Geoscientist Online

Palaeontologists discover pigment organelles in Cretaceous and Eocene fossil bird feathers and eyes, reports Dwain Eldred

Geoscientist Online 9 July 2008

Traces of organic material found in fossil feathers are remnants of pigments that once gave birds their colour, according to scientists at Yale University, writing in the journal Biology Letters. The discovery opens up the possibility of depicting the original coloration of fossil birds and even their ancestors the dinosaurs.

Closer study of a number of fossilised bird feathers by Yale PhD student Jakob Vinther revealed that tiny organic imprints in the fossils - previously thought to be carbon traces from bacteria - are in fact fossilised melanosomes, the subcellular organelles that contain the pigment melanin.

"Birds frequently have spectacularly coloured plumage which is often used in camouflage and courtship display" says Vinther. "Feather melanin is responsible for rusty-red to jet-black colours, and a regular ordering of melanin even produces glossy iridescence. These … fossil feathers also demonstrate that melanin can resist decay for millions of years."

Working with palaeontologist Derek Briggs and ornithologist Richard O Prum, Vinther analysed a striped feather found in Lower Cretaceous rocks from Brazil. The team used a scanning electron microscope to show that dark bands of the feather preserved the arrangement of the pigment-bearing structures as a carbon residue — organised much as the structures are in a modern feather. The light bands showed only rock surface.

Bird's eye

In another fossil, of a bird from the Danish Eocene (55 million years old) they found similar traces in feathers surrounding the skull. That fossil also preserved an organic imprint of the bird's eye and showed structures similar to melanosomes found in the eyes of modern birds.

"Many other organic remains will presumably prove to be composed of melanin" says Vinther. He expects that fur of ancient mammals and skin from dinosaurs preserved as organic imprints will likely be the remains of melanin. "Now that we have demonstrated that melanin can be preserved in fossils, scientists have a way to reliably predict, for example, the original colours of feathered dinosaurs" says Prum.