A field guide to mesozoic birds and other winged dinosaurs

Above: Hypothetical restoration of a climbing
subadult ornithodesmid Deinonychus
antirrhopus. Non-neoavian bird coloration
was probably limited to earth tones and irridescence
due to the inability to sequester
carotenoids in the plumage.
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in most animals (some can do this, but there need to be other types of carotenoids
present to convert). Carotenoids come almost exclusively from
a diet of plants or, secondarily, of things that sequester a lot of carotenoids
in their body tissues (like plant-eating invertebrates and some fish). Gulls
living near salmon farms have shown hints of pink in their feathers: this is
because farm-raised salmon are fed artificial carotenoid sources to make
their flesh pink, and these are transferred to the birds. The most unusual
source of carotenoids, this time among a carnivorous species, is the Egyptian
Vulture, which gets its bright yellow facial skin by eating the dung of
ungulates, which yield no significant nutritional value and appears to be
consumed by the vultures only for its carotenoid content (McGraw 2006).
Indeed, while carnivores aren’t usually brightly colored, there may be selective
pressures in some species to add
unusual supplements to the diet in
order to become more colorful (Mc-
Graw 2006).
Carotenoids are often used by modern
birds as a sign of fitness when
choosing a mate. Because carotenoids
have to be eaten, a bird with a poor
diet will be drabber than a bird that is
very successful at finding food. A flamingo
kept in a zoo will turn white if
its diet isn’t artificially supplemented
with red carotenoids. Carotenoids
can also impact the eye color of a bird,
as well as beak color and the color of
the scales on its feet: even the yellow
yolk of a chicken egg (Zongker 2007)
is due to carotenoids (some birds use
Flavin for yolk color, which will be
discussed later in this chapter).
Note that even modern birds do
not have fine control of carotenoid
pigmentation in their feathers. Carotenoids
are almost always found
coloring large swaths of feathers, not
as small spots or intricate detailing
within individual feathers (Hill 2010).
Carotenoids have so far not been reported
in fossils, primarily because