The Great Speckled Dinosaur Egg
Posted October 31, 2018 7:04 p.m. EDT
As any child can tell you, dinosaurs, not birds, invented feathers. According to a new scientific report, dinosaurs also invented — or, if you want to get technical, first evolved — eggs of different colors. Birds did not evolve their egg colors on their own, but inherited the ability from non-avian dinosaurs.
Until a few years ago, the color of dinosaur eggs was unknown. Other reptiles, like snakes and turtles, usually lay off-white eggs. Then, in 2015, Jasmina Wiemann and colleagues reported the presence of two pigments, one blue-green and one red, in oviraptor eggs.
But that was one dinosaur. Wiemann, a graduate student at Yale University went on to work with Mark Norell, a paleontologist at the American Museum of Natural History, to develop a nondestructive method for identifying pigments. They tested fossilized eggshells from 14 different dinosaurs and also ancient and modern birds.
In the new report published Wednesday in Nature, they write that they found a red-brown pigment called protoporphyrin IX and a blue-green one called biliverdin5 in both modern birds and in a group of dinosaurs that were ancestors of modern birds — Eumaniraptorans, including favorites like velociraptor. They were also found at the same depths from the surface in the shells of modern and ancient birds and non-avian dinosaurs.
They revealed the different substances in the eggshells by firing lasers at them. They developed a way to use that technique, known as Raman spectroscopy, to pick out pigments from other molecules.
“We can fingerprint the pigments,” Wiemann said.
Darla Zelenitsky, a dinosaur paleontologist at the University of Calgary, said the combination of new technology and the method that Wiemann and Norell worked on allowed them to show “that there was a single evolutionary origin of egg color.”
And, she said, “It’s an example of another feature that was really thought to be exclusive among birds.”
The dinosaurs with egg color were species that kept their eggs in exposed nests: animals like Deinonychus and some Troodontids, active predators that may have laid nests in small groups but not in vast nesting grounds like some of the duck-billed dinosaurs.
Fossil eggshells from duckbills and other dinosaurs that covered their eggs with mud had no pigment.
The eggshells with pigment showed speckled patterns as well, and in modern birds there is some evidence that such patterns help birds distinguish their own eggs, particularly from nest parasites, like the cuckoo, that lay eggs in other birds’ nests.
There’s more work to be done to see how far back egg color can be traced among dinosaurs. And the presence of speckling raises the possibility there may have been nest parasites long before the appearance of birds — the cuckoo dinosaur.