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As any child can tell you, dinosaurs, not birds, have invented feathers. According to a new scientific report, dinosaurs have also invented – or, if you want to be technical, have evolved first – eggs of different colors. The birds do not develop the color of their eggs themselves, but inherit the abilities of non-avian dinosaurs.
A few years ago, the color of dinosaur eggs was unknown. Other reptiles, such as snakes and turtles, usually lay whitish eggs. Then, in 2015, Jasmina Wiemann and her colleagues reported the presence of two pigments, one blue-green and the other red, in oviraptor eggs.
But it was a dinosaur. Ms. Wiemann, a graduate student from Yale University, then worked with Mark Norell, a paleontologist from American Museum of Natural History, develop a non-destructive method of identifying pigments. They tested fossil eggshells from 14 different dinosaurs and also ancient and modern birds.
In the new report released Wednesday in Nature, they found a red-brown pigment called protoporphyrin IX and a blue-green pigment called biliverdine5 in modern birds and in a group of dinosaurs ancestors of modern birds – Eumaniraptorans, including favorites like velociraptor . They have also been found at the same depths from the surface in the modern and ancient bird shells and non-avian dinosaurs.
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They revealed the different substances contained in the eggs by shooting them lasers. They have developed a way to use this technique, known as Raman spectroscopy, to select pigments from other molecules.
"We can identify pigments by fingerprint," said Wiemann.
Darla Zelenitsky, a dinosaur paleontologist at the University of Calgary, said the combination of the new technology and the method Ms. Wiemann and Dr. Norell worked on had allowed them to show "that there was only evolutionary origin of the color of the egg ".
And, she said, "This is an example of another feature that has been considered exclusive among birds."
Egg-colored dinosaurs were species that kept their eggs in exposed nests: animals such as Deinonychus and some Troodontidae, active predators that may have nested in small groups but not in large nesting areas like some beaked dinosaurs duck.
The fossilized egg shells of duck beaks and other dinosaurs covering their mud eggs did not have any pigment.
The pigmented eggshells also had mottled patterns. There is evidence in modern birds that they help them to distinguish their own eggs, particularly so-called nesting pests, such as cuckoo, that nest in other birds' nests.
Much remains to be done to determine to what extent the color of the egg can be found in dinosaurs. And the presence of spots is likely to cause parasites in the nest well before the appearance of birds – the cuckoo dinosaur.
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