Saturday, August 29, 2009

Extinct Iridescence

Photo credit: Jakob Vinther/Yale University

A study announced this week determined that some ancient birds had iridescent black feathers, much like modern grackles or starlings. The analysis is based not on some new discovery but on fossils that had been stored in a museum collection. The example shown above, one of the fossils used in the study, does not look particularly glossy or black, at least not to my eye. However, ornithologists were able to reconstruct its original appearance based on the structure of pigmentation.
"[The arrangement of melanosomes] implies that this guy had a black plumage with a very glossy metallic, coppery, greenish, or bluish sheen to it," said Prum, whose new research appears online today in the journal Biology Letters.

The exact details of the iridescent color depend on how light would have reflected off the melanosomes and the layer of keratin, or protein, just above them. The keratin layer decomposed during fossilization.

"What you see is a beautifully smooth surface made of the melanosomes packed together," Prum said.

"And that beautiful smooth surface is the kind of uniform layer that characterizes the melanin distribution within an iridescent feather. We don't see that in a crow or other plain black bird."
The linked article includes a note of caution from another ornithologist to the effect that fossils provide incomplete information about an organism's color. The loss of keratin in particular might change how a fossil appears in the lab. However, it is still and interesting finding, and I am excited at the prospect of more accurate depictions of these long-extinct animals.