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Skin pigmentation provides evidence of convergent melanism in extinct marine reptiles
Lindgren, J.; Sjövall, P.; Carney, R.M.; Uvdal, P.; Gren, J.A.; Dyke, G.; Schultz, B.P.; Shawkey, M.D.; Barnes, K.R.; Polcyn, M.J. (2014). Skin pigmentation provides evidence of convergent melanism in extinct marine reptiles. Nature (Lond.) 506: 484-488. hdl.handle.net/10.1038/nature12899
In: Nature: International Weekly Journal of Science. Nature Publishing Group: London. ISSN 0028-0836, more
Peer reviewed article  

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Keyword
    Marine

Authors  Top 
  • Lindgren, J.
  • Sjövall, P.
  • Carney, R.M.
  • Uvdal, P.
  • Gren, J.A.
  • Dyke, G.
  • Schultz, B.P.
  • Shawkey, M.D.
  • Barnes, K.R.
  • Polcyn, M.J.

Abstract
    Throughout the animal kingdom, adaptive colouration serves critical functions ranging from inconspicuous camouflage to ostentatious sexual display, and can provide important information about the environment and biology of a particular organism. The most ubiquitous and abundant pigment, melanin, also has a diverse range of non-visual roles, including thermoregulation in ectotherms. However, little is known about the functional evolution of this important biochrome through deep time, owing to our limited ability to unambiguously identify traces of it in the fossil record2. Here we present direct chemical evidence of pigmentation in fossilized skin, from three distantly related marine reptiles: a leatherback turtle5, a mosasaur and an ichthyosaur. We demonstrate that dark traces of soft tissue in these fossils are dominated by molecularly preserved eumelanin, in intimate association with fossilized melanosomes. In addition, we suggest that contrary to the countershading of many pelagic animals, at least some ichthyosaurs were uniformly dark-coloured in life. Our analyses expand current knowledge of pigmentation in fossil integument beyond that of feathers, allowing for the reconstruction of colour over much greater ranges of extinct taxa and anatomy. In turn, our results provide evidence of convergent melanism in three disparate lineages of secondarily aquatic tetrapods. Based on extant marine analogues, we propose that the benefits of thermoregulation and/or crypsis are likely to have contributed to this melanisation, with the former having implications for the ability of each group to exploit cold environments.

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