Extinct marine reptiles known as ichthyosaurs were warm-blooded

An international team of researchers analyzed the remains of an ichthyosaur from the Early Jurassic and found evidence that the extinct marine reptiles were most likely warm-blooded. The specimen was so extraordinarily well-preserved that the scientists were able to access samples of the creature’s original scaleless skin containing distinct epidermal and dermal layers.

Underneath the skin, the experts discovered insulating blubber that would have been useful for buoyancy and streamlining. Blubber also indicates that ichthyosaurs were homeothermic, which means they had the ability to maintain a stable internal temperature regardless of the external conditions.

“Ichthyosaurs are extinct marine reptiles that display a notable external similarity to modern toothed whales,” wrote the study authors. “Here we show that this resemblance is more than skin deep.”

According to New Scientist, study co-author Johan Lindgren of Lund University explained that all modern sea animals with blubber either maintain a constant body temperature like seals and whales, or keep their body well above the water temperature like leatherback turtles.

Scientists have also theorized that ichthyosaurs had dark backs with lighter undersides, just like many modern marine creatures. This protective coloration is known as countershading, where body parts that will be exposed to the light are dark and vice versa.

Under the microscope, the skin from the 180-million-year-old fossil appeared to have the remnants of individual pigment cells that were basically identical to those of modern reptiles, including a distinctive branched structure. This indicates that ichthyosaurs did, in fact, have countershading.

Lindgren told New Scientist: “There is more to the fossil record than we could ever imagine.”

The study is published in the journal Nature.

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By Chrissy Sexton, Earth.com Staff Writer