The Mass Extinction Detectives: Sterling Nesbitt contributes to NPR’s Science Friday


Randy Irmis is kneeling next to a prehistoric burial site in the walls of a canyon in the Utah desert. Just inches under his fingertips is the skull of a 210-million-year-old creature entombed in the gritty sandstone. But as Irmis huddles on the narrow ledge and chips away at the block with a chisel and hammer, he notices—to his alarm—he has unearthed a crack.


“You see the crack there?” Irmis asks Andrew Milner, one of the two other team members on the dig and a paleontologist from the St. George Dinosaur Discovery Site at Johnson Farm.

Milner observes the gash beginning to splice farther down the length of the slab and a nascent network of fissures. “I bet you anything if we pull [one piece of the rock] off, it would split perfectly on the side of the head,” Milner says. Then, reconsidering, he adds with a laugh, “But then again, maybe not.”

“Yeah, I don’t want to chance that,” Irmis agrees.


For fossil hunters Irmis, Milner, and volunteer Cody Rock, it’s been a full day at Bears Ears National Monument—hiking up steep terrain, removing and sawing rock in arid 90-degree Fahrenheit heat, and shimmying precariously along a skinny ledge overlooking Indian Creek. The last thing they want is to damage their prize, especially one so rare to come by: A skull of one of the top predators of the late Triassic, the phytosaur.

“We’re lucky if we find one skull a season,” says Irmis, curator of paleontology at the Natural History Museum of Utah and associate professor at the University of Utah. “If you think about a skeleton of any animal, there’s only one skull, but there’s many ribs, there’s many vertebrae, there’s two of each type of limb. So you don’t find a lot of skulls. So that’s always really exciting.”

Just by looking at the block still embedded in the ridge, Milner can already imagine the skull, with its signature slim snout. “From what I can see, that’s just a beautiful fossil laying there. I really can. It’s going to be spectacular when it’s prepared.”

When it was alive, this large, crocodile-like reptile lurked in the swamps and rivers of the Triassic—a time period spanning from about 252 to 201 million years ago. These armor-plated beasts could grow up to 30 feet long and used their toothy snouts to snap up prey in land and water. They even feasted on early dinosaurs for dinner.

While these phytosaurs swishing in Triassic waterways may look similar to modern-day crocodilians, the mighty beasts are not related to crocodiles or alligators. Illustration by Franz Anthony

But then, after thriving for 35 million years, the mighty phytosaurs fell victim to extinction. “It’s always sort of a mystery when you see this group that is super, super successful,” Irmis says. “These are some of the most common fossils we find in the late Triassic, and then they die out pretty suddenly and it’s hard to say exactly why that happened.”

What happened next is a blur in Earth’s history that Irmis and a band of extinction detectives are trying to piece together. It’s a crucial period when the dinosaurs transformed from the underdogs phytosaurs ate for dinner to the thundering, planet-ruling creatures we remember them as today.

It’s known as the End Triassic mass extinction. It’s one of the five most devastating mass extinctions in Earth’s history, a group collectively referred to by researchers as “the Big Five.” While an estimated 80 percent of species were lost, this extinction has “no smoking gun,” says Sterling Nesbitt, a paleontologist at Virginia Tech. “There is nothing we can really put our finger on and say, ‘This is what killed all of these animals,’ compared to what we see in the Permian and in the Cretaceous.”

If you were to trace your finger along the geologic timeline, Nesbitt says, “it’s like you have happy Triassic fauna with a few dinosaurs in there, then big question mark, and then lots of dinosaurs without all the classic Triassic reptiles,” Nesbitt says. This mystery is what drives Irmis, Milner, and a team of paleontologists and volunteers to Indian Creek in Bears Ears National Monument, the hotly contested nature preserve 105 miles south of Moab in southeastern Utah, where they scavenge all the clues they can from a key rock formation.


Investigating this prehistoric crime scene doesn’t just help paleontologists understand past creatures. It’s a case that helps scientists better understand the climate change and species loss we are experiencing today—and might even clue them into our planet’s potentially foreboding future.

Methods, from Science Friday: Why Is This A Story Worth Telling?

Often we look to models and projections to understand the future of our planet, but so much can be learned from the past. The End Triassic mass extinction, during which the dinosaurs came out on top, holds many similarities to today’s climate change yet very little is known about it. The fossils of the Triassic provide crucial information for filling in Earth’s early timeline, and the paleontologists studying this period’s climate could help us understand our changing climate today.