If you come across a bird nest there’s usually a pretty good way of telling what kind of feathered friend was responsible for it, even if the bird itself isn’t around. The color, size, and pattern of a bird’s eggs is often unique to its species, and there’s online tools and even entire books dedicated to classifying bird eggs so that bird watchers can easily identify them. But why does such a wide range of colors and patterns exist in the first place?

In a new study published in Nature, scientists from Yale as well as the American Museum of Natural History and the University of Bonn explain that birds didn’t develop colored eggs all on their own. No, it seems egg color is something that was passed down over millions of years from dinosaurs.

At this point, the idea that birds are actually just what’s left of dinosaurs is widely accepted, so it should be no surprise that researchers are working hard to determine what pieces of modern birds are actually leftovers from much more ferocious beasts that roamed the earth tens of millions of years back.

The researchers in this particular study looked closely at various fossilized eggs from dinosaurs to see if they could detect what was once pigment. They discovered that some branches of the dinosaur tree had no pigment on their eggs, including sauropods and many other large, four-legged species. However, many theropod dinosaurs, which walked on their hind legs and are thought to be the direct ancestors of modern birds, did indeed have color patterns as well as speckles and spots on their eggs.

“Birds were not the first [egg-layers] to produce coloured eggs,” the researchers write. “As with many other characteristics, this is an attribute that evolved deep within the dinosaur tree and long before the spectacular radiation of modern birds.”

The team found that the diversity of color and patterns on the eggs of some dinosaurs species matches up surprisingly well with that of modern birds. Additionally, the mechanisms by which the eggs received their color seems to be identical between birds we see today and dinosaurs from millions of years ago.

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