June 17 (UPI) -- Nearly a decade ago, Chilean scientists recovered what looked like a deflated football among ancient marine deposits of the Antarctic coast.
But until recently, the fossilized orb -- nicknamed "The Thing" -- sat unnamed in collections at Chile's National Museum of Natural History. New research, published Wednesday in the journal Nature, suggests The Thing is actually a 66-million-year-old egg.
Measuring 11 inches in length and 7 inches wide, it is the largest soft shell egg ever found, and the second largest in history. The biggest egg ever discovered was laid by an elephant bird, a kiwi relative that went extinct only a few thousand years ago.
Scientists hypothesized that the egg found in Antarctica was laid by an extinct, giant marine reptile, like a mosasaur.
"It is from an animal the size of a large dinosaur, but it is completely unlike a dinosaur egg," lead study author Lucas Legendre, geoscientist and postdoctoral researcher at the University of Texas, said in a news release. "It is most similar to the eggs of lizards and snakes, but it is from a truly giant relative of these animals."
Chilean scientist David Rubilar-Rogers, a member of the research team that first found the egg, showed the fossil to scientists visiting the museum where it was stored, but most were puzzled -- that is until Julia Clarke, a professor of geological sciences at Texas, took a look.
"I showed it to her and, after a few minutes, Julia told me it could be a deflated egg!" Rubilar-Rogers said.
Clarke's hunch was confirmed when powerful microscopes revealed several layers of membrane beneath the surface of the egg. According to Rubilar-Rogers, the ancient egg looks a lot like transparent, quick-hatching eggs laid by several modern snake and lizard species.
By analyzing the body and egg sizes of 259 living reptiles, researchers determined the species that laid the deflated football some 66 million years ago would have likely stretched about 20 feet from the nose to the end of the body, not counting the tail.
Marine deposits near the egg's origin have previously yielded the remains of mosasaurs and plesiosaurs, both babies and adults.
"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," Legendre said.
It's possible the ancient marine lizard laid eggs in the open sea like some modern sea snakes. The reptile could have also buried its eggs on the beach, just beyond the breakers.
"We can't exclude the idea that they shoved their tail end up on shore because nothing like this has ever been discovered," Clarke said.