find such a rich diversity of ichthyosaurs, ichthyopterygians and other closely related reptiles. Ichthyosaurs were present in the seas for around 150 million years, while dinosaurs roamed the land, and were thought to have evolved and diversified after the end-Permian extinction. Our research calls this into question, with the presence of derived clades as early as the beginning of the Triassic,” says Roberts.
The new study “lowers” the approximate age of evolution of these forms. “For a single group of marine reptiles, we have evidence of at least five different species, some of them well derived, demonstrating evolution just before or just after the mass extinction,” he says.
Another interesting discovery of the research was the observation of the different ecological relationships between the vertebrates present there. While the sharks preyed on smaller fish, these were devoured by the ichthyosaurs which then occupied the top of the oceanic food chain.
Until now, localities with fossil beds of similar ages contained a high diversity of fish and amphibians, but not marine reptiles. The authors therefore assert that it is likely that the evolution of these lineages did not occur in the form of a “scale of complexity”, proposed by several scientists, but from “several opportunistic lineages which diversified and survived from the end of the Paleozoic to the beginning of the Mesozoic”.
The authors conclude that the fossil discovery suggests that the origin and evolution of marine tetrapods, particularly reptiles, occurred earlier than previously thought and, probably, in parallel with the recomposition of marine invertebrate fauna during the first million years immediately after the extinction at the end of the Permian.
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