Los ichthyosaurs They are an extinct group of marine reptiles whose fossils have been recovered from around the world. were between the first land animals to adapt to life in the open sea and developed a body shape similar to that of modern whales. While dinosaurs roamed the earth, ichthyosaurs were at the top of the food chain in the oceans, dominating marine habitats for more than 160 million years.
According to textbooks, the first reptiles that first ventured into the open sea did so after the Late Permic mass extinctionor, which devastated marine ecosystems and paved the way for the dawn of the Age of Dinosaurs, nearly 252 million years ago.
The abrupt end of the Age of Fishes
Land-footed reptiles are thought to have invaded shallow coastal environments following this catastrophic event. Over time, these early amphibious reptiles became more efficient at swimming and eventually changed their limbs into flippers, developed a fish-like body shape, and lost their attachment to dry land.
Now, however, a new set of fossils discovered in 2014 by scientists at Uppsala University on the Arctic island of Spitsbergen, are challenging this long-accepted theory. The researchers identified the bony fish remains and strange ‘crocodile-like’ amphibian bones alongside 11 jointed tail vertebrae from an ichthyosaur.
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What was unexpected about the discovery, however, is that these vertebrae were found in rocks supposedly too old for ichthyosaurs. Furthermore, rather than representing some of the amphibian ancestors of ichthyosaurs, these vertebrae are identical to those of larger-bodied, geologically much younger, and evolutionarily more advanced ichthyosaurs. In fact, they even retain the internal bone microstructure that shows adaptive characteristics of rapid growth, high metabolism, and a totally oceanic lifestyle.
Geochemical tests of the surrounding rock confirmed the age of the fossils: they dated to about 2 million years after the end-Permian mass extinction. Given the estimated timescale of the evolution of oceanic reptiles, this pushes back the origin and early diversification of ichthyosaurs before the start of the age of dinosaurs, revealing that ichthyosaurs likely entered and evolved in marine environments before the Permian extinction event.
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This discovery, the oldest ichthyosaur known to date, rewrites the popular belief that the age of the dinosaurs was the moment when the main lineages of reptiles appeared on Earth. According to the research, at least some groups of marine reptiles predated this historical interval. In fact, scientists hope to find even older fossils of these ichthyosaur ancestors in the rocks of Spitsbergen and other parts of the world.