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With regard to the art of eggs, the modern bird market is cornered. Turtles, lizards and alligators wrap their white plovers bridges, while the bird eggs appear in bright blues and chestnuts and flecks in profusion. For a long time, scientists thought that this colorful feature was entirely unique to modern birds. But our winged friends may have inherited this artistic ability directly from the dinosaurs.
Colorful eggs have only been observed once in the dinosaurs, who then transmitted the trait to their modern descendants, according to an article published this week in Nature. Scientists have discovered that egg color appeared when dinosaurs began to nest above ground, much like many modern bird species.
"This is really an important contribution to the literature, illustrating the fact that eggshell pigments have evolved much earlier than expected," says Daniel Hanley, Behavior Ecologist at the University of Long Island Post, who did not participate in the new study.
Until recently, most scientists thought that dinosaur eggs looked like old claws of reptiles. The birds were the only creatures in the history of evolution able to paint their offspring. In 2015, Jasmina Wiemann, one of the authors of the new study and molecular paleo-biologist at Yale University, published a study that revealed traces of blue-green in the eggs of the very elegant oviraptors.
Wiemann then wanted to know "Can the color of eggs have only one evolutionary origin? [the trait] to evolve twice or more independently? "
To answer this question, Wiemann and his colleagues at the American Museum of Natural History collected 20 fragments of dinosaur egg shells from around the world, as well as alligators and birds, including chickens and emus. The scientists only used dinosaur eggs where they could be sure which species they came from and which greatly restricted their sample, says Mark Norell, president of the division of paleontology of the AMNH and co-author of the new research.
In birds, all the colors and patterns of egg break down into two pigments: biliverdin, which produces blue-green, and protoporphyrin IX, which gives reddish brown. Wiemann and Norell used a technique called Raman microspectroscopy to find and measure the concentration of small amounts of these pigments in dinosaur eggs to reconstruct their colors and patterns. This technique is extremely sensitive and does not destroy the valuable eggshell samples during their analysis, says Norell.
Next, scientists mapped each colored egg on a tree of the dinosaur family (also called phylogenetic). They discovered that colored eggs appeared early in the dinosaur ancestry to Therapods, the family from which modern birds came down, when the dinosaurs stopped burying or covering their eggs, explains Norell. The timing suggests that the ability to make a pigmented egg has evolved only once, "and has not evolved near the ancestor of birds, and that it has evolved much deeper into the family tree of dinosaurs, "says Norell.
Today's reptiles bury or cover their eggs unadorned, while scientists believe that colored shells have probably evolved to protect eggs in exposed nests. Pigmented eggshells could camouflage broods laid in open nests, help birds identify their own pups to counter parasitism, filter out sunlight, keep eggs at the right temperature, and block invading bacteria when Ultraviolet light excites the brown pigment, says Hanley.
"Once you build an open nest, the egg is exposed to the environment, to potential predators, to nesting parasites, to parents," says Wiemann.[there’s a] selective pressure that promotes the evolution of the color of the egg. "
The resemblance of the egg shell could mean that we can turn to modern bird life to "predict the ecology of dinosaurs" in the past, Hanley said. "That would be super cool."
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