Dinosaurs Had Colored Eggs, New Study Shows

Modern birds such as the American Robin and Common Tern lay colored eggs, a trait that first appeared in their dinosaur ancestors. 
© Jasmina Wiemann/Yale University

Feathers, wishbones, and hollow skeletons aren’t just bird traits. Modern paleontology tells us that birds are, in fact, dinosaurs, and that many “bird-like” characteristics actually extend back to animals that lived millions of years ago. Now, a new study by scientists at the Museum, Yale, and the University of Bonn adds one more item to the list of bird traits that first appeared in dinosaur ancestors: egg color.

“Colored eggs have been considered a unique bird characteristic for over a century,” said study co-author Mark Norell, the Museum’s Macaulay Curator of Paleontology. “We now know that egg color evolved in their dinosaur predecessors long before birds appeared.”

Among amniotes—a group of vertebrates that includes all mammals, birds, and reptiles whose eggs develop inside a protective membrane—birds are the only living animals with colored eggs. Ornithologists long assumed that this trait evolved independently and multiple times within the bird Tree of Life.

Two pigments, red (protoporphyrin) and blue (biliverdin), are responsible for creating all of the various egg colors, spots, and speckles we see in modern birds. To investigate whether egg color first appeared in dinosaurs, the research team, led by Yale paleontologist Jasmina Wiemann, analyzed 18 fossil dinosaur eggshell samples from around the world using a type of non-destructive laser scanning technique called Raman microspectroscopy to test for the presence of the pigments.

Egg color pigments have been found preserved in the eggshells of Deinonychus antirrhopus, a small theropod carnivore that lived during the early Cretaceous.
Jasmina Wiemann/Yale University

While the pigments were not found in eggshells of ornithischian or sauropod dinosaurs—groups that represent animals like Edmontosaurus and titanosaurs like Patagotitan— they were discovered in eggshells belonging to Eumaniraptoran dinosaurs, which include small, carnivorous animals such as Velociraptor and Deinonychus. In addition to the presence of pigmentation, the study also found that many eggs were also patterned.

“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 favored the evolution of camouflaging egg colors, and individually recognizable patterns of spots and speckles.”

The researchers’ findings appear today in the journal Nature.