Large Soft-Shelled Egg Fossil Identified

[Recusant]

This fossil was a "what is it?" for years, but in a paper published in Nature, paleontologists describe evidence indicating it's a very large egg that had a soft shell. The story linked below also describes a study published in the same issue of Nature that advances the theory that dinosaur eggs were originally mostly soft-shelled.

"We Finally Know What The Huge 'Thing' Fossil From Antarctica Actually Is" | ScienceAlert

Image Credit: Chilean National Museum of Natural History/Cristian Becker

Scientists had nicknamed it "The Thing" – a mysterious football-sized fossil discovered in Antarctica that sat in a Chilean museum awaiting someone who could work out just what it was.

Now, analysis has revealed that the mystery fossil is in fact a soft-shelled egg, the largest ever found, laid some 68 million years ago, possibly by a type of extinct sea snake or lizard.

The revelation ends nearly a decade of speculation about the fossil, and could change thinking about the lives of marine creatures in this era, said Lucas Legendre, lead author of a paper detailing the findings, published Wednesday in the journal Nature.

"It is very rare to find fossil soft-shelled eggs that are that well-preserved," Legendre, a post-doctoral fellow at the University of Texas at Austin, told AFP [Agence France-Presse].

"This new egg is by far the largest soft-shelled egg ever discovered. We did not know that these eggs could reach such an enormous size, and since we hypothesise it was laid by a giant marine reptile, it might also be a unique glimpse into the reproductive strategy of these animals," he said.

[. . .]

The paper was published in Nature along a separate study that argues that it wasn't only ancient reptiles that laid soft-shell eggs – dinosaurs did too.

For many years, experts have believed dinosaurs only laid hard-shelled eggs, based on those found in the fossil record.

But Mark Norell, curator of paleontology at the American Museum of Natural History, said the discovery of a group of fossilised embryonic Protoceratops dinosaurs in Mongolia made him revisit the assumption.

"Why do we only find dinosaur eggs relatively late in the Mesozoic and why only in a couple groups of dinosaurs," he said he asked himself.

"And why have we not found ceratopsian egg shells, since ceratopsian dinosaurs are the most common animals at many sites in Asia and North America, which preserve dinosaur eggs?"

The answer, he theorised, was that early dinosaurs laid soft-shell eggs that were destroyed and not fossilised.

To test the theory, Norell and a team analysed the material around some of the Protoceratops skeletons in the fossil and another fossil of two apparently newborn Mussaurus.

They found chemical signatures showing the dinosaurs would have been surrounded by soft, leathery eggshells.

"The first dinosaur egg was soft-shelled," Norell and his team conclude in the paper.

[Link to full article.]

Both papers are behind the Nature paywall, but there are links to the abstracts in the article.