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.

New 'oldest bird' found in China.

For a hundred and fifty years Archaeopteryx lithographica has been the earliest known bird. The first specimen (actually a single feather) was found in 1861, in the Solnhofen limestone quarry in Bavaria, a fossil Lagerstatten (remarkable fossil bed) noted for exceptionally well preserved specimens; a number of other specimens followed. Archaeopteryx dates from the Late Jurassic, 150 million years ago. It shows clear dinosaurian affinities, but also has many birdlike features, most notably well developed flight feathers. It has been noted that had feathers not been found on Archaeopteryx, then it would probably been classified as a small dinosaur rather than a bird.

Archaeopteryx lithographica.

In the 27 July 2011 edition of the journal Nature a team lead by Xing Xu of the College of Life Science, Linyi Normal University announced the discovery of an earlier bird fossil. Xiaotingia zhengi, discovered in the Tiaojishan Formation in Liaoning, China is 155 million years old, or for convenience 'Early Late Jurassic'; fully five million years older than Archaeopteryx. Like Archaeopteryx, Xiaotingia shows both dinosaurian and avian features, though this is less remarkable than it was 150 years ago; many 'bird' features, such as feathers and wish-bones, are now known from a variety of dinosaurs. Nevertheless palaeobiological analysis of the fossil suggests that Xiaotingia is more closely related to modern birds than Archaeopteryx, and therefore can confidently be described as a bird.

Xiaotingia zhengi.

This is where things get a bit complicated. According to Xu et al. then if Xiaotingia is more closely related to modern birds than Archaeopteryx, than possibly Archaeopteryx should not be described as a bird. This is to do with the way birds are defined. If we define birds as modern birds plus all modern birds, plus their most recent common ancestor, then Archaopteryx is clearly not a bird as nobody thinks it is a direct ancestor of modern birds. Unfortunately all modern birds may well have had a quite recent common ancestor, which would mean that some Cretaceous fossils which are clearly very avian, such as Hesperornis might not be birds either.

So palaeontologists use a compromise definition, anything more closely related to modern birds than it is to Deinonychus (a dinosaur thought to be closely related to birds, but definitely not a bird) is a bird. This was fine up until now, as Archaopteryx seemed to be more like a modern bird than it seemed like Deinonychus. However Xiaotingia has more bird-like features than Archaeopteryx; producing a cladogram (family tree) for birds and bird-like dinosaurs including Xiaotingia moves Archaeopteryx closer to Deinonychus, and therefore away from the birds.

Deinonychus antirrhopus. Not a bird.

Ultimately though, this is about how we define birds as a group. Archaeopteryx clearly cannot be described as the earliest bird any more, but it should not be excluded from the group because of an artificial classification which was basically set up to rule it in and feathered maniraptiforms out. Only if good biological evidence that it is not sensible to describe Archaeopteryx as a bird comes to light should it be excluded. Sometimes technical definitions need to be tweaked to fit popular conceptions; if they did not then the definition of birds as we have it would not exist, so there is no reason to try to alter popular conceptions to fit the definition if it becomes obsolete.

See also The Ashdown Maniraptoran, An Australian Spinosaurid and Dinosaurs on Sciency Thoughts YouTube.