This ancient marine reptile had more in common with whales

The Stenopterygius ichthyosaur, an ancient marine reptile that inhabited the oceans during the Jurassic Period, had many traits in common with dolphins and whales. However, given that species are not close relatives, these shared traits have puzzled scientists.

But now, a new study is helping to shed light on the biological traits of the Stenopterygius ichthyosaur.

An international team of researchers, led by Johan Lindgren from Lund University in Sweden, conducted a thorough molecular and microstructural analysis of a Stenopterygius fossil that dates back nearly 180 million years. The research was published in the journal Nature.

“Ichthyosaurs are interesting because they have many traits in common with dolphins, but are not at all closely related to those sea-dwelling mammals,” said Mary Schweitzer, a co-author of the study. “We aren’t exactly sure of their biology either. They have many features in common with living marine reptiles like sea turtles, but we know from the fossil record that they gave live birth, which is associated with warm-bloodedness. This study reveals some of those biological mysteries.”

Image Credit: Johan Lindgren

The fossil is exceptional and researchers were even able to extract soft tissue samples and study the cells of the marine reptile.

“Both the body outline and remnants of internal organs are clearly visible,” said Johan Lindgren. “Remarkably, the fossil is so well-preserved that it is possible to observe individual cellular layers within its skin.”

Researchers identified microstructures that held pigments within the reptile’s skin and even traces of the liver. The study is the first of its kind to find evidence that ichthyosaurs had insulating layers of blubber like whales.

“This is the first direct, chemical evidence for warm-bloodedness in an ichthyosaur, because blubber is a feature of warm-blooded animals,” said Schweitzer.

The results suggest that even though Stenopterygius ichthyosaur was a reptile, it had much more in common with whales and dolphins including dark coloring on top to help camouflage from predators, warm-bloodedness, and blubber.

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By Kay Vandette, Earth.com Staff Writer