Scientists Discover 68-Million-Year-Old Giant Fossil Egg in Antarctica

Scientists have discovered a giant fossil egg, approximately 68 million years old, in Antarctica that provides new insights into how ancient reptiles reproduced during the dinosaur era. The discovery reveals that some giant sea reptiles likely laid eggs rather than giving birth directly.

The fossil egg, nicknamed “The Thing” by researchers because of its unusual shape, was found on Seymour Island, Antarctica. The egg measures approximately 11 inches (28 cm) in length and 8 inches (20 cm) in width. At these dimensions, the fossil is recorded as the largest soft-shelled egg ever discovered and the second-largest egg known from any ancient animal species.

When first discovered, the fossil did not appear to be an egg at all. The object looked like a soft, folded mass buried in sediment, leading researchers to initially believe it resembled a deflated pouch. However, upon microscopic examination, scientists discovered that the fossil had extremely thin walls, only a fraction of a millimetre thick, with no visible pores. Instead, its interior showed stacked thin layers, making its texture more similar to modern lizard or snake eggs than to the hard-shelled dinosaur eggs typically found.

The research was led by palaeontologist Lucas Legendre from the University of Texas at Austin, who studies the evolution of fossil eggs and the reproductive systems of ancient reptiles. The team assigned the scientific name Antarcticoolithus bradyi to the fossil. Based on their reconstruction, they concluded that the egg shell likely collapsed after hatching, which is why the fossil now appears like an empty, deflated pouch.

Prior to this discovery, scientists generally believed that large sea reptiles such as mosasaurus gave birth directly, like mammals, in the sea. This view emerged from previous research that found skulls of baby mosasaurus in open marine rocks, suggesting these animals could reproduce without needing to reach land.

However, this egg discovery has changed that perspective. Its thin and flexible shell indicates that some sea reptiles may have employed mixed reproductive strategies. In this strategy, the mother likely retained the embryo until nearly ready to hatch, then released a soft-shelled egg that hatched immediately in water.

At the same location where the egg was found, researchers also discovered bone fragments from Kaikaifilu hervei, one of the large mosasaurus species that lived in the region. This animal is estimated to have measured approximately 33 feet (10 metres) in length, making it one of the largest apex predators in Antarctic waters at that time.

Based on comparisons with 259 modern reptile species, scientists estimate that the mother of the egg was more than 23 feet in length. This size falls within the typical body range of mosasaurus. The size compatibility and the proximity of the fossil location make Kaikaifilu hervei a strong candidate as the animal that possibly laid the egg, although the connection cannot yet be definitively established.

Additionally, the same region contains fossils of juvenile mosasaurus and plesiosaur bones. Plesiosaurs were long-necked sea reptiles with flippers. This suggests that the area likely functioned as a nursery for young sea reptiles.

For several decades, almost all fossil eggs from dinosaurs and ancient reptiles that were discovered had hard, mineral-rich shells. This led scientists to believe that hard-shelled eggs represented an early form of dinosaur eggs. However, recent research shows a different picture.

Analysis of herbivorous dinosaur eggs, such as those from Protoceratops and Maussaurus, reveals that their eggs actually had soft and flexible shells, not hard ones like bird eggs. These findings suggest that soft-shelled eggs likely existed since early dinosaurs, whilst hard shells developed separately in some lineages.

This Antarctic egg discovery further expands that understanding, as it demonstrates that giant sea reptiles living near the poles also likely laid eggs with soft shells. Soft-shelled eggs are rarely preserved as fossils because they are easily destroyed by bacteria or predators. This fossil was able to survive because it was likely quickly buried under layers of mud and sand in shallow seas, protecting it from damage.

During that period, Antarctica had a warmer climate and ice-free coastlines, with seas rich in life. The stable sediment environment made the seabed around Seymour Island capable of preserving delicate organic remains for millions of years.

This discovery provides important insights into how early giant sea reptile life began, whilst also helping scientists understand the relationship between egg type, reproductive behaviour, and the environmental conditions in which ancient animals lived.