Thursday, 22 November, 2018

Birds Got Their Colorful, Speckled Eggs From Dinosaurs

Assortment of paleognath and neognath bird eggs and a fossil theropod egg View Slideshow Assortment of paleognath and neognath bird eggs and a fossil theropod egg. Jasmina Wiemann Yale University
Sandy Nunez | 02 November, 2018, 23:19

Modern birds use only two pigments, red and blue, to create all of the various egg colors, spots, and speckles.

According to ornithologist Mark Hauber: "We not only know now that dinosaur eggs were colorful, but they were speckled, which is a whole other aspect of diversity.Dinosaur eggs could have been camouflaged, they could have been individually recognized, they could have been mimetic".

Birds, unusual as it seems, are living dinosaurs, the last of a lineage that otherwise went extinct 66 million years ago.

"Some were uniformly coloured", said paleontologist and study co-author Mark Norell of the American Museum of Natural History in NY. They are red-brown protoporphyrin IX and blue-green biliverdin, which also have been found in theropod eggs. Maps of protoporphyrin accumulation across the surface of numerous eggs, including Deinonychus and some troodontids revealed darker speckling patterns on top of the background color.

Not only were dinosaurs the masters of the land and the sea, but they were also the masters of color, a new study shows. They discovered this by slicing off a piece of a dinosaur egg and putting it through a molecule-identifying mass spectrometer machine.

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.

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If you're interested in all the practical advantages of speckled and brightly colored eggs, check out this article. The method requires no destruction of fossils, instead bouncing a laser off the surface of the eggshells to betray their molecular makeup, including whether they carried traces of the two pigments known to color modern eggshells. A relative of Velociraptor called Deinonychus laid eggs with blue-green color; the lightly built carnivorous troodontids had eggshells of blue-green, beige, or white; and the eggs of the Chinese oviraptorosaur Heyuannia previously tested were deep blue-green.

"This completely changes our understanding of how egg colors evolved", said Jasmina Wiemann, Yale paleontologist and the study's lead author. The biliverdin was able to find in the remains of eggs of seven different dinosaurs.

Different nesting environments, as well as nesting behaviors, are thought to influence egg color.

But, once again, birds are living dinosaurs. Birds with white eggs today, such as ostriches, parrots, and some domestic chickens, must have later lost the trait of coloring their eggs through evolution, she says.

"We infer that egg color co-evolved with open nesting habits in dinosaurs", Wiemann said. Other scientists told her she was "wasting her time", she said, because they assumed dinosaur eggs lacked pigment.

But why? Wiemann and Norell both hypothesized that the emergence of egg color stemmed from theropods no longer laying their eggs in underground or covered nests. Given the analytical methods from other scientific disciplines now available for work on fossils, "It's an wonderful time to be a paleontologist", she says.