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According to a new study by Jasmina Wiemann, a researcher at Yale University, modern birds inherited the color of their eggs from non-avian ancestors of dinosaurs that lay in fully or partially open nests.
The colors found in modern bird eggs have not evolved independently, as previously thought, but rather evolved from dinosaurs. It is an artistic impression of the oviraptorid dinosaur Huanansaurus ganzhouensis. Image credit: Chuang Zhao.
"This completely changes our understanding of how egg colors have evolved," said Wiemann, a paleontologist in the Department of Geology and Geophysics at Yale University.
"For two centuries, ornithologists have badumed that the color of the egg appeared independently in the eggs of modern birds."
The color of the birds' eggs reflects the characteristic preferences of nesting environments and brooding behaviors.
Modern birds only use two pigments – the blue-green biliverdin and the red-brown protoporphyrin IX – to create all the colors, stains and spots of the egg.
Wiemann and his colleagues at the American Museum of Natural History and the Bonn University badyzed 18 samples of fossil dinosaur eggshells from around the world, using a non-destructive laser microspectroscopy to detect the presence of two eggshell pigments.
A dinosaur looking like a cbadowary named Beibeilong sinensis incubating eggs. Image credit: Zhao Chuang.
They found pigments in eggshells belonging to the Eumaniraptoran dinosaurs, among which are small carnivorous dinosaurs such as Velociraptor.
"We infer that the color of the egg has co-evolved with the open nesting habits of the dinosaurs," Wiemann explained.
"Once the dinosaurs began to build open nests, the exposure of eggs to visual hunter predators and even to nesting pests favored the evolution of camouflaging egg colors and hides. patterns of spots and flecks individually recognizable.
Color of the eggs of the archosaurs: the internal nodes are: (1) Archosauria, (2) Dinosauria, (3) Ornithischia, (4) Saurischia, (5) Eumaniraptora, (6) Paraves and (7) Aves; the egg icon in Eumaniraptora phylogeny labels. All species are represented by an icon indicating the shape of the egg and an example of reconstituted color. If shell pigments are present, the area below the spectral function is stained blue (biliverdin) or orange (protoporphyrin IX) and all pigment bands are marked with blue (biliverdin) or red ( protoporphyrin IX). The photographs show the nesting samples and icons encode three nesting strategies: buried (partially) open nesting and nesting open trees. UA – arbitrary units. Image credit: Wiemann et al, doi: 10.1038 / s41586-018-0646-5.
"Colorful eggs have been viewed as a unique feature of birds for over a century," said co-author Mark Norell, curator of paleontology at Macaulay at the American Museum of Natural History.
"Like feathers and triangles, we now know that the color of eggs has evolved in their predecessors, long before the appearance of birds."
The study is published in the journal Nature.
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Jasmina Wiemann et al. The color of the dinosaur egg had only one evolutionary origin. Nature, published online 31 October 2018; doi: 10.1038 / s41586-018-0646-5
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