The light blue of a robin egg isn’t just pretty to look at, as it’s also a unique form of camouflage. Eggshells with colors and speckles are only found with birds that have partially or fully exposed nests.
It had been thought that eggshell color was a modern evolutionary adaptation, but a new study shows that it’s a trait that links all the way back to the dinosaurs.
The results, published in the journal Nature, shed light on how the blue and red pigments found in many bird eggs today developed out of necessity when dinosaurs first started laying their eggs in open nests.
“This completely changes our understanding of how egg colors evolved,” said Jasmina Wiemann, the study’s lead author. “For two centuries, ornithologists assumed that egg color appeared in modern birds’ eggs multiple times, independently.”
Eggshells today only use two pigments, red and blue, to create the various spots, speckles, and hues we instantly associate with some species of birds.
The researchers examined 18 fossil dinosaur eggshells to see if there were any traces of these pigments.
Using laser microspectroscopy, the team was able to test the egg-shells for different pigments non-invasively.
Red and blue pigments were found in eggshells that belonged to the Eumaniraptoran dinosaurs like the velociraptor.
Oviraptors, a relative of the velociraptor, were the first known dinosaurs to lay their eggs in open nests and so it makes sense that eggshell pigment would be found in their family tree.
“We infer that egg color co-evolved with open nesting habits in dinosaurs,” said Wiemann. “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.”
Image Credit: Jasmina Wiemann/Yale University