Two, some parent birds use spot patterns to recognize their own eggs if they live in large colonies (or to prevent freeloading birds, like cuckoos, from sneaking their eggs into a brood). And last year, molecular paleobiologist Jasmina Wiemann of Yale University published the first evidence of dinosaur egg coloration, using chemical analysis to detect two pigments-blue-green biliverdin and red-brown protoporphyrin-in the eggs of a 70-million-year-old parrot-beaked oviraptorosaur called Heyuannia from China. Birds did not evolve their egg colors on their own, but inherited the ability from non-avian dinosaurs. Recently, the same pigments found in colored bird eggs have been discovered in some fossil dinosaur eggs. Eggshell theories were "kind of all over the place", said study author Mark Norell, a paleontologist at the American Museum of Natural History in NY.
People who are accustomed to see the eggs alone the hen, it is hard to imagine how diverse is their colouring from other birds, from chocolate brown to emerald green, from brick red to bright blue. Maps of protoporphyrin accumulation across the surface of numerous eggs, including Deinonychus and some troodontids revealed darker speckling patterns on top of the background color. For years, biologists and other scientists thought these patterns were a relatively recent evolutionary trait developed by modern birds, but new research into dinosaur eggs has revealed that some were just as colorful and unique as the ones we see today.
This is also what Wiemann hopes to research next-which theropods had colored eggs and which didn't, and how bird nests correspond to egg color. "A robin's egg is uniformly blue, but a quail's is spotted and speckled". Crocodiles and turtles bury their white eggs, which means they don't need to be camouflaged. A relative of Velociraptor called Deinonychus laid eggs with blue-green color; the lightly built carnivorous troodontids had eggshells of blue-green, beige, or white; and the eggs of the Chinese oviraptorosaur Heyuannia previously tested were deep blue-green.
The evolutionary link between dinosaurs and birds has been recognised for centuries but ornithologists long believed that birds evolved their coloured eggs several times over history, mimicking local hues to help their eggs blend in.
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But why? Wiemann and Norell both hypothesized that the emergence of egg color stemmed from theropods no longer laying their eggs in underground or covered nests.
Traditionally, dinosaurs were thought of as reptilian-style breeders that dumped their eggs and left. Stem birds, she said, were on the way toward what is considered modern birds and had "mixed characteristics", like teeth.
"This completely changes our understanding of how egg colors evolved", said the study's lead author, Yale paleontologist Jasmina Wiemann.
They found traces of pigments in the eggshells of all dinosaurs in the Maniraptora - a clade of small, bipedal, often feathered non-avian dinosaurs generally regarded as the ancestors of birds. Given the analytical methods from other scientific disciplines now available for work on fossils, "It's an fantastic time to be a paleontologist", she says.