Ichthyosaur extinction down to climate change and slow evolution

New study explains the mystery of why marine ‘sea dragons’ died out long before the end of the age of the dinosaurs.

8th March 2016
Ichthyosaur extinction down to climate change and evolution © Andrey Atuchin 2016

Ichthyosaurs – good at swimming, less so at evolution © Andrey Atuchin 2016

Not a day goes by that we hear new reasons why climate change is leading to the end of life as we know it, but it’s not just a modern affliction – it also caused problems in the age of dinosaurs.

The Ichthyosaur, a shark-like marine reptile that lived in the Mesozoic period, began swimming around the oceans some 250 million years ago. But unlike many other marine reptiles it died off tens of millions of years before the late-Cretaceous extinction, which brought about the end of the dinosaurs. Now, research published in Nature Communications has shed some light on what might have caused their early demise.

The mystery for paleobiologists is that without a major geological event, like a volcanic eruption or meteorite hitting the planet, many of the previous theories have been based on conjecture, such as increased competition for food. In this new study, scientists were able to reconstruct the evolution of the ichthyosaur over a 120-million-year period and use this create a new hypothesis as to their extinction.

What they discovered is that although the creatures, also known as sea dragons, were highly diverse in body characteristics and ecology, the rate of evolution had slowed considerably in the later periods of their existence. This turned out to be their undoing as the global climate changed and the seas became warmer relatively quickly.

First author Dr Valentin Fischer, of the University of Liège, Belgium, and the University of Oxford, explains: “Although the rising temperatures and sea levels evidenced in rock records throughout the world may not directly have affected ichthyosaurs, related factors such as changes in food availability, migratory routes, competitors and birthing places are all potential drivers, probably occurring in conjunction to drive ichthyosaurs to extinction.”

So the end of the Ichthyosaurs seems to have come from an inability to evolve fast enough to deal with the effects of global climate change. Oh well, at least there were plenty more fish in the sea.

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