This Fossil Egg is the First Found in Antarctica, and It May Have Belonged to a Mosasaur

In 2011, Chilean scientists discovered a football-sized fossil off the coast of Seymour Island, near the northern tip of the Antarctic Peninsula. Though they didn’t know what it was at the time—and simply called it “The Thing”—new research shows that not only is it the first fossil egg ever found in Antarctica, it’s also the largest soft-shelled egg ever found anywhere. In a study published today in the science journal Nature, researchers from the University of Texas at Austin and the University of Chile dated the nearshore rock formation where the fossil egg was found to be from the Late Cretaceous period—about 68 million years ago—and measured the fossil itself to be roughly 11.4 inches by 7.9 inches (29 centimeters by 20 centimeters). This empty, partially collapsed egg is smaller only than that of the elephant bird, an extinct, flightless species from Madagascar whose eggs averaged about 12 inches by 8 inches.

But beyond their size, the eggs don’t have much in common; an elephant bird egg is about five times thicker than this fossil egg, and its hard shell has distinct pores and a prismatic layer that the fossil egg lacks. In other words, an elephant bird egg resembles a giant chicken egg. (Andgiantis no exaggeration—an elephant bird egg could hold the contents of about 150 chicken eggs.)

With its soft shell and oblong shape, the new fossil egg, from the new taxon

Antarcticoolithus bradyi, is more similar to a lizard or snake egg, which suggests it could’ve been laid by a large reptile. To test that theory, the researchers compared it to the egg traits of 259 species of lepidosaurs—asubclassof reptile that includes snakes and lizards—and surmised that the egg-layer may have been a marine reptile that measured roughly 23 feet (7 meters) or longer. Read the free article.