Ichthyosaurs and dolphins are the archetypal examples of convergent evolution in action, in which two completely unrelated species acquire near identical characteristics.

A remarkable 180-million-year-old fossil found in the Posidonia Shale Formation of southwestern Germany, of the species Stenopterygius ichthyosaur, is providing the best evidence yet that ichthyosaurs—ancient, dolphin-like marine reptiles—were warm-blooded creatures.

What’s more, he and his colleagues were able to detect internal organs and, at the molecular scale, traces of cellular layers within the fossilised skin.

It’s now the first example of fossilised ichthyosaur blubber in the scientific literature, pointing to ichthyosaurs as warm-blooded, or endothermic, organisms.

Scientists suspected ichthyosaurs might be warm-blooded, based on estimates of their swimming speed, but this new discovery, the details of which were published yesterday in Nature, is the first to provide evidence in the form of fossilised subdermal soft-tissue.

In modern aquatic mammals, blubber, in addition to acting as an insulating layer against the cold, aids in buoyancy and serves as a fat store.

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