A team of paleontologists has discovered that a 250-million-year-old species of animal called Lystrosaurus likely relied on hibernation to survive back when Antarctica was still part of the ancient supercontinent known as Pangaea. The extreme survival tactic may have been instrumental in allowing the distant mammal relative to survive a mass extinction that wiped out 70 percent of all land-dwelling vertebrate species.
Two hundred and fifty million years ago, during the Early Triassic period, Earth’s landmass was collected into a single enormous supercontinent known as Pangaea. At this point in Earth’s history, the region that would one day become modern-day Antarctica was considerably warmer and more habitable than it is today.
This allowed a species of tusked, turtle-beaked vertebrate called Lystrosaurus to make its home in the inhospitable land. However, even in this more hospitable climate, the ancient Antarctic Lystrosaurus still had to endure long, cold periods in the winter months that were completely devoid of sunlight.
According to the results of a new study, Lystrosaurus was able to hibernate to survive during these stressful periods, and this biological strategy may have played a major role in allowing the species to survive a mass extinction that wiped out the majority of land-based vertebrates.
In the new study, paleontologists examined and compared the tusks of six Lystrosaurus from ancient Antarctica with four tusks that belonged to a separate population of the animals that lived closer to the equator, in a region that forms present-day South Africa.
The tusks of Lystrosaurus grew throughout the animal’s life, and their structure and makeup reflected periods of growth and strain, and even metabolic stress brought on by environmental factors. Because of this, scientists can learn a lot about the long dead species’ habits and survival strategies by analyzing the tusks in a similar way to how a researcher might examine the rings of a tree trunk to find out about climate change.
"To see the specific signs of stress and strain brought on by hibernation, you need to look at something that can fossilize and was growing continuously during the animal's life," commented co-author of the new paper Christian Sidor, a professor of biology at the University of Washington and curator of vertebrate paleontology at the Burke Museum. "Many animals don't have that, but luckily Lystrosaurus did."
The team made cross sections of tusks from both populations, and examined the frequency and patterns of growth marks, and ring-shaped deposits of dense, bony tissue called dentin.
It was discovered that the spaces between growth marks in both populations were very similar, suggesting that the two groups had a closely shared physiology. However, the team found indicators of metabolic stress in the tusks of Lystrosaurus from Antarctica, which came in the form of closely spaced, thick layers of dentin, which were not exhibited by the population closer to the equator.
According to the authors of the study, these unusual dentin deposits suggests that the Antarctic Lystrosaurus went though seasonal hibernation-like periods of torpor, during which they reduced their metabolic activity.
"The closest analog we can find to the 'stress marks' that we observed in Antarctic Lystrosaurus tusks are stress marks in teeth associated with hibernation in certain modern animals," said lead author Megan Whitney, a postdoctoral researcher at Harvard University in the Department of Organismic and Evolutionary Biology.
Whilst the team was unable to unequivocally prove that the Lystrosaurus underwent hibernation, it would help explain how they were able to survive the environmental stresses that brought about the end-Permian mass extinction. If proven correct, the fossils would represent the oldest evidence of hibernation in a vertebrate animal discovered to date
The paper has been published in the journal Communications Biology.
Source: University of Washington
