McNamara, Maria E., Patrick J. Orr, Stuart L. Kearns, L. Alcalá, P. Anadón, and E. Peñalver Reconstructing Carotenoid-Based and Structural Coloration in Fossil Skin, Current Biology, doi: 10.1016/j.cub.2016.02.038.
Evidence of original coloration in fossils provides insights into the visual communication strategies used by ancient animals and the functional evolution of coloration over time [ 1–7 ]. Hitherto, all reconstructions of the colors of reptile integument and the plumage of fossil birds and feathered dinosaurs have been of melanin-based coloration [ 1–6 ]. Extant animals also use other mechanisms for producing color [ 8 ], but these have not been identified in fossils. Here we report the first examples of carotenoid-based coloration in the fossil record, and of structural coloration in fossil integument. The fossil skin, from a 10 million-year-old colubrid snake from the Late Miocene Libros Lagerstätte (Teruel, Spain) [ 9, 10 ], preserves dermal pigment cells (chromatophores)—xanthophores, iridophores, and melanophores—in calcium phosphate. Comparison with chromatophore abundance and position in extant reptiles [ 11–15 ] indicates that the fossil snake was pale-colored in ventral regions; dorsal and lateral regions were green with brown-black and yellow-green transverse blotches. Such coloration most likely functioned in substrate matching and intraspecific signaling. Skin replicated in authigenic minerals is not uncommon in exceptionally preserved fossils [ 16, 17 ], and dermal pigment cells generate coloration in numerous reptile, amphibian, and fish taxa today [ 18 ]. Our discovery thus represents a new means by which to reconstruct the original coloration of exceptionally preserved fossil vertebrates.