Dolphins and ichthyosaurs are a classic example of convergent evolution—the separate species independently evolving similarly streamlined shapes.

A recent discovery, however, suggests the Jurassic-era “fish lizard” had more in common with modern whales than we thought.

A 180-million-year-old ichthyosaur fossil, found in southwest Germany, provides the best evidence yet that Stenopterygius ichthyosaur were warm-blooded creatures.

“You can clearly see both the body outline and remains of internal organs,” lead researcher Johan Lindgren, of Lund University in Sweden, said in a statement. “We can even distinguish the different cellular layers within the skin.”

Representation of the 85-cm-long fossil (which corresponds to roughly half of the original length of the animal) (via Johan Lindgren)

Fossil preservation was so good, in fact, that Lindgren and his team were able to identify blubber underneath the skin. That thick layer of soft tissue, present in modern marine mammals, suggests that ichthyosaurs had metabolic rates higher than most reptiles living today.

Which, according to Lund University, helps explain the ancient animal’s almost-global distribution—even in cold waters—as well as their ability to dive to considerable depths and grow rapidly.

Scientists also examined remains of the so-called “sea monster”‘s liver, which included part of its original biochemistry.

“It’s truly remarkable that the biomolecules we discovered so closely match the tissues that we could identify,” Lindgren said.

On a more queasy note, researchers revealed the fossils contain tissues that “retain a certain degree of elasticity,” even 180 million years after the material was fresh.

Comparison between artificially matured modern porpoise integument (left and center) and fossil ichthyosaur blubber (right) (via Johan Lindgren & Martin Jarenmark)

Their results, published in the journal Nature, also reveal the coloring of adult ichthyosaurs: a dark upper body and light belly, which acted either as camouflage or UV protection—or both.

“Not only do the results provide insights into the biology, physiology, and ecology of derived ichthyosaurs, they also show how little we know about the fossilization process and what can actually be preserved in the fossil record,” a University press release said.

“Moreover,” it continued, “they could add to our knowledge on convergent evolution, as ichthyosaurs display an interesting mix of characteristics otherwise found in tooth whales (such as dolphins and porpoises) and the leatherback sea turtle.”

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