How can I tell if something that died 250 million years ago when he was alive?
After all, hibernation – a state of reduced metabolism – is a good strategy to make it through long, harsh winters when food can be scarce. Biologists would not be surprised if evolution invented this early in the history of life. But convincing convincing evidence of that is difficult.
“As a paleontologist, what you are offered is a pile of bones,” said Christian A. Sidor, a professor of biology at the University of Washington and curator of vertebrate paleontology at the Burke Museum in Seattle. “And that just tells you where the animal died. It does not even tell you where the animal lived. ”
Mar Dr. Sidor and Megan R. Whitney, a former student who is now a postdoctoral researcher at Harvard, believe they have good evidence of winter slaughter behavior in an animal that lived in Antarctica a quarter of a billion years ago – before the age of dinosaurs.
This was a tumultuous time for life around the planet, recovering from the largest mass extinction ever on Earth, marking the end of the Permian geological period and the beginning of the Triassic. Antarctica, then as now, was close to the South Pole, and would probably have provided some port of disaster, often called the Great Dying. (The cause of this extinction is still debated.)
Dr. Whitney said that this animal, Lystrosaurus, was about the size of a middle dog with a beak like a tortoise and two small branches, and it was one of the species to make it through mass extinction.
“It’s a strange animal,” she said. ‘It’s a kind of sausage shape. And it had no teeth except the two teeth that came out of its face. “
Despite its dinosaur-sounding name – it means in Greek “scopagdis” – this creature was more closely related to mammals.
The teeth – only a few centimeters long, probably used to dig up roots and tubers for food – gave the signs of signs that the metabolism of Lystrosaurus periodically slowed down.
As with modern elephants, the Lystrosaurus teeth grew continuously. Thus, a thin cross section of a branch produced a record of the animal’s life, just like tree rings, with alternating dark and light circles. Dr. Whitney and Dr. Sidor compared the patterns in the teeth of six Lystrosaurus living in Antarctica with four from South Africa.
The Antarctic teeth enclosed dense rings at great distances – probably periods where the growth of the teeth slowed down, perhaps stopped due to stress – while the South African did not.
Although all the land of the earth at that time was combined in the supercontinent Pangea, the part that is now Antarctica was still close to the South Pole and the part that is now South Africa was still hundreds of miles to the north.
Temperatures were then warmer, so Antarctica was not covered with ice sheets. But the earth was tilted about the same as it is now, which would have led to winter days leading to short days. The dark days would slow down the growth of plants, leaving food for herbivores such as Lystrosaurus to eat.
Thus, the researchers interpreted the thick, dark rings as a result of hibernation-like metabolism. The patterns are similar to what is seen in the teeth of modern mammals that hibernate in winter.
The findings also suggest that Lystrosaurus was warm-blooded. While the metabolism of cold-blooded reptiles can often shut down completely, mammals wake up periodically on their own.
The findings were published Thursday in the journal Communications Biology.
“The idea that they say, OK, there’s actually some interesting variation in the size of these features that tells us about the life history of animals,” said Kenneth Angielczyk, curator of paleomammology at the Field Museum of Natural History in Chicago. , “That’s something new and quite interesting.”
Dr. Angielczyk was not involved in the Lystrosaurus study, although he collaborated on other projects with Dr. Pages and Dr. Whitney.
Whether Lystrosaurus actually hibernates or otherwise slows down its metabolism – biologists refer to the strategies as torpor – may never be known.
“This is a first study of its kind,” said Drs. Whitney, “that it will be preliminary.”
