Data from: Evolutionary shifts in the melanin-based color system of birds

Melanin pigments contained in organelles (melanosomes) impart earthy
colors to feathers. Such melanin-based colors are distributed across birds
and thought to be the ancestral color-producing mechanism in birds.
However, we have had limited data on melanin-based color and melanosome
diversity in Palaeognathae, which includes the flighted tinamous and
large-bodied, flightless ratites and is the sister taxon to all other
extant birds. Here, we use scanning electron microscopy and
spectrophotometry to assess melanosome morphology and quantify reflected
color for 19 species within this clade. We find that brown colors in
ratites are uniquely associated with elongated melanosomes nearly
identical in shape to those associated with black colors. Melanosome and
color diversity in large-bodied ratites is limited relative to other birds
(including flightless penguins) and smaller-bodied basal maniraptoran
dinosaur outgroups of Aves, whereas tinamous show a wider range of
melanosome forms similar to neognaths. The repeated occurrence of novel
melanosome forms in the non-monophyletic ratites suggests that
melanin-based color tracks changes in body size, physiology or other life
history traits associated with flight loss, but not feather morphology. We
further anticipate these findings will be useful for future color
reconstructions in extinct species, as variation in melanosome shape may
potentially be linked to a more nuanced palette of melanin-based colors.