When faced with the hardship of frigid weather, some animals have a built-in survival mode: sleep.
Hibernation-like behavior in the Antarctic Circle may date back 250 million years, new fossil records show, predating the evolution of mammals and dinosaurs.
The evidence comes in the form of a curious “pre-mammal,” the Lystrosaurus.
Lystrosaurus was a genus of therapsids, animals distantly related to mammals. Most Lystrosauruses were the size of pigs, but they could get bigger — up to 8 feet long — and foraged for plants. The extraordinarily Pokemon-like creatures had squat frames, turtle-like beaks, and tusks that grew continuously.
Those tusks were crucial in helping researchers determine whether Lystrosaurus spent time in torpor, a hibernation-like state of deep sleep. These toothy protrusion provided hard evidence of the stress that comes with weathering cold, hard times.
Scientists took thin cross-sections of tusks from six Lystrosaurus discovered in Antarctica. They analyzed the fossils to measure the animals’ growth and stress during its lifetime.
Rings on the animals’ tusks were deposited as the tusks grew. Distinct patterns indicated long periods of stress associated with torpor: The rings were thick and closely spaced, for instance.
It’s the earliest known evidence of torpor, a state which involves an organism lowering its metabolism. The adaptation helps polar fauna survive when days are dark and cold, and food supply is limited.
With the Lystrosaurus sample, scientists are closer to understanding Antarctic life during the Early Triassic. The findings suggest that long before humans were around, animals were figuring out sleepy ways to deal with a harsh climate.
The study was published Thursday in the journal Communications Biology.