No matter how much evidence we have that birds evolved from dinosaurs, it can still be hard to believe that the harmless little sparrow hopping about your park bench is somehow related to the mighty and ferocious Tyrannosaurus rex. But go far enough back, and there is a connection.
Now, a new finding further links modern avians and their ancient ancestors. In a paper published last week in Nature, a group of researchers from Yale University, the American Museum of Natural History, and the University of Bonn in Germany found that the coloration of bird eggshells evolved from dinosaurs, not, as previously believed, as an independent trait.
From the striking azure of an American Robin’s egg to the Jackson Pollock-esque brown squiggles on a Great Bowerbird’s, the diversity of colors and patterns in modern bird eggs derive from just two pigments: red and blue, or red-brown protoporphyrin IX and blue-green biliverdin. Birds have long been considered unique for their colored shells, but as it turns out, those same exact pigments can be found in the eggs of certain dinosaurs.
Analyzing 18 fossilized dinosaur eggshells from around the world, the researchers used Raman microspectroscopy, a nondestructive laser method, to test for the presence of the two pigments. They found them in the eggshells of Eumaniraptoran dinosaurs, a group including theropods such as velociraptors that are believed to have eventually evolved into modern birds.
The analysis also found that eggs belonging to dinosaurs that buried their eggs had no pigment at all. This, the researchers say, indicates that egg coloration might have co-evolved with the open-nesting habits of theropods.