What did dinosaur eggs look like?

By Victoria Jaggard, SCIENCE Executive Editor

One of my favorite family traditions growing up was celebrating Easter with cascarones. For the first few months of the year, I would watch with glee as my mom carefully cracked our weekend breakfast eggs to leave only a dime-size hole on one end, and I relished playing with the food dyes and confetti on assembly day. But of course, nothing compared to the satisfying crunch as I smashed one of those carefully made eggs over the head of a laughing aunt, uncle, or cousin on Easter morning.

Humans have a long history of weaving colorful bird eggs into our cultural traditions. And as with many things that bring me joy, I can thank dinosaurs for that.

Modern birds are the last living descendants of dinosaurs, which also laid eggs in a fabulous variety of shapes and colors. According to research on the fossilized pigments from ancient eggs, dinosaurs picked up the habit of making their shells in a rainbow of hues more than 145 million years ago. Perhaps counterintuitively to us, with our limited human perception of color, adding blues and greens and speckles to eggs was a way of making them less visible to predators, our Michael Greshko reported in 2018. That’s because calcite, the white mineral that makes up hard eggshells, would glow vivid pink to a dinosaur’s eyes.

But go back even further, and it seems dinosaur eggs didn’t need that extra layer of pigmented protection, because they were buried from view. According to a paper released this week in the journal Nature, fossil eggs from the dinosaurs Protoceratops and Mussaurus (pictured above) both show chemical traits of being soft rather than calcified. Placing these species on a dinosaur family tree and working backward, the researchers conclude that the common ancestor of all dinosaurs most likely filled its nests with soft, leathery eggs left buried in sand or soil, akin to the habits of modern sea turtles.

From that starting position, the team says, dinosaurs went on to develop hard eggshells three separate times during their evolutionary journey—including on the branch of the tree that gave rise to modern birds. So, thank you, dinosaurs for giving me the precious gift of terrifying my South Texas relatives with annual spatterings of colorful eggshell in their hair.

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The last glimpse

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