Tiny teeth found in Colorado deepen the debate over primate origins
A sediment-washing “bubbler” helped researchers recover 65.5-million-year-old teeth that illuminate how early primate relatives spread after the mass extinction.
Last year, National Geographic Explorer Tyler Lyson was in Corral Bluffs on the outskirts of Colorado Springs, searching for minuscule fossils. His tool of choice? A unique filtering machine called a “bubbler.”
The device pipes compressed air into a large tub of water, where a steady stream of bubbles helps break apart sediment and trap bone fragments on sieve-like screens. After sifting through several tons of earth, his team retrieved a diminutive tooth. It was one of three they identified as belonging to a Purgatorius, a small tree shrew-like animal thought by many scientists to be the world’s earliest primate.
“To find these three teeny tiny teeth we had to screen-wash over 8,000 pounds of dirt,” says Lyson, a paleontologist at the Denver Museum of Nature and Science. “It took an army.”
Lyson and his team dated the teeth to 65.5–65.4 million years ago, or about 550,000 to 650,000 years after the asteroid-driven cataclysm that wiped out the nonavian dinosaurs. The three teeth are also the farthest south that Purgatorius remains have been found so far.
The findings, published Tuesday in the Journal of Vertebrate Paleontology, offer tantalizing clues into how primitive primates initially evolved and proliferated in a dinosaur-free world.
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Prior research based on several teeth and a rare ankle bone reported in 2012 indicates Purgatorius ate fruit, climbed trees, and had eyes on the sides of its head like a squirrel. While these findings provide insight into how Purgatorius lived, scientists’ understanding of its habitat and migration remains limited. Because Purgatorius is so small, scientists have had difficulty finding its remains, particularly with conventional excavation techniques, such as digging with a chisel and trowel.
“It could fit in the palm of your hand.” says Stephen Chester, a paleontologist at Brooklyn College in New York who discovered the Purgatorius ankle bone and is lead author of the new study. “A Purgatorius tooth is around two by two millimeters, so the chances of finding that with your naked eye are extremely small.”
Primitive primates
Purgatorius sits at the heart of a debate about the world’s first primates. The earliest definitive primates appear in two groups: adapiforms (lemur-like primates) and omomyiforms (close relatives of tarsiers). They both date back to about 56 million years ago, but the relationship between these two types of primates and those that came shortly after the dinosaur-killing impact—some 10 million years earlier—is unclear.
Purgatorius belongs to a group called plesiadapiforms, which many scientists consider to be the primates that precede these other two groups, but some argue they are not true primates. The oldest Purgatorius remains come from Montana, and suggest the tiny animals scurried onto the scene around 65.9 million years ago, or 100,000 years after the end-Cretaceous extinction event.
Around 1.9 million years later, relatives of Purgatorius began to appear farther south in places like New Mexico. While these discoveries provide a few more pieces of the Purgatorius puzzle, they leave many questions unanswered about how and where they originated and subsequently migrated during that 1.8-million-year gap.
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The three newly discovered teeth from Colorado expand Purgatorius’s known range from Montana and southwestern Canada southward into the more western central United States.
Dorien de Vries, a paleontologist at the Naturalis Biodiversity Center in the Netherlands who was not involved with the research, says the paper “illustrates the remarkable evolutionary success and adaptability of these early primates.”
She added that the discovery shows that Purgatorius’s habitat after the asteroid impact was much greater than previously thought. “It teaches us more about the origin of primates themselves, and what the earliest members of our family looked and lived like,” she says.
Gregory Wilson Mantilla, a paleontologist at the University of Washington who was not involved with the new findings, says the new teeth show “there is much more to be discovered even in the well-explored western interior of North America.”
He, along with Chester, discovered the oldest-known Purgatorius fossils in Montana in 2021. “Despite decades of paleontological field work, we are just scratching the surface,” Wilson Mantilla says.
Though the three teeth belong to a presently unidentified and likely new species of Purgatorius, the researchers want to unearth more remains before they definitively make that claim.
“We're going to find a head at some point,” says Lyson. “The best fossils are still in the ground.
