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Arrangement of oviraptor-like eggs in an oviraptorid nest arrangement
Jasmina Wiemann / Yale University
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Jasmina Wiemann / Yale University
Assortment of paleognath and neognath bird eggs and a fossil theropod egg (right).
Jasmina Wiemann / Yale University
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Jasmina Wiemann / Yale University
Assortment of paleognath and neognath bird eggs and a fossil theropod egg (right).
Jasmina Wiemann / Yale University
The rainbow of hues seen in a modern bird eggs probably evolved in birds' dinosaur ancestors, which had eggs with colorful and speckled shells.
This is a new study of fossil eggs in the journal Nature. Researchers found that birds' close dinosaur related to eggs with traces of two pigments-a red-brown one and a blue-green one. This same pair of pigments mixes and matches in today's bird's eggs to produce colors ranging from robin's egg blue to red to yellow to green.
"There is a lot of diversity in this issue, which is unique to our modern birds," says Jasmina Wiemann, a paleontologist at Yale University. She says that it is based on the fact that birds' closest relative living, the crocodiles, "have completely uncolored, unpigmented eggs."
To see if colored eggs can actually go further back in history, she and her colleagues started by looking at the eggs of oviraptors– a relative of the velociraptor made famous in the movie Jurassic Park.
"This dinosaur is particularly interesting because of the first dinosaurs that have been built," she says, "explaining that earlier dinosaurs buried underground eggs, where color would not be expected to make any difference.
"Once you start to build an open nest, your eggs are exposed to the environment," she notes. Out there, colors and patterns could provide camouflage or help dinosaurs recognize their own eggs.
Inside some 66-million-year-old oviraptor egg fossils, her team found small concentrations of both pigments that color modern bird eggs. That was intriguing. Still, it was just one dinosaur.
Now the researchers have analyzed eggs shells from more. "We tried to cover the major branches of dinosaurs to get a good idea for all non-avian dinosaurs," she says.
They found no pigments in birds' relative relative dinosaurs, such as the groups that include triceratops and the long-necked diplodocus.
The red-brown and blue-green pigments were present, however, in eggshells from the group of dinosaurs that includes birds and their close relative. These pigments were built into the shells in the same way that they are in modern birds' eggs – and Wiemann thinks this can not be a coincidence.
"We have, very likely, a single evolutionary origin of egg color," she says.
What's more, the analysis of pigments showed that dinosaur eggs even had spots and speckles. And that surprised Mark Hauber, an ornithologist and expert on eggs at the University of Illinois, Urbana-Champaign.
"We are only now that dinosaur eggs were colorful, but they were speckled, which is a different aspect of diversity," Hauber says.
Dinosaurs may have needed these fancy eggs for the same reasons as birds, suggesting that their behavior could have been just as complex.
"Dinosaur eggs could have been camouflaged, they could have been found recognized, they could have been mimetic," says Hauber. "So there are all the things we do not have to consider for dinosaur eggs."
More, says Hauber, perhaps distinctive colors and markings are related to some of the dinosaur business we have not even thought of. A certain egg color might have warned would-be predators of danger, he says, "and that could be that the mama dinosaur comes back, or daddy dinosaur comes back, and will beat you up."
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