Color-changing, warm-blooded ichthyosaurs.

Earth Archives talks about a recent fossil discovery that changes the way we picture marine life in the age of dinosaurs:

An incredible new specimen of the Early Jurassic genus Stenopterygius found in Germany was studied by Johan Lindgren [of Lund University, Sweden] and colleagues.

The skin patch on an amazing new specimen of Stenopterygius is so exquisitely fossilized that skin cells can be seen. It shows that ichthyosaur skin was made up of distinct epidermal and dermal layers, together known as the cutus. There are no signs of scales, instead its skin appears to have been tough and rubbery like dolphins.

The epidermis also contains pigments and branching pigment cells. They show that Stenopterygius had a dark upper surface and light belly. This coloration is an example of countershading, and is common in many marine animals. Countershading helps camouflage animals, allowing them to blend in with deep water when seen from above and blend in with the sky when seen from below.

Incredibly, the branching structure of the pigment cells hints that ichthyosaurs may have been able to adjust their skin tone to lighter or darker shades.

Below the cutus is a thick layer of massive and fibrous tissue that Lindgren and colleagues interpreted as blubber. The researchers conducted experiments on porpoise skin to simulate the fossilization process, and found that the porpoise’s blubber looked almost identical to what they saw in Stenopterygius.

In living animals, blubber is only found in whales, dolphins, seals, manatees, dugongs, and leatherback turtles. Blubber helps streamline the body and provides buoyancy, but it’s only found in warm-blooded animals as its primary purpose is heat retention in frigid waters.

The presence of blubber in Stenopterygius adds to a growing list of evidence showing that ichthyosaurs, like dolphins, were also warm-blooded. This list also includes fast-growing vascularized bones, and oxygen isotope ratios in bones and teeth showing that the extremities were not significantly colder than the body’s core.

Original research here, in Nature.