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Fossil feather colors questioned
From: Ben Creisler
A couple of new papers and a news item on the topic of what color
feathers really were in fossil animals:
Maria E. McNamara, Derek E. G. Briggs, Patrick J. Orr, Daniel J. Field
and Zhengrong Wang (2013)
Experimental maturation of feathers: implications for reconstructions
of fossil feather colour.
Biology Letters 9(3): 20130184 (advance online publication)
pdf is free!
Fossil feathers often preserve evidence of
melanosomes—micrometre-scale melanin-bearing organelles that have been
used to infer original colours and patterns of the plumage of
dinosaurs. Such reconstructions acknowledge that evidence from other
colour-producing mechanisms is presently elusive and assume that
melanosome geometry is not altered during fossilization. Here, we
provide the first test of this assumption, using high pressure–high
temperature autoclave experiments on modern feathers to simulate the
effects of burial on feather colour. Our experiments show that
melanosomes are retained despite loss of visual evidence of colour and
complete degradation of other colour-producing structures (e.g.
quasi-ordered arrays in barbs and the keratin cortex in barbules).
Significantly, however, melanosome geometry and spatial distribution
are altered by the effects of pressure and temperature. These results
demonstrate that reconstructions of original plumage coloration in
fossils where preserved features of melanosomes are affected by
diagenesis should be treated with caution. Reconstructions of fossil
feather colour require assessment of the extent of preservation of
various colour-producing mechanisms, and, critically, the extent of
alteration of melanosome geometry.
Daniel J. Field, Liliana D’Alba, Jakob Vinther, Samuel M. Webb,
William Gearty & Matthew D. Shawkey (2013)
Melanin Concentration Gradients in Modern and Fossil Feathers.
PLoS ONE 8(3): e59451.
In birds and feathered non-avian dinosaurs, within-feather
pigmentation patterns range from discrete spots and stripes to more
subtle patterns, but the latter remain largely unstudied. A ~55
million year old fossil contour feather with a dark distal tip grading
into a lighter base was recovered from the Fur Formation in Denmark.
SEM and synchrotron-based trace metal mapping confirmed that this
gradient was caused by differential concentration of melanin. To
assess the potential ecological and phylogenetic prevalence of this
pattern, we evaluated 321 modern samples from 18 orders within Aves.
We observed that the pattern was found most frequently in distantly
related groups that share aquatic ecologies (e.g. waterfowl
Anseriformes, penguins Sphenisciformes), suggesting a potential
adaptive function with ancient origins.
Also see this news item in Nature: