Wednesday 25 January 2012

Was Archaeopteryx black?

Archaeopteryx lithographica was an early bird living in Northern Europe in the Late Jurassic, about 150 million years ago. In the mid-to-late-nineteenth century several complete and partial specimens were discovered in the Solnhofen Limestone in Bavaria, when it was hailed as both the first bird and the missing link between birds and dinosaurs. Modern scientists now regard all birds to be dinosaurs, and rivals have emerged for the title of earliest bird (though Archaeopteryx is still in the running), but Archaeopteryx still remains one of the most iconic fossils of all time, as well as shedding light on a particularly interesting area in the evolution of modern life, and as such, is still studied intently.

On 24 January 2012 a paper appeared in the journal Nature Communications detailing a new study on pigmentation in Archaeopteryx, by a team lead by Ryan Carney of the Department of Ecology and Evolutionary Biology at Brown University. Carney et al. were able to isolate melanosomes (pigment cells) from a single feather discovered in Solnhofen in 1861, the first ever fossil feather found, and the first specimen to be named Archaeopteryx. They went on to compare this to four modern melanosome types from living birds; black, grey, brown and penguin (penguin melanosomes are different from those of other birds), and came to the conclusion that they were 95% certain the feather was black.

Fit for Flight. Ryan Carney discusses the pigmentation of Archaeopteryx, by The Office of Public Affairs and University Relations at Brown University.

This has lead to widespread assertions in the press and on the internet that Archaeopteryx was black, something that Carney et al. have not actually said. The study only identifies a single feather as being (probably) black, a feather that was not actually found associated with a skeletal fossil. Since this was the original fossil assigned to the species Archaeopteryx lithographica, it could be argued on the strength of this that Archaeopteryx was black, but only by excluding all other Archaeopteryx fossils from the group. In fact there have been arguments about the classification of Archaeopteryx over the years, with some scientists having assigned all the specimens to different genera (though this was overruled by the International Commission on Zoological Nomenclature) and many scientists still assigning the different specimens to different species, so in a sense the single feather is the entire species, but this is not what is being implied.

As Carney et al. have been keen to point out, melanosomes have a structural as well as a colouring role in birds, so black feathers ten to be stronger than lighter coloured feathers. Thus flight feathers (such as the one studied) are often black on birds that are not black all over, whereas down feathers, which form an insulating layer beneath the bird's outer feathers, are usually white or light in colour.

Exactly how strong a flier Archaeopteryx was is still in dispute, but even a feather evolved for a different purpose that happened to be black would hold a slight advantage over one of another colour when getting airborne, so it is interesting, but not that surprising, to discover that the flight feathers of Archaeopteryx were black (OK finding out the colour of the feather was an amazing piece of work, but finding out that colour was black is less astounding).

Comparison with modern birds suggests the colour of the flight feathers is often independent of the colour of the rest of the bird, so even if we assume that the feather does come from the animal we think of as Archaeopteryx, we cannot assume from that that the bird was in fact black.

See also A new fossil bird from the Palaeocene of Brazil, How did raptors use their claws? (and did it help them learn to fly?), Dinosaur feathers preserved in amber, Giant bird from the Cretaceous of Kazakhstan, New 'oldest bird' found in China and Birds on Sciency Thoughts YouTube.