Fossilised snake shows its true colours

Fossilised snake shows its true colours - The colours of the skin of a 10 million year old Spanish snake have been discovered from its colourless fossil remains by scientists at University College Cork (UCC).

Research by Dr Maria McNamara, UCC and her team have found that some fossils can retain evidence of skin colour from multiple pigments and structural colours depending on the conditions in which they fossilized which will aid research into the evolution and function of colour in animals. This research will be published by the international journal, Cell Biology.

Ten million years ago, a green and black snake lay coiled in the Spanish undergrowth. Once, scientists would have been limited to the knowledge they could glean from its colourless fossil remains, but now they know what the snake looked like and can guess how it acted.

So far, scientists filling the ancient-Earth colouring book with pigment have been limited to browns, blacks, and muddy reds when melanin lasts as organic material. No other pigments have been shown to survive fossilisation. But this snake’s skin was fossilised in calcium phosphate, a mineral that preserves details on a subcellular level.

The fossilised snakeskin maintained the unique shapes of different types of pigment cells, which would have created yellows, greens, blacks, browns, and iridescence while the animal was alive. The pigments themselves are now decayed, but with the cell shapes—specific to each kind of pigment—mineralized, there’s enough information to reconstruct their colours.

“When you get fossil tissues preserved with this kind of detail, you’re just gobsmacked when you’re looking at it under the microscope,” says first author Maria McNamara, a palaeobiologist at the School of Biological, Earth and Environmental Sciences at UCC. “I was astounded. You almost can’t believe what you’re seeing.”

McNamara first came across the fossilised snake while conducting her PhD research on fossils from the Libros site in Spain, but she only recently analysed the specimen. Her team discovered the mineralised skin cells when viewing the fossil under a high-powered scanning electron microscope and then matched the shapes up with pigment cells in modern snakes to determine what colours they might have produced.

“For the first time, we’re seeing that mineralised tissues can preserve evidence of colour,” says McNamara. The researchers determined that the fossilised snakeskin had three types of pigment cells in various combinations: melanophores, which contain the pigment melanin; xanthophores, which contain carotenoid and pterin pigments; and iridophores, which create iridescence. All told, the snake was a mottled green and black, with a pale underside—colours that likely aided in daytime camouflage.

“Up until this discovery, the only prospect for skin colour being preserved in fossils was organic remains related to melanin,” says McNamara. “But now that we know colour can be preserved even for tissues that are mineralised, it’s very exciting.”

Calcium phosphate mainly shows up in fossil bones and shells, but records do exist of so-called phosphatised skin. This discovery opens the door for re-analysis of these fossils, occurring across a wide range of creatures and locations, for evidence of colour preservation. And knowing the colour of an animal can also clue researchers in to some aspects of its behaviour and evolution.

“It’ll mean re-evaluating a lot of specimens that might have been overlooked,” says McNamara.

The funding for the research was provided by Enterprise Ireland, the Irish Research Council and a Marie Curie International Mobility Fellowship, and a Marie Curie Career Integration Grant from the EU.

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