An international team of paleontologists from the United Kingdom and Germany has shown that blue feather melanosomes are highly distinct from melanosomes that are from feathers expressing black, reddish-brown, brown and iridescent.
A pigment called melanin gives black, reddish brown and gray colors to birds and is involved in creating bright iridescent sheens in bird feathers.
This can be observed by studying the melanin packages called melanosomes, which are shaped like little cylindrical objects less than one-thousandth of a millimeter and vary in shape from sausage shapes to little meatballs.
However, besides iridescent colors, which is structural, birds also make non-iridescent structural colors. Those are, for example, blue color tones in parrots and kingfishers.
Until now, it was not known if such colors could be discovered in fossils.
Paleontologists have shown that the feather itself, which is made of keratin, does not fossilize while the melanin does.
Therefore, if a blue feather fossilized, the dark pigment may be the only surviving feature and the feather may be interpreted as black or brown.
Now Dr. Frane Barbarovic from the University of Bristol and the University of Sheffield and colleagues have shown that blue feather melanosomes are distinct from melanosomes that are from feathers expressing black, reddish-brown, brown and iridescent, but overlap significantly with some gray feather melanosomes.
By looking at plumage colorations of modern representatives of fossil specimen and reconstructing which color was the most likely present in the fossil specimen, the researchers were able to discriminate between melanosomes significant for gray and blue color, leading to the reconstruction of an ancient bird species called Eocoracias brachyptera as a predominantly blue bird.
“We have discovered that melanosomes in blue feathers have a distinct range in size from most of color categories and we can, therefore, constrain which fossils may have been blue originally,” Dr. Barbarovic said.
“The overlap with gray color may suggest some common mechanism in how melanosomes are involved in making gray coloration and how these structural blue colors are formed.”
The research was published in the Journal of the Royal Society Interface.
Frane Babarović et al. 2019. Characterization of melanosomes involved in the production of non-iridescent structural feather colours and their detection in the fossil record. J. R. Soc. Interface 16 (155); doi: 10.1098/rsif.2018.0921