Soft-shelled dinosaur eggs crack the mystery of missing fossils

Despite what movies like Jurassic Park and The Land Before Time may lead you to believe, some dinosaurs may not have cracked open hard-shelled eggs as they emerged into the world. Instead, they may have had a much softer debut.

According to two studies published in Nature this week, dinosaur eggs may have been, well… squishy. 

“The assumption has always been that the ancestral dinosaur egg was hard-shelled,” said Mark Norell, a paleontologist at the American Museum of Natural History and lead author on one of the studies, in a press release. Previous eggs in the fossil record mostly come from late in the dinosaur timeline, closer to their ultimate end some 66 million years ago. We’ve got fossilized bones of creatures dating back 240 million years, but no eggs. 

“We’ve found thousands of skeletal remains of ceratopsian dinosaurs, but almost none of their eggs. So why weren’t their eggs preserved?” Norell asks.

Norell believes his team have answered that question in their study finding, despite conjecture dinosaurs produce hard-shelled eggs, there is fossilized evidence confirming some types of dinosaur, namely, Protoceratops and Mussaurus, produced soft-shelled eggs. The creatures buried and incubated these eggs in moist soil, like some reptiles do today. Soft-shelled eggs aren’t as exquisitely preserved as their hard-shelled counterparts — they disintegrate before given a chance to fossilize — leaving a gap in the fossil record. 

Now, that gap may be filled.

A second study provided further evidence, examining a soft-shelled egg found in Antarctica, which has since been dated at approximately 66 million years old. It’s the first ever fossilized egg found in Antarctica — which was far less chilly than it is now. 

The scientists responsible for the discovery aren’t certain of the egg’s mother, however. Without any embryonic remains within the egg, it’s impossible to say who it belonged to. 

The team suggest it was likely laid by a dinosaur due to its estimated weight and its closeness to other discovered fossilized eggs belonging to non-avian dinosaurs. The egg itself is huge — the largest soft-shell ever found and second largest of all-time. The suspicion is it was something like a Mosasaur, a huge marine dinosaur that patrolled the oceans. 

Together, the studies re-evaluate the theory all dinosaurs laid calcified, hard-shelled eggs — like their chicken descendants — and instead postulate dinosaurs may have been more similar to reptiles.

There’s little doubt that the eggshells evolved over time to trend more toward hard shells than soft. But because there are so few soft-shelled eggs on the fossil record, it’s difficult to pin down a solid evolutionary timeline. Finding an answer comes down to the time the egg was laid and the species of the dinosaur in question.