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Melanosomes and the colour of ancient organisms

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The impossible seems to be true: palaeontologists can now tell the colours of fossil feathers - in ancient birds and in dinosaurs! A series of studies by different research groups, including a team from the University of Bristol and the Institute for Vertebrate Paleontology and Paleoanthropology in Beijing, have shown that fossil feathers reveal unexpected details known before only in modern feathers.

Melanin is a key colouring agent in the skin and hair of modern mammals and the feathers of modern birds. In a series of astonishing recent discoveries, the characteristic melanin-bearing organelles called melanosomes have been reported in the feathers of fossil birds and dinosaurs.

It might seem amazing that the melanosomes, and even perhaps some traces of the melanin, of ancient organisms can survive for millions of years undamaged. But melanin and melanosomes are extremely tough and are not damaged by physical or chemical agents. There is a great deal of evidence for their toughness. Nonetheless, methods of collection and study require care and ingenuity.

Melanosomes are now known in the feathers of some of the earliest birds, as well as a broad range of flesh-eating dinosaurs, from the famous Jehol deposits of China, dated at some 125 million years old, well known for their exceptional fossil preservation. These structures have also been reported from other deposits, including the Cretaceous of Brazil and the Eocene (c. 50 million years ago) of Germany.

Because feathers are such a key feature of birds, these discoveries allow scientists to understand more about the origin of birds and the behaviour of dinosaurs and early birds.

Feathers, flight, and the success of birds

Birds are hugely successful today, represented by some 10,000 species, and many biologists would explain their success by their special adaptations to flight. Birds have lightweight skeletons, to save weight, they have powerful wings and wing muscles for flight, and they have a high metabolic rate, fueled by efficient use of oxygen and excellent insulation provided by feathers. But did feathers originate for flight, insulation, or something else? Read more here

Because colour determines many aspects of behaviour, these discoveries also allow some statements about camouflage, possible warning colours, and display behaviours in dinosaurs and early birds. Further, these discoveries also open up the possibility of detailed reconstruction of the origin of feathers and hairs at a level of ultrastructural detail not yet dreamt of.

What next?

We can expect reports soon of melanosomes in the hair of fossil mammals, and perhaps in the 'hair' of pterosaurs, flying reptiles related to dinosaurs. Further, palaeontologists will probably soon locate melanosomes in other tissues, such as the black eyespots of many fossils, even as old as the Cambrian, over 500 million years ago. Richard Owen famously wrote a paper about the ink of Jurassic belemnites, using their ink, preserved black for nearly 200 million years ago. Like modern squid ink, that ancient ink probably contains melanosomes!

The discovery of colour in dinosaur feathers was announced in January 2010: the press release is here, and the paper is here. You can also see a short movie in which Mike Benton talks about the discovery. This discovery was identified as number 64 out of 100 top science stories in 2010 by Discover Magazine.


Dicynodon Illustration courtesy of John Sibbick.
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