Dark and dangerous
A microscopic look at the fossils showed oval bodies consistent with the look of melanosomes. To confirm that the oval bodies were melanosomes, the researchers used a technique called energy-dispersive X-ray microanalysis, which focuses X-rays on the sample. The reaction of the sample depends on its chemical makeup. This analysis showed that the tiny ovals were associated with the preserved skin film, but not with the sediment around it, suggesting they are really melanosomes and not microbial contamination.
To understand how ancient sea creatures benefited from black skin and scales, Lindgren and his colleagues turned to the only sea turtle that stays black into adulthood: the modern leatherback turtle (Dermochelys coriacea). These turtles have a broad range, all the way into the Arctic circle, and the color seems to help them trap heat from sunlight in the same way that black asphalt gets hot on a bright day, Lindgren said. Black pigments also protect the skin from damage from UV rays (also known as sunburn). Mosasaurs, ichthyosaurs and ancient may have gotten a similar advantage from their coloration.
Black skin and scales may also have helped these creatures stay stealthy in the dark seas. Living leatherback turtles are dark on top with light underbellies, so they blend in with the depths from above and with the sunlight at the surface from below. Many ocean-dwelling creatures show this coloration pattern, Lindgren said, but the fossil skin samples from the ancient turtle and mosasaur are too small to say for sure whether they shared countershading camouflage.
Ichthyosaurs are a different story. Some ichthyosaur fossils consist of skeletons surrounded completely by an "envelope" of dark material. If these envelopes prove to be entirely skin remains, Lindgren said, they would suggest that ichthyosaurs were completely black. That coloration would make them like modern sperm whales, which dive deep into murky waters — as ancient ichthyosaurs also may have done.
"Of course, that may be a coincidence, but it's an interesting similarity that they share," Lindgren said.
The techniques used in the study may also be able to resolve debate over the coloration of land animals, he said, differentiating whether suspected melanosomes come from the fossil or from microbes.
Original article on LiveScience.
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