A field guide to mesozoic birds and other winged dinosaurs

note a correlation between porphyrin in eggshells and nesting behavior.
Pure white eggs are only found in birds which nest in shelter, such as under
dense foliage, and which constantly attend to their eggs. Species which
leave their eggs partly exposed to the elements have colorful porphyrincontaining
shells, partially for reasons of camouflage, but also possibly due
to the supposed temperature-regulating effect of porphyrins.
Theoretically, it may be possible to detect porphyrin via chemical
analysis of fossil birds. However, when restoring birds with no preserved
feathers, there should not be much for artists to consider that is not already
covered by a working knowledge of melanin coloration. Porphyrins
in feathers produce mainly only brown and dull red, colors that could also
be produced with melanin alone. If anything, porphyrins give artists license
to add extra reddish splashes to purely carnivorous species, especially those
that may have been active at night or in cold climates.
There are a variety of minor and less common pigments that can
color a bird’s feathers. Pterins are responsible for the yellow, red, white,
and orange colors of some bird eyes (in humans, eye color is controlled by
melanin; low melanin results in blue eyes, and some babies’ eyes darken as
their melanin levels increase). Flavin pigments cause many egg yolks to be
yellow. Psittacofulvins are found only in some parrots, and create yellows,
oranges, and reds in place of carotenoids, which parrots have evolved to sequester,
possibly for nutritional reasons. There are (currently undescribed)
pigments known only in penguins that add fluorescence to their yellow display
feathers.
In conclusion, Mesozoic birds would have taken their coloration
predominantly from melanin and iridescent structural coloration. This
would have resulted in a bird fauna possibly more drab overall than the
one we see around us today, due to the comparative lack of neoavians and
their ability to color their feathers with carotenoids. However, like modern
ducks, these birds would still have been able to create intricate and dazzling
displays of color and pattern using combinations of earth-toned melanins
(muted yellow, rusty red, dark grey and off-white) as well as layering of
iridescence to create striking, jewel-like feathers in blue, green, purple, and
glossy black and white. While they wouldn’t have the pinks of flamingos or
bright greens and yellows of birds-of-paradise, Mesozoic birds may have
been just as beautiful.
Opposite: Illustration of Jeholornis prima.
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