By Andrew Rossi. Originally published in Cowboy State Daily on December 1, 2024.
Scientists from the Duke Lemur Center at Duke University come out to Wyoming every summer to find fossils from the earliest ancestors of modern-day lemurs and primates. They say the Bridger Basin is the Madagascar of the Eocene Period.
There are plenty of lemur-like mammals in Wyoming. That’s why the Duke Lemur Center at Duke University comes out every summer to find them and reveal their secrets.
The Duke Lemur Center has the most diverse population of living lemurs outside of Madagascar, their only remaining habitat on the planet. Its mission is to converse lemurs in the wild since 90% of these unique primates could be extinct before the end of the century.
For scientists like Matthew Borths, a paleontologist curator of fossils at the Duke Lemur Center Museum of Natural History, the key to preserving the future of lemurs in the present is a better understanding of their prehistoric past. But he doesn’t go to Madagascar to tell that story.
Borths has been leading scientific expeditions into Wyoming’s Bridger Basin to find fossils from the earliest ancestors of modern-day lemurs and primates. Someday, he may even find fossils of the tiny primate-like creature that laid the foundation for humanity.
“Our mission is to follow the primate story around the world,” Borths told Cowboy State Daily. “The primate story starts in North America, and some of the best specimens from the story have come from Wyoming.”
Eocene Origins
It was 56 million years ago. Dinosaurs had been dead and buried for more than 10 million years, the climate was the warmest it had been in eons and mammals were capitalizing on it by growing, diversifying and taking over the planet.
“This is the moment when evolution asks, ‘Who will inherit the world from the dinosaurs?’ and it’s the mammals that answer the question,” Borths said. “This is when mammals start to diversify and get big.”
This is the Eocene Period, roughly from 56 million to 34 million years ago. Some of the best rock exposures from this critical moment in mammalian history are stretched across Wyoming.
Wyoming’s Eocene exposures have been the subject of intense scientific scrutiny for a century. Along with what has been uncovered in the
Bridger Basin, excavations in the Bighorn Basin revealed the best specimens of Plesiadapis, the earliest known primate-like mammal in the fossil record.
The Duke Lemur Center has a remarkably well-preserved fossil of Notharctus, a lemur-like mammal with adaptations like grasping hands and forward-facing eyes that would become standard for lemurs and primates. Borths said this Wyoming specimen, the largest mammal ever up to that time, changed the paleontological perspective on the origins of early primates.
“The old picture of what Eocene primates look like is a little bit wrong,” he said. “This specimen is a better model for what the ancient animals looked like, and we can plug that into models of living lemurs to figure out how their lemur-like ancestors moved and where our human bodies came from.”
Modern Madagascar in Prehistoric Wyoming
Borths’ prehistoric primate research is focused on the badlands of the Bridger Basin, a colorful region of rock layers in southwest Wyoming. It’s been one of Wyoming’s many paleontological hotspots for more than a century.
“It’s the next day, geological speaking,” Borths said. “Dinosaurs go extinct 66 million years ago, and this stuff is around 56 million years old. This is where we start to find primates in the fossil record in North America.”
Fossils from the Bridger Basin are in museums worldwide, from the tiny skeletons of the earliest horses to the giant Uintatherium, an extinct hoofed herbivore with horns and saber teeth. The world would have looked and felt like modern-day Madagascar, so Borths expects to find the lemur-like mammals that lived there.
“The Bridger Basin is the Madagascar of the Eocene,” he said. “We transition from a few primates on the landscape to a lot of diversity, hopping around in the rainforests of Wyoming.”
However, the increased diversity of primitive primates decreased soon after its peak, with several species going extinct before the end of the Eocene. The Bridger Basin could complete the missing part of the “sandwich” of primate evolution that Borths is trying to piece together with more fossils, which also come in pieces.
“As you go into the Eocene, you start to lose primate diversity in North America,” he said. “How did we get this primate diversity, and then how do we lose that diversity? There’s always more to be found.”
Substantive Scraps
Borths and his teams have spent several summers combing the Bridger Basin for Eocene fossils. They haven’t found much, but every piece is potentially promising.
“These aren’t places where you find skeletons,” he said. “Instead, we find things like isolated teeth. So, we have to extract as much information as possible from some really unspectacular materials.”
The new sites are part of the “sandwich search” to explain the rise and fall of primate diversity in the Eocene. Once again, the badlands of Wyoming could be the critical proving ground for an important paleontological breakthrough.
Fossil preparators at the museum’s laboratory are now working on several blocks containing pieces and parts collected from these sites. While they etch away the rock encasing the fossils, each specimen is CT scanned to reveal more fossils and other scientific information hidden in the rock.
“Field work always moves ahead of published work,” Borths said. “All the specimens that have come out of the Bridger Basin recently are being scanned as part of a big research project presenting all of this information, but we’re mostly working with pieces right now.”
Yesterday’s Tomorrow
While the details of the ongoing research are still being compiled, Borths believes they’ve found clues supporting a broader theory of what happened in the Bridger Basin at the end of the Eocene. The diversity of Wyoming’s lemur-like mammals disappeared along with their tropical habitat.
“There’s a huge cooling event when the Eocene ends and the Oligocene begins,” he said. “Suddenly, there’s ice in Antarctica and the North Pole. That changes ocean currents, which changes everything, and primates go extinct at that point.”
This fossil research contributes to the mission of the Duke Lemur Center. Many of Madagascar’s lemurs are endangered due to environmental and human-caused factors, including climate change.
Borths already sees parallels in the extinction of the lemur-like primates in prehistoric Wyoming and the existential threats to their modern-day descendants. Understanding their decline in the Eocene might help preserve modern-day biodiversity.
“Primates are going extinct in Madagascar right now, soon can making connections between the Bridger Basin 57 million years ago and Madagascar today,” he said. “What part of primate diversity do we lose first? What are the last survivors, and what do they look like? And then when do they finally wink out? That’s the next phase of this research.”
Humanity’s Holy Grail
The Duke Lemur Center has already made several significant discoveries from the fossils of lemur-like primates in Wyoming. They’ll be studying those fossils for years and will return to the Bridger Basin to collect more fossils for their research.
Borths isn’t expecting to find a “Holy Grail” specimen during his excavations, but he does have something at the top of the wish list. The ultimate discovery would be the tiny fossils of humanity’s earliest known ancestor — something that could be found in the Bridger Basin.
“We have great pieces to tell the story of these lemur-like mammals,” he said. “The dream would be to find pieces of the monkey-like mammal story from that same time. I’d love to find an omomyid in the Bridger Basin.”
Omomyids are an extinct group of tiny primates that lived during the Eocene. They were considerably smaller than the lemur-like primates Borths and his team have found up to this point, which makes them extremely rare in the fossil record.
“Big animals are more likely to be preserved than smaller animals,” he said. “There are tons of mice in the world, but the world isn’t covered in mice skeletons because those get broken down by wind and rain much more quickly than cow bones.”
The potential of finding an omomyid is so exciting because these tiny primates are more directly related to humans. They are humanity’s closest ancestor from that period in the fossil record.
“It’s a little frustrating that we haven’t found any of these yet, but that remains the quest,” Borths said. “It’s why we go back to some sites that have been known for a century; there’s always the possibility we’ll find that skeleton that’s been exposed. Every Wyoming thunderstorm is a new opportunity because there’s more material to be found.”
Hopping Around The World
The Wyoming fossils collected by Borths and his colleagues are on display at the Duke Lemur Center’s Museum of Natural History in Durham, North Carolina. Since they were found and collected on federal land, the specimens are available to anyone who wants to see and research them.
There are also plenty of living lemurs to visit at the Duke Lemur Center as biologists study their anatomy and behaviors, trying to understand their ways and prevent their extinction. The past, present, and future connections make Borths’ paleontological research in Wyoming so rewarding.
“The primate story starts in North America, and some of the best specimens come from Wyoming,” he said. “From there, the story shifts into Africa, so then we go to Egypt to collect material from Egypt, and then we get to Madagascar to pick up the pieces preserved there. It’s about picking up the pieces from the prehistoric so we can understand how to protect these animals in the future.”
