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Researchers determine coloring of ancient marine reptiles

Pigment molecules extracted from fossils can be analyzed to reveal prehistoric skin colors

Researchers such as Ryan Carney GS can now determine the skin color of extinct reptiles — knowledge that can lead to insight about their behaviors.

Carney and his colleagues performed a detailed chemical analysis of reptilian pigment molecules, with the resulting study published in Nature Jan 8.

“Our results provide the very first evidence of pigment molecules in fossilized skin, which therefore opens the door for reconstructing the colors of many more types of extinct creatures,” Carney said in a University press release. Previously, these pigments could only be isolated from feathers, he said.

The team’s experiments used the latest technique available, which allowed them to “analyze molecules and molecular fragments,” said Johan Lindgren, co-author of the study and senior lecturer at Lund University in Sweden. This technology is called Time-of-Flight Secondary Ion Mass Spectrometry and allows the researchers to detect and analyze pigment molecules. They then compare them to a collection of known molecular fingerprints to determine what color they would have been, Carney said.

The major breakthrough that allowed for this sort of pigment study occurred in 2008 when University of Bristol Lecturer Jakob Vinther, a co-author of the study, discovered that melanin granules — a type of pigment — can be isolated from squid and insect fossils.

This prompted a “giant leap forward in the technology,” Carney said. Scientists previously could only examine the dimensions and shapes of melanosomes, which are organelles that synthesize and transport melanin. Now scientists can closely analyze the pigment molecules themselves, he said.

For their study, Carney said, the researchers chose two large, extinct marine reptiles — the ichthyosaur and the mosasaur — because their skin was well-preserved and dark, which indicated a presence of melanin.

In their study, they compared the molecules from these fossils to a modern leatherback turtle, Lindgren said. “The leatherback turtle is an interesting animal, and it’s also one of the only marine turtles that are actually left,” he added.

Carney said the spectrum from the fossils matched modern eumelanin — an indicator of black or brown coloring — from squid, feathers and other fossils.

Adult leatherback turtles are also very dark, which is believed “to allow them to absorb radiation and survive in colder environments,” Carney said. He and his team think this could be a reason fossilized animals “found in arctic, cold environments” each independently evolved this dark coloration, Carney added.

All three of the marine creatures Carney studied were “secondarily aquatic, and all three were very dark, large and able to live in colder habitats,” Carney said.

Carney said the presence of melanin in these distantly related organisms that inhabited a similar environment indicates convergent evolution, which suggests that melanin “had a role that was related or at least correlated with their marine habitat,” he added. For example, sea turtles and deep diving whales have very dark coloration, which “allows them to maintain camouflage in low-light environments,” he said.

Lindgren said the potential for future research is significant. Because researchers can now visualize some of the coloration in ancient animals, they can infer certain behaviors, he said.

Carney said one important lesson from this research is “the fact that compounds can be preserved molecularly for such a long time.” The ichthyosaur is 200 million years old, but researchers were still capable of finding sources of pigment because “melanin is robust,” he said.

The advance in technology is an “awesome technique for pinpointing molecular signatures and things we never thought could have existed in the fossil records,” he added.


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