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Fossil feather "melanosomes" may be bacteria (free pdf)

From: Ben Creisler

A new open access paper:

Alison E. Moyer, Wenxia Zheng, Elizabeth A. Johnson, Matthew C.
Lamanna, Da-qing Li, Kenneth J. Lacovara & Mary H. Schweitzer (2014)
Melanosomes or Microbes: Testing an Alternative Hypothesis for the
Origin of Microbodies in Fossil Feathers.
Scientific Reports 4: 4233

Microbodies associated with fossil feathers, originally attributed to
microbial biofilm, have been reinterpreted as melanosomes:
pigment-containing, eukaryotic organelles. This interpretation
generated hypotheses regarding coloration in non-avian and avian
dinosaurs. Because melanosomes and microbes overlap in size,
distribution and morphology, we re-evaluate both hypotheses. We
compare melanosomes within feathers of extant chickens with patterns
induced by microbial overgrowth on the same feathers, using scanning
(SEM), field emission (FESEM) and transmission (TEM) electron
microscopy. Melanosomes are always internal, embedded in a
morphologically distinct keratinous matrix. Conversely, microbes grow
across the surface of feathers in continuous layers, more consistent
with published images from fossil feathers. We compare our results to
both published literature and new data from a fossil feather ascribed
to Gansus yumenensis (ANSP 23403). 'Mouldic impressions' were observed
in association with both the feather and sediment grains, supporting a
microbial origin. We propose criteria for distinguishing between these
two microbodies.

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