The discovery comes from Smiley Draw, a fossil site in Wyoming located outside the better-known Bighorn Basin. Researchers from the University of Kansas and the University of North Carolina at Greensboro say fossils from this less-studied locality complicate a classic evolutionary scenario involving Tetonius, a genus of omomyid primates. Omomyids were extinct early primates positioned near the evolutionary split that ultimately produced modern lemurs on one branch and monkeys, apes and humans on the other.

The new species was identified primarily from fossilized jaws and teeth, the parts of small mammals most likely to survive millions of years of erosion, burial and geological transformation. T. varleyorum was approximately the size of a modern mouse lemur, making its remains extremely difficult to locate in the field. Fossil crews must often screen or closely inspect large quantities of sediment to recover tiny teeth and jaw fragments that can reveal differences in species, diet and evolutionary relationships.

Parker Rhinehart, a doctoral student at the University of Kansas Biodiversity Institute and Natural History Museum and the study’s lead author, said the fossils add an important geographic dimension to the evolutionary history of Tetonius. For decades, much of the genus’s evolutionary narrative has been built from specimens collected in the Bighorn Basin. Those fossils were used to propose a gradual transformation from one form of Tetonius into another, with each successive population appearing to replace the previous one.

That model is known as anagenesis, a pattern in which a single lineage changes through time without splitting into multiple descendant branches. A landmark 1987 study by paleontologists Thomas Bown and Kenneth Rose presented the Bighorn Basin fossils as a prominent example of this type of evolutionary transition. The sequence became influential because it appeared to document anatomical change in a relatively orderly progression, particularly in the shape and structure of fossil Tetonius jaws.

The Smiley Draw fossils challenge the idea that this history was a simple, unbranching sequence. According to the new analysis, T. varleyorum does not fit neatly into the presumed transition represented by the Bighorn Basin specimens. Instead, its presence suggests that different Tetonius populations may have occupied separate regions at the same time, or that the genus diversified through branching speciation events rather than evolving along one continuous line.

This distinction matters because fossil records are often geographically incomplete. A sequence that appears linear in one sedimentary basin may look very different when fossils from neighboring regions are included. The apparent absence of branching can reflect a limited sampling area rather than the true evolutionary pattern. By adding Smiley Draw to the record, the researchers are expanding the geographic and ecological context needed to interpret the anatomical changes seen in early primates.

The new species also offers insight into Eocene biogeography, the study of how organisms were distributed across ancient landscapes. During this period, warm climates supported diverse mammalian communities, but local environments could still differ substantially. Populations separated by distance, habitat or geological barriers may have followed distinct evolutionary paths. The Smiley Draw fossils indicate that early omomyids may have been more regionally diverse than studies centered on a single basin had suggested.

The species name honors the Varley family, who operate a truck stop near the campground used by fossil researchers during fieldwork. Robert Anemone of the University of North Carolina at Greensboro discovered the Smiley Draw site and has led field investigations there for several years. K. Christopher Beard, a senior curator at the University of Kansas Biodiversity Institute and a professor in the Department of Ecology and Evolutionary Biology, is advising Rhinehart’s doctoral research.

The researchers plan to continue collecting at Smiley Draw, where additional jaws, teeth and other fragmentary remains could clarify the relationships among Tetonius species. Each new specimen may help determine whether the genus experienced multiple regional radiations, overlapping species distributions or more complex patterns of migration and replacement. For now, Tetonius varleyorum serves as a warning against treating apparently smooth evolutionary sequences as complete histories. In the fossil record, the missing branches may simply be waiting to be found.

Web References:
https://www.sciencedirect.com/science/article/pii/S0047248426000618
https://doi.org/10.1016/j.jhevol.2026.103867

References:
Journal of Human Evolution, DOI: 10.1016/j.jhevol.2026.103867

Image Credits:
Robert Anemone

Keywords:
Tetonius varleyorum, omomyid primates, Eocene, fossil primates, paleontology, evolutionary biology, anagenesis, speciation, Wyoming fossils, Smiley Draw, University of Kansas

The focus of this transformative study centers on Purgatorius, a diminutive arboreal mammal long regarded as the most basal and earliest known relative of all primates, including humans. Prior to this investigation, Purgatorius fossils were predominantly discovered in northern North America — notably Montana and the province of Saskatchewan. These northern finds formed the basis for hypothesizing a restricted latitudinal range for these primitive mammals during the Paleocene, limiting the understanding of their broader ecological spread.

Chester and his colleagues report the southernmost confirmed fossils of Purgatorius, uncovered within Colorado’s Denver Basin, specifically at the Corral Bluffs study area. Utilizing meticulous screen-washing of ancient Paleocene sediment layers, the team recovered minuscule fossilized teeth that exhibit a unique mosaic of dental traits, potentially indicative of a novel species within the Purgatorius genus. This discovery presents significant evidence that archaic primates dispersed southward rapidly after the Cretaceous-Paleogene mass extinction event — a period marked by profound faunal turnover and ecological opportunity.

These minute dental fossils display morphological features distinct from previously described species of Purgatorius, such as differences in cusp patterning and enamel thickness. These traits suggest adaptive responses to diversified dietary niches, possibly underpinned by ecological pressures linked to post-extinction vegetative recovery. The presence of such distinctive dental anatomy in southern latitudes implies an early radiation of primate relatives that was more geographically extensive and complex than formerly appreciated.

One of the cornerstones of this study is its methodological approach. The application of screen-washing—a technique that involves sifting through sediment with fine mesh to recover tiny fossil fragments often overlooked in traditional digs—has been pivotal in unveiling these crucial microfossils. Stephen Chester emphasizes that the under-sampling of microvertebrate fossils, particularly in southern regions, has artificially constrained our understanding of primate evolution. This provides a clarion call for expanded paleontological field campaigns employing refined recovery techniques to capture these elusive records.

The biogeographic implications of this research are profound. The data support a model whereby ancestral primates originated in northern North America but subsequently expanded into southern habitats during the earliest Paleocene. This range expansion may have facilitated adaptive radiations as these mammals faced varied ecological landscapes shaped by the aftermath of the dinosaur extinction. It reshapes prevailing paradigms, suggesting that the early biogeographic narrative of our primate lineage includes a broader distribution and possibly greater ecological plasticity than previously documented.

Moreover, this work advances the understanding of the immediate aftermath of the Cretaceous-Paleogene extinction. The survival and diversification of mammals like Purgatorius illuminate pathways through which vertebrate faunas rebounded, filling vacated ecological niches. The evolutionary trajectories documented by these fossils highlight the resilience and adaptability of early mammals, underscoring the pivotal role of primates’ ancestors in post-extinction ecosystems.

The study was made possible through a collaborative partnership with the Denver Museum of Nature & Science, blending expertise in vertebrate paleontology, sedimentology, and mammalian morphology. Co-authors include Jordan Crowell, a CUNY Graduate Center alumnus, alongside Tyler Lyson and David Krause of the Denver Museum, whose collective efforts facilitated both fieldwork and laboratory analyses critical to this project’s success.

Funding for this project is largely derived from a substantial $3 million National Science Foundation (NSF) grant awarded in 2023. This grant supports a multifaceted research program designed to uncover and interpret early mammalian fossils from the critical window after the dinosaur extinction. Integral to this initiative are Brooklyn College undergraduate research assistants, who have contributed tirelessly to sediment screen washing and fossil identification under Chester’s supervision. Their efforts continue to illuminate Paleocene vertebrate diversity with unprecedented detail.

This discovery’s resonance extends beyond academic circles; it contributes to the broader scientific narrative about human evolutionary origins. By elucidating patterns of early primate relative evolution, diversification, and dispersal, it lays foundational knowledge for tracing the deeper evolutionary roots that ultimately culminated in modern primates. The implications reverberate through fields including paleoanthropology, evolutionary biology, and earth sciences.

As Stephen Chester articulates, the research highlights critical gaps in the fossil record—especially relating to small vertebrates—and suggests that many important evolutionary events have yet to be fully documented. The ongoing refinement of excavation and analysis techniques promises to challenge entrenched assumptions and reveal the nuanced evolutionary dynamics of the earliest primates with greater clarity.

Further details and an accessible summary of this research can be explored via coverage in National Geographic, which highlights the significance of these southernmost Purgatorius teeth in rewriting anthropoid evolutionary history. This broader dissemination serves to inform and inspire both the scientific community and the interested public, generating renewed excitement in the quest to understand our distant biological heritage.

This milestone research enriches the paleontological literature through its innovative field methodology, collaborative integration of diverse scientific expertise, and the challenging of previously accepted biogeographic constraints. It serves as a testament to the continuing potential for discovery in the fossil record and the evolving story of mammalian—and primate—origins in a rapidly changing post-extinction world.

Subject of Research:
Not applicable

Article Title:
Southernmost occurrence of Purgatorius sheds light on the biogeographic history and diversification of the earliest primate relatives

News Publication Date:
March 3, 2026

Web References:
Journal of Vertebrate Paleontology article DOI: 10.1080/02724634.2614024
National Geographic coverage: https://www.nationalgeographic.com/science/article/purgatorius-teeth-primate-colorado

References:
Chester, S., Crowell, J., Lyson, T., & Krause, D. (2026). Southernmost occurrence of Purgatorius sheds light on the biogeographic history and diversification of the earliest primate relatives. Journal of Vertebrate Paleontology. DOI: 10.1080/02724634.2614024

Image Credits:
Credit: David Rozenblyum

Keywords:
Paleontology, Anthropology, Paleoanthropology, Primates, Purgatorius, Biogeography, Cretaceous-Paleogene Extinction, Mammalian Evolution, Paleocene, Fossil Discoveries, Evolutionary Biology, Vertebrate Paleontology