Ancient sea turtle reveals pigment-based survival trait at least 54 million years old

Ancient turtles benefited from a pigmentation-based survival trait -- or dark shells -- just like their modern relatives.
By Brooks Hays  |  Oct. 17, 2017 at 9:46 AM
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Oct. 17 (UPI) -- Scientists have recovered beta-keratin and muscle proteins from the remains of an ancient sea turtle hatchling, proving modern sea turtles' pigment-based survival trait emerged at least 54 million years ago.

The turtle specimen was originally recovered from Jutland, Denmark, in 2008, and is representative of the Tasbacka danica species, which lived during the Eocene period, between 56 and 34 million years ago.

Recently, scientists were able to recover preserved tissue from the turtle remains. Biomolecular analysis revealed the presence of beta-keratin and muscle proteins, suggesting sea turtles have had dark-colored shells since at least the beginning of the Eocene.

Pigmentation of all modern sea turtle hatchlings turns their shells a dark color, helping to disguise their presence from would-be avian predators when they surface for air. Dark shells also better absorb heat, helping the cold-blooded reptiles better regulate their body temperature. Higher internal temperatures also allow the newborn and juvenile sea turtles to grow at an accelerated rate.

Early analysis of the fossils revealed the possible presence of organelles called melanosomes, which supply the skin with pigment. High-resolution imaging technologies revealed the presence of heme, eumelanin and proteinaceous molecules in the turtle's shell -- the ingredients for blood, pigment and protein -- suggesting the hatchling line indeed boasted a dark-colored shell.

The findings, combined with the biochemical analysis of the turtle's tissue, suggest ancient turtles benefited from a pigmentation-based survival trait -- just like their modern relatives.

"The presence of eukaryotic melanin within a melanosome embedded in a keratin matrix rules out contamination by microbes, because microbes cannot make eukaryotic melanin or keratin," Mary Schweitzer, a professor of biological sciences at North Carolina State University, said in a news release. "So we know that these hatchlings had the dark coloration common to modern sea turtles."

Schweitzer and her colleagues at N.C. State, as well as Lund University in Sweden and the University of Hyogo in Japan, detailed their discovery in a new paper published this week in the journal Scientific Reports.

"The data not only support the preservation of multiple proteins, but also suggest that coloration was used for physiology as far back as the Eocene, in the same manner as it is today," Schweitzer concluded.

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