Fossil pigments shed new light on vertebrate evolution

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.

UCC palaeontologists have discovered new evidence that the fate of vertebrate mals over the last 400 million years has been shaped by microscopic meln pigments.

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

Meln 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 mals store meln in the body, however, show that different vertebrate groups concentrate meln in different organs, revealing shifts in how mals have used meln over the last 400 million years.

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

"Most studies of fossil meln have focussed on meln in fossil feathers and skin, and what colours ancient mals had," said study leader Prof. McNamara.

"By comparing meln in different mals - how much meln they have, where in the body it occurs, what meln type and composition is present - and by studying fossils, we discovered new evidence for changes in the functions of meln through deep time," added Prof. McNamara.

The research shows that amphibians and reptiles concentrate meln in internal organs, where it supports the immune system and stores metals. In birds and mammals, however, almost all meln 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 meln in the body. Meln is hugely beneficial, but it also generates free radicals, which are harmful. This creates a major problem for mals," said team member Dr Rossi.

During the evolution of hair and feathers, mammals and birds evolved more sophisticated immune systems than in amphibians and reptiles.

This meant that large amounts of meln were no longer necessary in internal organs. Meln storage then shifted to hair and feathers, which are dead tissues, thereby removing harmful metals and free radicals from living body parts.

"Meln 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 meln 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 Prof. McNamara.

The study also shows that key genes can be mapped onto colour patterns in fossils, tracking the genetic evolution of meln through time, and that mals preferentially use less toxic forms of meln.

"There's still a lot about meln genetics and physiology that we don't understand," said Dr Ducrest of Lausanne University. What's clear, however, is that the fossil record is a valuable source of information that we can use going forwards.

( With inputs from ANI )