Evidence: Species that roamed with dinosaur survived mass extinction due to 'hibernation'

A new study found that the Lystrosaurus species that roamed with dinosaurs went into state of hibernation and survived Earth’s largest mass extinction that wiped out 70 per cent of species on Earth. According to a study published in the journal Nature, scientists at the University of Washington found that Lystrosaurus somehow survived for another 5 million years into subsequent Triassic Period on the continent, Pangea, present day Antarctica. The four-legged foragers helped scientists understand the phenomenon and history of hibernation of species in polar regions that get through tough conditions like food scarcity, temperatures fall, and dark environment and still survive. 

Scientists at University of Washington and its Burke Museum of Natural History and Culture found the evidence that hibernation-like state in an animal is key to survival in most unfavourable conditions, as it had helped species in Antarctica during the Early Triassic, some 250 million years ago. In the study, scientists mentioned the research findings that said, adaptation to ‘hibernation-like’ state without sunlight in tough winters has a long primitive history.

Lystrosaurus’ in the present day Antarctic Circle, millions of years ago went into state of torpor — term for hibernation. This lowered their metabolic rate  that eventually helped them survive tough conditions. A postdoctoral researcher at Harvard University who also conducted this study as a UW doctoral student in biology, author Megan Whitney said, "Animals in the polar regions have always had to cope with the more extreme environments.” She added, “These preliminary findings indicate that entering into a hibernation-like state is not a relatively new type of adaptation. It is an ancient one.”

“Cold-blooded animals often shut down their metabolism entirely during a tough season, compared to many endothermic or ‘warm-blooded’ animals,” Whitney said in the study. Lystrosaurus tusks indicated metabolic ‘reactivation events’ like warm-blooded hibernators today, she added, which indicates species is a distant cousin of Antarctic hibernating mammals. 

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[Ancient vertebrate Lystrosaurus at high latitudes used torpor, including hibernation. Credit: Twitter/@PrimordialProse]

[Oldest instance of torpor yet reported in the fossil record of Lystrosaurus. Credit: Twitter/@paleowire]

Key to understand 'survival and adaptation'

Lystrosaurus had survived the end-Permian mass extinction and entered the early Triassic. The species is the key to understanding the survival and adaptation in group of animals in Antarctica today, co-author Christian Sidor, a UW professor of biology and curator of vertebrate paleontology at the Burke Museum said in the study. According to the research, the fossils of Lystrosaurus have been found in India, China, Russia, parts of Africa and Antarctica. Mostly pig-sized, some 6 to 8 feet long with a pair of tusks these species survived on ground vegetation and dig for roots and tubers.

Scientists compared cross-sections of tusks from six Antarctic Lystrosaurus to cross-sections of four Lystrosaurus from South Africa in the research. The site in Antarctica where fossil was collected was 66.3 degrees south. In South Africa 550 miles north, fossils from Triassic period were found. Comparing the tusks, scientists found closely-spaced, thick rings, which indicated periods of less deposition due to the form of torpor. The tusks indicated the long reduction in metabolism, body temperature and activity in Lystrosaurus suggesting hibernation-like adaptation that helped species survive mass extinction. 

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