To Save Their Species, These Prehistoric Animals Mated Early and Died Young

For better or worse, every organism is affected by the world around it. Changes in climate or available resources can inspire animal species to relocate, grow bigger or smaller, quit migrating, and even fall down more. Now a group of scientists say a mass extinction event inspired a prehistoric mammal ancestor to condense its lifespan. Their paper was published today in the journal Scientific Reports.

The Lystrosaurus was a charmingly dumpy creature: As you can see in the depiction above it's a bit like a cross between a corgi, a naked mole rat, and an iguana. Therapsids like Lystrosaurus and their cousins the cynodonts roamed the planet 250 million years ago—which was, unfortunately, not a great time to be alive. A series of volcanic eruptions filled the atmosphere with carbon, thereby seriously disrupting the planet’s climate and leading to a mass extinction event. Up to 96 percent of aquatic species were lost, as were around 70 percent of land species. Somehow, through all this, sturdy Lystrosaurus managed to hang on.

Scientists have developed a number of theories on the therapsids' success, including their fondness for underground living, their willingness to travel, and sheer dumb luck. The latest report proposes a new strategy: living fast and dying young.

A team of paleontologists from the U.S. and South Africa examined the tissue microstructure of bones from 103 therapsid specimens. (Bones, like tree rings, are a great way of studying how an individual has aged, and how much.) The specimens represented around 20 million years of evolution, including the periods before, during, and after the mass extinction event.

Image Credit: The Field Museum

The researchers found that, while the therapsids had survived, they’d undergone some major changes. After the event, Lystrosaurus and some of its cousins were quicker to reach maturity, and their lives were much shorter.

“Before the Permo-Triassic extinction, the therapsid Lystrosaurus had a life span of about 13 or 14 years based on the record of growth preserved in their bones,” co-author Ken Angielczyk, of The Field Museum, said in a press statement. “Yet, nearly all of the Lystrosaurus specimens we find from after the extinction are only 2–3 years old. This implies that they must have been breeding when they were still juveniles themselves.”

Post-extinction therapsids had also shrunk. Before the volcanoes, Lystrosaurus was about the size of a little hippopotamus. After, a full-grown animal was closer in size to a large dog—partly because it was so much younger than its ancestors.

How could this have helped? The research team ran computer simulations to model the therapsids’ environment. The simulations revealed that maturing fast and mating young could have increased therapsid species’ chances of survival by as much as 40 percent. The individuals died, but their family lived on.

“With the world currently facing its sixth mass extinction, paleontological research helps us understand the world around us today,” Angielczyk said. “By studying how animals like Lystrosaurus adapted in the face of disaster, we can better predict how looming environmental changes may affect modern species.”