Dinosaurs put all coloured birds' eggs in one basket, evolutionarily speaking

A new study says the colours found in modern birds' eggs did not evolve independently, as previously thought, but evolved instead from dinosaurs.

Fossil theropod dinosaur egg (front), with corvid eggs in a nest. Fossil Deinonychus
and oviraptor eggs were probably similar in colouration to corvid eggs
 [Credit: Jasmina Wiemann/Yale University]

According to researchers at Yale, the American Museum of Natural History, and the University of Bonn, birds inherited their egg colour from non-avian dinosaur ancestors that laid eggs in fully or partially open nests. The researchers' findings appear in the online edition of the journal Nature.

"This completely changes our understanding of how egg colours evolved," said the study's lead author, Yale paleontologist Jasmina Wiemann. "For two centuries, ornithologists assumed that egg colour appeared in modern birds' eggs multiple times, independently."

Illustration of a hatching Deinonychus chick from a blue egg with brown spots.
The diversity researchers recovered for dinosaur egg colours mirrors that
found for modern bird eggs [Credit: Jasmina Wiemann/Yale University]

The egg colours of birds reflect characteristic preferences in nesting environments and brooding behaviours. Modern birds use only two pigments, red and blue, to create all of the various egg colours, spots, and speckles.

Wiemann and her colleagues 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. They found them in eggshells belonging to Eumaniraptoran dinosaurs, which include small, carnivorous dinosaurs such as Velociraptor.

An assortment of paleognath and neognath bird eggs and a fossil theropod egg (on the right)
[Credit: Jasmina Wiemann/Yale University]

"We infer that egg color co-evolved with open nesting habits in dinosaurs," Wiemann said. "Once dinosaurs started to build open nests, exposure of the eggs to visually hunting predators and even nesting parasites favoured the evolution of camouflaging egg colors, and individually recognizable patterns of spots and speckles."

Co-author Mark Norell, the Macaulay Curator of Paleontology at the American Museum of Natural History, noted that "Coloured eggs have been considered a unique bird characteristic for over a century. Like feathers and wishbones, we now know that egg colour evolved in their dinosaur predecessors long before birds appeared."

Author: Jim Shelton | Source: Yale University [October 31, 2018]