The discovery suggests our most ancient primate ancestors spread across North America far faster after the dinosaur extinction than the fossil record had previously shown.
DENVER — Paleontologists have unearthed fossils of Purgatorius, the earliest known relative of all primates including humans, at a site in Colorado’s Denver Basin, the southernmost location where the animal has ever been found and roughly 500 miles south of its previously known range.
The fossils, described March 3, 2026 in the Journal of Vertebrate Paleontology, consist of several tiny teeth recovered from the Corral Bluffs study area near Colorado Springs. Each tooth is small enough to fit on the tip of a baby’s finger. The find was led by Dr. Stephen Chester, associate professor at Brooklyn College and the Graduate Center of the City University of New York, in collaboration with researchers at the Denver Museum of Nature and Science.
Purgatorius is a shrew-sized mammal that first appears in the fossil record immediately after the asteroid impact that ended the dinosaurs approximately 65.9 million years ago. Until now, every confirmed specimen had been found in Montana or southwestern Canada.
Purgatorius is an extinct genus of eutherian mammal from the early Paleocene epoch of western North America.
The Colorado discovery extends its known range significantly southward and raises new questions about how quickly these early primates diversified and spread after the mass extinction.
“The discovery helps fill the gap in understanding the geography and evolution of our earliest primate relatives,” Chester said in a statement released by the Journal of Vertebrate Paleontology. “The presence of these fossils in Colorado suggests that archaic primates originated in the north and then spread southward, diversifying soon after the mass extinction at the end of the Cretaceous Period.”
Why the gap existed and how it was filled
The absence of Purgatorius fossils south of Montana had puzzled researchers for decades. Fossil-bearing rock of the right age exists throughout North America, and a diversity of later archaic primates has been found in the southwestern United States, but those specimens date to roughly two million years after Purgatorius first appears. The geographic and temporal gap left the early biogeographic history of primates poorly understood.
One hypothesis held that the absence was ecological. Purgatorius lived in trees, and forests in more southern regions may have been devastated by the asteroid impact, leaving the animal with no habitat to expand into. But paleobotanical colleagues of the research team found evidence that plant recovery in North America after the extinction event was rapid, undermining that explanation.
“Our paleobotanical colleagues suggested the recovery of plants in North America was fast, leading us to believe that Purgatorius should also be in more southern regions and perhaps we simply hadn’t looked hard enough,” Chester said.
The team took that suggestion literally. Using a labor-intensive screen-washing technique, funded in part by a nearly three million dollar collaborative grant from the National Science Foundation, researchers and volunteers sifted through large volumes of sediment from the Corral Bluffs site. The process, which had previously yielded fish, crocodilian, and turtle fossils, eventually produced a small number of Purgatorius teeth.
What the teeth reveal
The recovered teeth have a unique combination of features compared to known Purgatorius species, raising the possibility that they represent a previously undescribed species. Dr. Jordan Crowell, a postdoctoral fellow at the Denver Museum of Nature and Science who contributed to the study, said the team is waiting for additional material before making that determination.
The teeth also carry a methodological lesson. Traditional fossil collection in the region has relied on surface techniques practiced for nearly 150 years, which tend to recover only large fossils visible to the naked eye. Small mammals like Purgatorius are easily missed by those methods. The Colorado find suggests the fossil record for small early mammals across the American West may be substantially incomplete due to how paleontologists have historically searched for them rather than because the animals were absent.
“Our results demonstrate that small fossils can easily be missed,” Chester said. “With more intensive searching, especially using screen-washing techniques, we will undoubtedly discover many more important specimens.”
Why Purgatorius matters
Purgatorius sits at the base of the evolutionary lineage that eventually led to monkeys, apes, and humans. It is classified as a plesiadapiform, a group of archaic mammals considered the earliest primate relatives, distinguished from true primates but sharing key ancestral features. Ankle bones from previously recovered specimens indicate the animal lived in trees, placing it at the origin of an arboreal lifestyle that would persist through primate evolution for tens of millions of years.
The Colorado specimen places this founding lineage in an active recovery ecosystem immediately after Earth’s most recent mass extinction, at a moment when mammalian diversity was expanding rapidly into ecological niches left vacant by the disappearance of the dinosaurs.
Co-author Dr. Tyler Lyson, who leads the broader Corral Bluffs research project at the Denver Museum of Nature and Science, said the team is “building some incredible datasets that provide insights on how life, including our earliest primitive primate ancestors, rebounded after the single worst day for life on Earth.”
Source: Chester, S.R., Crowell, J., Lyson, T.R., and Krause, D. “Southernmost occurrence of Purgatorius sheds light on the biogeographic history and diversification of the earliest primate relatives.” Journal of Vertebrate Paleontology (March 3, 2026). DOI: 10.1080/02724634.2026.2614024.
Funding: U.S. National Science Foundation, David B. Jones Foundation, Leakey Foundation, Lyda Hill Foundation, Professional Staff Congress, City University of New York.
Quotes in this article are drawn from a press release issued by Taylor and Francis Group on March 3, 2026.
Jane holds a BSc in Biology from the University of Regina and a Master of Science in Bioscience, Technology and Public Policy from the Univesity of Winnipeg. Her reporting interests include Life Sciences, Physical Sciences and the Cosmos.