Fossil Analysis Shows Mammalian Ancestors Laid Hard-Shelled Eggs 250 Million Years Ago

Egg Fossil Analysis of a fossil in South Africa proves that mammalian ancestors laid eggs 250 million years ago.

The fossil was found in Oviston, South Africa, in 2008 by a paleontologist. The fossilized egg and embryo belonged to a species called Lystrosaurus, a therapsid that is a forefather to modern-day mammals, including humans. The analysis is detailed in a study published in the journal Plos One.

A researcher stated that this marked the first time researchers could say with confidence that mammal ancestors like Lystrosaurus laid eggs. Therapsids were first described over 150 years ago based on fossils found in South Africa. Lystrosaurus was a pig-like herbivore with a turtle-like beak, naked skin, and two tusks.

The fossil contained a curled-up embryo tightly nestled in its soft, leathery eggshell.

The X-ray analysis showed that the Lystrosaurus embryo's beak had not fused together. Lystrosaurus eggs were unusually large for their body size. The large eggs indicated that Lystrosaurus babies were weaned on yolk instead of milk.

The eggs were less prone to desiccation because they lost less water through the leathery egg. The large eggs suggest that Lystrosaurus hatched at an advanced stage of development. There are two species of egg-laying mammals today: the duck-billed platypus and the echidna or spiny anteater.

Permian Extinction Around 252 million years ago, 90% of life on Earth died due to volcanic eruptions.

The volcanic eruptions acidified the ocean and released tons of carbon dioxide into the atmosphere. The event is known as the Great Dying. The fossil dates to 250 million years ago, shortly after the Great Dying.

Therapsids, including Lystrosaurus, survived this mass extinction. The discovery provides insight into early mammalian reproduction during a period of global upheaval.