Were Dinosaur Eggs Colorful?

What could be more festive than a big bowl of Mini Eggs at Easter? Brown, white, green, and speckled, they reflect the diversity of egg décor we see in nature, but how far back do pretty eggs go? Were dinosaur eggs colorful?

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A 2017 study revealed that – yes – dinosaur eggs were colorful and we’ve found examples that date back 150 million years. This was quite a pivotal moment for ornithologists as it had been previously assumed that colorful eggs evolved much later in modern birds.

Reptiles like crocodiles lay pure white eggs and the general consensus was that the eggs of early birds would’ve been white, too. Today, they're the only animals known to lay colorful eggs, but were they the first? Not so, said the blue-green eggs of a 70-million-year-old oviraptor called Heyuannia huangi.

H. Huangi was among 15 Cretaceous-era dinosaurs and extinct birds represented in a stash of ancient eggshell fragments analyzed in that 2017 study. Using Raman microspectroscopy, scientists bounced lasers off the shell fragments’ surfaces to see what it revealed about their molecular makeup.

“I was originally taught that all the weird colors you can get in fossils, like the blueish-green hue, may be due to mineral precipitation,” said study author Jasmina Wiemann to National Geographic. “We screened through lots of eggshells, and one day had a positive result for these oviraptor eggs. It was a huge surprise. I couldn’t believe it.”

The results revealed a wide array of fossil egg colors and speckle patterns. Deinonychus and troodontid eggs were blue-green, like Heyuannia, and some had dark speckles layered on top. This may have been a protective adaptation, acting as a kind of camouflage that made it harder for passing predators to spot a free lunch.

“Egg camouflage represents a major character of open-nesting birds which accomplish protection of their unhatched offspring against visually oriented predators by cryptic egg coloration,” wrote the authors. “Cryptic coloration evolved to match the predominant shades of color found in the nesting environment.”

As well as identifying egg fragments’ coloration, we’ve also recently developed a new way to estimate the “burial age” of dinosaur eggshells. The novel approach is called LA-ICP-MS U-Pb calcite dating and it, too, involves firing lasers at eggs. This time, to measure tiny amounts of uranium and lead inside the samples.

The laser blasts remove a tiny amount of the surface that then goes into a mass spectrometer for analysis. We know uranium slowly turns into lead over time, so by measuring their ratios, we can figure out how long that sample has been decaying for, and hey presto – dinosaur eggshell burial age.

These novel methodologies mean that dinosaur eggs, once hard to read, can now give us all kinds of information, not just about the shell itself, but also the environment it was in. A Kinder Surprise for the ages.