First-ever fossil egg in Antarctica laid by massive reptile

A mysterious fossil that was recovered nine years ago has turned out to be the largest soft-shell egg ever discovered, as well as the first fossilized egg ever found in Antarctica.

The egg was discovered by a team of Chilean scientists in 2011. Resembling a deflated football, the egg sat unidentified and unlabeled in Chile’s National Museum of Natural History. The unusual specimen was known only by its movie-inspired nickname “The Thing.”

A recent analysis led by researchers at the University of Texas at Austin has revealed that the giant egg, which measures more than 11 by 7 inches, was laid by a dinosaur-sized relative of snakes and reptiles about 66 million years old. 

The findings are particularly significant because scientists thought that the large marine reptiles of this time, such as mosasaurs, gave birth to live offspring rather than laying eggs. 

“It is from an animal the size of a large dinosaur, but it is completely unlike a dinosaur egg,” said study lead author Lucas Legendre. “It is most similar to the eggs of lizards and snakes, but it is from a truly giant relative of these animals.”

Study co-author David Rubilar-Rogers of Chile’s National Museum of Natural History was one of the scientists who discovered the fossil in 2011. He asked various experts to take a look at the specimen, but its origin remained unknown for years. 

When Professor Julia Clarke visited the museum in 2018, she theorized that the mysterious fossil may be a deflated soft-shell egg. 

Back in the lab, Legendre used a variety of microscopes to confirm the egg’s identity in several layers of membrane. Legendre said the structure is very similar to transparent, quick-hatching eggs laid by some snakes and lizards today. 

Since the fossil egg had hatched and contained no skeleton, Legendre investigated by compiling a dataset to compare the body size of 259 living reptiles to the size of their eggs. He determined that the fossil egg belonged to a creature with a body that was more than 20 feet long, not even counting a tail. 

The egg was found in an Antarctic site that also contained skeletons from baby mosasaurs and plesiosaurs, along with adult specimens. 

“Many authors have hypothesized that this was sort of a nursery site with shallow protected water, a cove environment where the young ones would have had a quiet setting to grow up,” said Legendre.

The scientists have some ideas as to how the massive reptile may have managed to lay the eggs – in the open water like some sea snakes or on a beach like sea turtles. 

The researchers said that laying the eggs on the beach would require some fancy maneuvering. The reptile would have had to wriggle its tail onshore while staying mostly submerged and supported by water.

“We can’t exclude the idea that they shoved their tail end up on shore because nothing like this has ever been discovered,” said Professor Clarke.

The study is published in the journal Nature.

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By Chrissy Sexton, Earth.com Staff Writer