Modern Birds Inherited Colored Eggs from Their Dinosaur Ancestors, Study Says

Exploring Prehistoric Life
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Saturday, November 3, 2018

The colors found in modern birds’ eggs did not evolve independently, as previously thought, but evolved instead from dinosaurs. This is an artist’s impression of the oviraptorid dinosaur Huanansaurus ganzhouensis. Image credit: Chuang Zhao.

Modern birds inherited their egg color from non-avian dinosaur ancestors that laid eggs in fully or partially open nests, according to new research led by Yale University researcher Jasmina Wiemann.

“This completely changes our understanding of how egg colors evolved,” said Wiemann, a paleontologist in the Department of Geology & Geophysics at Yale University.

“For two centuries, ornithologists assumed that egg color appeared in modern birds’ eggs multiple times, independently.”

The egg colors of birds reflect characteristic preferences in nesting environments and brooding behaviors.

Modern birds use only two pigments — blue-green biliverdin and red-brown protoporphyrin IX — to create all of the various egg colors, spots, and speckles.

Wiemann and her colleagues from the American Museum of Natural History and the University of Bonn analyzed 18 fossil dinosaur eggshell samples from around the world, using non-destructive laser microspectroscopy to test for the presence of the two eggshell pigments.

A nesting cassowary-like dinosaur named Beibeilong sinensis in the act of incubating eggs. Image credit: Zhao Chuang.

They found the pigments in eggshells belonging to Eumaniraptoran dinosaurs, which include small, carnivorous dinosaurs such as Velociraptor.

“We infer that egg color co-evolved with open nesting habits in dinosaurs,” Wiemann explained.

“Once dinosaurs started to build open nests, exposure of the eggs to visually hunting predators and even nesting parasites favored the evolution of camouflaging egg colors, and individually recognizable patterns of spots and speckles.”

Egg colors of archosaurs: the internal nodes are (1) Archosauria, (2) Dinosauria, (3) Ornithischia, (4) Saurischia, (5) Eumaniraptora, (6) Paraves and (7) Aves; the egg icon in the phylogeny labels Eumaniraptora. All species are represented by an icon indicating egg shape, and an example of reconstructed color. If eggshell pigments are present, the area below the spectral function is colored in blue (biliverdin) or orange (protoporphyrin IX), and all pigment bands are labeled with either blue (biliverdin) or red (protoporphyrin IX) dots. Photographs show the samples and nest icons encode three nesting strategies: buried, (partially) open ground and open tree nesting. AU – arbitrary units. Image credit: Wiemann et al, doi: 10.1038/s41586-018-0646-5.

“Colored eggs have been considered a unique bird characteristic for over a century,” said co-author Dr. Mark Norell, the Macaulay Curator of Paleontology at the American Museum of Natural History.

“Like feathers and wishbones, we now know that egg color evolved in their dinosaur predecessors long before birds appeared.”

The study is published in the journal Nature.

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Jasmina Wiemann et al. Dinosaur egg colour had a single evolutionary origin. Nature, published online October 31, 2018; doi: 10.1038/s41586-018-0646-5

Source: www.sci-news.com