Fossil pigments shed new light on vertebrate evolution

The research shows that amphibians and reptiles concentrate melanin in internal organs, where it supports the immune system and stores metals.

Washington: UCC palaeontologists have discovered new evidence that the fate of vertebrate animals over the last 400 million years has been shaped by microscopic melanin pigments.

This new twist in the story of animal evolution is based on cutting-edge analyses of melanin granules – melanosomes – in many different fossil and modern vertebrates, including fish, amphibians, reptiles, birds, and mammals.

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Melanin and melanosomes have traditionally been linked to outermost body tissues such as skin, hair, and feathers, with important roles in UV protection and stiffening of tissues. Analyses of where different animals store melanin in the body, however, show that different vertebrate groups concentrate melanin in different organs, revealing shifts in how animals have used melanin over the last 400 million years.

The study, published in the journal Trends in Ecology and Evolution, was led by UCC palaeontologists Maria McNamara, Dr Chris Rogers, Dr Valentina Rossi and PhD student Tiffany Slater, with an international team of evolutionary biologists from Switzerland.

The research shows that amphibians and reptiles concentrate melanin in internal organs, where it supports the immune system and stores metals. In birds and mammals, however, almost all melanin occurs in hair and feathers. This difference has an unexpected source – evolution of the immune system and of warm-blooded lifestyles.

“There are pros and cons to having melanin in the body. Melanin is hugely beneficial, but it also generates free radicals, which are harmful. This creates a major problem for animals,” said team member Dr Rossi.

“Melanin is a two-sided coin. It’s useful, but toxic. Birds and mammals basically came up with an ingenious solution during the early Triassic – pump melanin into new, outer, dead skin tissues that were evolving at the time. This set the scene for the evolution of the incredible diversity of plumage and fur patterning which we see today,” said McNamara.