A sudden climate shift 252 million years ago wiped out a huge amount of animal species. But one species that not only survived but thrived had an amazing way of staying alive: they lived fast, and they died young.

That appears to be the key to survival, based on a new study from researchers who examined growth patterns in ancient mammals called therapsids that resided in the South African Karoo Basin, according to a University of the Witwatersrand statement.

The climate shift was caused by Siberian volcanoes that blasted carbon into the atmosphere and totally shifted the Earth’s climate, wiping out most animals who couldn’t handle the sudden change. But therapsids thrived in these new conditions, which intrigued paleontologists who wanted to know why.

Lystrosaurus, one of the species they examined, had a life span of 13 or 14 years before the extinction event. But after the event, scientists say that the record of growth preserved in their bones showed that they lived just two to three years old, so they must have bred relatively young.

And it shrunk, too. Lystrosaurus would have been the size of a pygmy hippo before the extinction, but afterward it was the size of a large dog.

This creature went on to dominate the landscape, making up 70 to 90 percent of vertebrate fossils scientists have found in Karoo from the Early Triassic period.

“Before the Permo-Triassic extinction, the therapsid Lystrosaurus had a life span of about 15 years based on the record of growth preserved in their bones,” National Museum palaeontologist Jennifer Botha-Brink, the lead author on the paper, said in the 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 juveniles themselves.”