Melanins in Fossil Animals: Is It Possible to Infer Life History Traits from the Coloration of Extinct Species?

Juan Negro,Ismael Galván,Clive Finlayson

doi:10.3390/ijms19020230

Abstract

Paleo-colour scientists have recently made the transition from describing melanin-based colouration in fossil specimens to inferring life-history traits of the species involved. Two such cases correspond to counter-shaded dinosaurs: dark-coloured due to melanins dorsally, and light-coloured ventrally. We believe that colour reconstruction of fossils based on the shape of preserved microstructures—the majority of paleo-colour studies involve melanin granules—is not without risks. In addition, animals with contrasting dorso-ventral colouration may be under different selection pressures beyond the need for camouflage, including, for instance, visual communication or ultraviolet (UV) protection. Melanin production is costly, and animals may invest less in areas of the integument where pigments are less needed. In addition, melanocytes exposed to UV radiation produce more melanin than unexposed melanocytes. Pigment economization may thus explain the colour pattern of some counter-shaded animals, including extinct species. Even in well-studied extant species, their diversity of hues and patterns is far from being understood; inferring colours and their functions in species only known from one or few specimens from the fossil record should be exerted with special prudence.

Highlights

Color reconstruction in fossil species is an exciting scientific topic adding a realistic and more vivid touch to our perception of life on Earth in a distant past
Brown et al [10], in turn, remarked the fact that Borealopelta was much larger than any extant species showing countershading, and that it must have been preyed upon by gigantic predatorial dinosaurs
Many authors have remarked that both types of processes may operate together: natural selection typically concealing animals in their environment, and sexual selection acting in the opposite way, making animals more conspicuous [18]

Summary

Introduction

Color reconstruction in fossil species is an exciting scientific topic adding a realistic and more vivid touch to our perception of life on Earth in a distant past. Brown et al [10], in turn, remarked the fact that Borealopelta was much larger than any extant species showing countershading, and that it must have been preyed upon by gigantic predatorial dinosaurs This would be proof that predator–prey dynamics in the Jurassic are different compared to today. Many authors have remarked that both types of processes may operate together: natural selection typically concealing animals in their environment, and sexual selection acting in the opposite way, making animals more conspicuous (at least at close range) [18] This is an oversimplification, and animal colors may have evolved by natural selection for a number of reasons, including physical protection in the environment, concealment, advertising, and deception. The mimic is generally less poisonous or less powerful than the model

Mechanistic Considerations

Functional Considerations