By Sid Perkins
Microscopic features found in fossils of dinosaurs and ancient birds are the remains of structures that contained pigment, new work reveals. The structures provide new clues about what these creatures looked like, including the possibility of patches or stripes with a sporty yellow or russet color scheme.
The fossils, some of them described for the first time, were found in northeastern China and contain well-preserved, sub-micrometer-sized structures called melanosomes, says Michael Benton, a paleontologist at the University of Bristol in England. In modern-day creatures, these pigment-bearing structures come in two forms: the cigar-shaped eumelanosomes that hold black melanin, and the egg-shaped or near-spherical phaeomelanosomes that contain pigments ranging from reddish brown through yellow. The new analyses by Benton and his colleagues, appearing online January 27 and in an upcoming Nature, are the first to report structures that appear to be phaeomelanosomes in the fossil record.
Several lines of evidence indicate that the tiny structures are melanosomes, rather than the fossilized remains of bacteria, which are about the same size and shape, says Benton. For one thing, in these fossils the structures appear within the remains of what are believed to be fossilized feathers and featherlike filaments, not on outer surfaces, where bacteria would be expected. Also, the structures are densely packed in some parts of a feather or filament but absent in similarly preserved portions nearby, whereas bacteria would be expected to indiscriminately colonize a feather on a carcass, the researchers note. Finally, the layered arrangement of the melanosomes in some of the fossils matches that seen in the feathers of some modern birds but doesn’t resemble any arrangement that bacteria might produce, says Benton.