What's Lystrosaurus? Evidence of hibernation-like state found in tusked animal that existed before dinosaurs

The animal called Lystrosaurus roamed the Earth 250M years ago in the Early Triassic period and existed even before dinosaurs arrived


                            What's Lystrosaurus? Evidence of hibernation-like state found in tusked animal that existed before dinosaurs
Life restoration of Lystrosaurus (Crystal Shin)

An animal that survived a mass extinction about 250 billion years ago appears to have slipped into a hibernation-like state to cope with the harsh winter conditions in Antarctica. These are findings from a new study which suggests that the adaptation — seen in some modern animals — could date back to prehistoric times.

The prehistoric animal is Lystrosaurus, a far relative of mammals. They roamed the Earth 250M years ago in the Early Triassic period and existed even before dinosaurs arrived at the scene. According to researchers, these creatures were stubby and roughly pig-sized. However, some grew up to 6 to 8 feet. They had no teeth but had tusks in the upper jaw to support foraging.

When animals hibernate, they go into a deep-sleep state, they slow their breathing rates and lower their body temperatures. This adaptation allows them to stay put for days or even weeks, without having to need water and food. It helps them survive the cold and food scarcity. 

(Getty Images)

"Animals that live at or near the poles have always had to cope with the more extreme environments present there," said lead author Megan Whitney, a postdoctoral researcher at Harvard University. "These preliminary findings indicate that entering into a hibernation-like state is not a relatively new type of adaptation. It is an ancient one," Whitney, who conducted this study as a doctoral student at the University of Washington (UW), added. 

These creatures survived the Permian mass extinction, which wiped out 90% of the world's species, including 70% of the vertebrates. Following the event, Lystrosaurus likely spread across the world, from Russia to Antarctica. "The fact that Lystrosaurus survived the end-Permian mass extinction and had such a wide range in the early Triassic has made them a very well-studied group of animals for understanding survival and adaptation," said co-author Christian Sidor, a UW professor of biology.

In this study, Whitney examined and compared six Lystrosaurus fossils found in Antarctica with four in South Africa. They studied their tusks, which like elephants, grow with age. The fossilized tusks hold records on the animal's life-history, including metabolism, growth, and stress or strain. In the cross-section of the tusks, the team specifically looked at dentine, which is deposited as concentric circles. Dentine is a bony tissue present in human teeth as well, under the enamel.

This thin-section of the fossilized tusk from an Antarctic Lystrosaurus shows layers of dentine deposited in rings of growth. At the top right is a close-up view of the layers, with a white bar highlighting a zone indicative of a hibernation-like state. (Megan Whitney/Christian Sidor)

The analysis showed that the tusks of Antarctic Lystrosaurus and their South African counterparts showed similar growth patterns. But one difference stood out: the Antarctic fossils had closely-spaced, thick rings. This feature suggests less dentine deposition, which could be the result of prolonged stress associated with hibernation, according to the researchers. 

However, the team is not sure whether the animal went through true hibernation. Instead, they think the animal may have gone into a hibernation-like state, involving a more short-term reduction in metabolism. "Cold-blooded animals often shut down their metabolism entirely during a tough season, but many endothermic or 'warm-blooded' animals that hibernate frequently reactivate their metabolism during the hibernation period," said Whitney. "What we observed in the Antarctic Lystrosaurus tusks fits a pattern of small metabolic 'reactivation events' during a period of stress, which is most similar to what we see in warm-blooded hibernators today."

The study is published in Communications Biology.

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