Mammal ancestors survived a mass extinction – but got killed off by drought.

Live Science considers the fate of the shovel lizard Lystrosaurus, a plant-eating creature from 251 million years ago who survived the Permian-Triassic mass extinction, but then was wiped out by a massively changing climate:

The researchers first found the fossils 11 years ago in the desert Karoo region of South Africa. During an excavation, they unearthed 170 tetrapods, or four-footed animals in about 6.5 feet (2 meters) of sandstone, including multiple clusters of these lystrosaurs. These odd creatures were like no animal alive on Earth today. They were part of a group called therapsids, an extinct order of reptiles that includes mammal ancestors (mammals are the only therapsid descendents that still persist today). They were shaped a bit like a “bulldog with a beak and some tusks,” [Field Museum of Natural History in Chicago fellow Pia] Viglietti told Live Science.

The fossils suggest that the young lystrosaurs may have clustered together before they died, probably on a floodplain where they had hope of finding water and vegetation. This sort of behavior is still seen today during droughts in sub-Saharan Africa, Viglietti said, where animals gather around dwindling sources of water and food before succumbing to thirst and starvation.

Two of the fossils found in the Karoo sandstones left skin impressions in the surrounding rock, indicating that the animals may have dried out and mummified rapidly after death, before being buried and fossilized. These two “mummies” were fossilized next to each other, their limbs sprawled out.

“They were both spread-eagled, almost like they had died while going somewhere,” Viglietti said. “Literally stopped in their tracks.”

Lystrosaurs didn’t go extinct for another few million years. The fact that they lived at all when so many other species perished is sometimes held up as evidence that the planet recovered fairly quickly from the climate mess at the end of the Permian, which was caused by huge Siberian volcanoes belching gasses into the atmosphere. But the discovery of a population struggling under the stress of repeated droughts suggests that Earth didn’t recover quickly at all, Viglietti said.