COLOUR PATTERNS IN A FOSSIL SNAKE

Evidence of original coloration in fossils can provide insights into the visual communication strategies used by ancient animals and into the functional evolution of coloration mechanisms over time. A recent focus of research has been the color of fossil feathers, especially those of feathered dinosaurs, but the original colors of non-feathered dinosaurs and other reptiles remains obscure. This is due, in part, to the low preservation potential of skin (and color-producing structures therein) relative to feathers. Here we report exceptional preservation of skin in a 10 Ma colubrid snake from the Late Miocene Libros Lagerstätte of NE Spain. The skin is replicated in three dimensions in calcium phosphate; preserved ultrastructural features include epidermal layering, various upper dermal pigment glands, i.e. melanophores, xanthophores and iridophores, pigment granules, dermal collagen fibres and extracellular matrix; basal membrane / fascia and subdermal musculature are also preserved. The relative abundance of the different pigment glands varies over the body surface, allowing the original colors of the snake to be inferred. Ventral body regions contain notably fewer pigment glands than more dorsal regions, indicating that the former were pale in colour and suggesting that this feature of snake coloration has been conserved for at least the last 10 Ma. Examples of skin replicated in calcium phosphate should be targeted as part of future attempts to infer original coloration of non-feathered dinosaurs.