Evidence of Hibernation-Like State Discovered in Tusks of Strange 250-Million-Year-Old Antarctic Creature

Researchers discover fossil evidence of a “hibernation-like” condition in the tusks of a 250-million-year-old Antarctic animal.

Among the many winter survival strategies in wildlife, hibernation is one of the most common. With limited food and energy sources in winter – especially in areas near or within polar regions – many animals hibernate to survive the cold, dark winters. Although much is known to behave in animals during hibernation, it is difficult to study fossils.

According to recent research, this type of adaptation has a long history. In an article published in the magazine on August 27, 2020 Communication biology, Scientists at Harvard University and the University of Washington report evidence of a hibernation-like state in an animal that lived in Antarctica in the morning Triadabout 250 million years ago.

The creature, a member of the genus Lystrosauruswas a distant relative of mammals. Lystrosaurus were common during the Permian and Triassic periods and are characterized by their turtle-like beaks and ever-growing tusks. While LystrosaurusMost of Antarctica was within the Arctic Circle and experienced extended periods of no sunlight each winter.

“Animals living on or near the poles have always had to deal with the more extreme environments,” said lead author Megan Whitney, Harvard University postdoctoral fellow in the Department of Organismic and Evolutionary Biology, who conducted this study as a UW PhD student in biology . “These preliminary results show that entering hibernation is not a relatively new type of adaptation. It’s ancient. ”

The Lystrosaurus Fossils are the oldest evidence of a hibernation-like condition in a vertebrate and indicate that solidification – a general term for hibernation and similar conditions in which animals temporarily lower their metabolic rate to survive a difficult season – is already present in vertebrates Mammals and Mammals Occurred Dinosaurs evolved.

Lystrosaurus arose before Earth’s largest mass extinction at the end of the Permian Period – which wiped out 70% of the vertebrate species on land – and somehow survived. It lived in the Triassic for another 5 million years and spread over parts of what was then the only continent on earth, Pangea, including what is now Antarctica. “The fact that Lystrosaurus survived end-Permian mass extinction and had such a broad spectrum in the early Triassic that they became a very well-studied group of animals to understand survival and adaptation, ”said co-author Christian Sidor, UW professor of biology and Curator of Vertebrate Paleontology at the Burke Museum.

Today find paleontologists Lystrosaurus Fossils in India, China, Russia, parts of Africa, and Antarctica. The creatures grew 6 to 8 feet long, had no teeth, but had a pair of tusks in their upper jaws. The tusks made the study of Whitney and Sidor possible because they are like elephants Lystrosaurus The tusks grew continuously throughout their life. Taking cross-sections of the fossilized tusks revealed information about Lystrosaurus Metabolism, growth and stress or strain. Whitney and Sidor compared cross-sections of tusks from six Antarctica Lystrosaurus to four cross-sections Lystrosaurus from South Africa. During the Triassic, the collection points in Antarctica were around 72 degrees south latitude – well within the Arctic Circle. The collection points in South Africa were more than 550 miles north, well outside the Arctic Circle.

The tusks from the two regions showed similar growth patterns, with layers of dentin being deposited in concentric circles like tree rings. The Antarctic fossils, however, had an additional feature that was rare or absent in tusks further north: closely spaced, thick rings, which the researchers said likely indicate periods of lesser deposition due to prolonged stress. “The analogue that we can find for the ‘stress marks’ observed in Antarctica Lystrosaurus Tusks are traces of tension in teeth that are associated with hibernation in certain modern animals, ”said Whitney.

The researchers cannot definitely conclude from this Lystrosaurus experienced a true hibernation. The stress could have been caused by some other form of freeze during hibernation, such as a short-term decrease in metabolism. Lystrosaurus Antarctica likely needed some form of adaptation to hibernation to cope with life near the South Pole, Whitney said. Although the earth was much warmer during the Triassic than it is today – and parts of Antarctica may have been forested – plants and animals below the Arctic Circle would still experience extreme annual fluctuations in the amount of daylight, with the sun being absent for long periods of winter.

Many other ancient high-latitude vertebrates may also have used freezing, including hibernation, to cope with the stresses of winter, Whitney said. But many famous extinct animals, including the dinosaurs, that evolved and spread afterwards Lystrosaurus extinct, have no teeth that grow continuously.

“To recognize the specific signs of stress and tension from hibernation, you have to look at something that can petrify and grow continuously throughout the life of the animal,” said Sidor. “Lots of animals don’t have that, but luckily Lystrosaurus did. “If analysis of additional Antarctica and South Africa Lystrosaurus Fossils confirm this discovery; it could also settle another debate about these ancient, hearty animals. “Cold-blooded animals often turn off their metabolism completely during a difficult season, but many endothermic or ‘warm-blooded’ animals that hibernate often reactivate their metabolism during hibernation,” said Whitney. “What we observed in Antarctica Lystrosaurus Tusks match a pattern of small metabolic “reactivation events” during a period of stress that most closely resembles what we see today in warm-blooded hibernation. “If so, this distant mammalian cousin is a reminder that many features of contemporary life may exist hundreds of millions of years before humans evolved to watch them.

For more information on this discovery, see Evidence of a “hibernation-like” condition discovered in the Early Triassic.

Reference: “Indications of solidification in the tusks of Lystrosaurus from the early Antarctic Triassic” by Megan R. Whitney and Christian A. Sidor, August 27, 2020, Communication biology.
DOI: 10.1038 / s42003-020-01207-6

The research was funded by the National Science Foundation. License numbers: PLR-1341304, DEB-1701383.