Soft-shelled dinosaur eggs crack the mystery of missing fossils


Like contemporary reptiles, some dinosaurs may have hatched from soft-shelled eggs.

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Despite what movies like Jurassic Park and The Land Before Time may lead you to believe, some dinosaurs may not have cracked hard-boiled eggs when they first appeared in the world. Instead, they may have had a much milder start.

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

“The assumption has always been that the ancestral dinosaur egg was a hard shell,” said Mark Norell, paleontologist at the American Museum of Natural History and lead author of one of the studies, in a press release. The previous eggs in the fossil record come mainly from the end of the dinosaur timeline, closer to their ultimate end about 66 million years ago. We have fossilized bones of creatures from 240 million years ago, but no eggs.

“We found thousands of skeletal remains of ceratopsian dinosaurs, but almost none of their eggs. So why were their eggs not kept?” Norell asks.

Norell believes his team answered this question in their study findings, despite the speculation that dinosaurs produce hard-shell eggs, there is fossilized evidence confirming certain types of dinosaurs, namely: Protoceratops and Mussaurus, produced soft-shelled eggs. The creatures buried and incubated these eggs in moist soil, as some reptiles do today. Soft-shelled eggs are not as deliciously preserved as their hard-shelled counterparts – they disintegrate before being able to fossilize – leaving a gap in the fossil record.

Now this gap can be filled.

A second study provided additional evidence, examining a soft-shelled egg found in Antarctica, which has since been dated to around 66 million years ago. It is the first fossilized egg ever found in Antarctica – which was much less cold than today.

However, the scientists responsible for the discovery are not sure of the mother of the egg. Without any embryonic remains in the bud, it is impossible to say who it belonged to.

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

Together, the studies reassess the theory that all dinosaurs laid calcified hard-boiled eggs – like their descendants of chicken – and instead, the dinosaurs may have been more similar to reptiles.

There is no doubt that the shells have evolved over time to move more towards hard than soft shells. But since there are so few soft-shelled eggs in the fossil record, it is difficult to determine a solid evolutionary chronology. Finding an answer comes down to the time of laying and the species of dinosaur in question.

Reading in progress:
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Feathered dinosaur tail found preserved in amber


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