Recent discoveries of minuscule fossils belonging to Purgatorius, the earliest known ancestor of all primates, including humans, have emerged from a new location in southern North America. This finding is poised to enhance our understanding of the evolution and dispersal of primates across the continent.
The origins and early geographic distribution of primates have been subjects of extensive research and debate. Purgatorius, a small mammal comparable in size to a shrew, first appeared in the fossil record shortly after the extinction of the dinosaurs, approximately 65.9 million years ago, and is recognized as the oldest archaic primate.
While rock formations from this era are prevalent throughout North America, fossils of this species had previously been confined to Montana and parts of southwestern Canada. Other early primate relatives discovered in the southwestern U.S. date back about two million years later, creating a notable gap in the fossil history until now.
According to research published in the Journal of Vertebrate Paleontology, these newly identified fossils represent the southernmost record of Purgatorius, found in the Denver Basin of Colorado at the Corral Bluffs study site.
Insights into Early Primate Distribution
Lead author Dr. Stephen Chester, an associate professor at Brooklyn College and The Graduate Center, CUNY, emphasizes that this discovery fills a significant gap in understanding the geographic and evolutionary pathways of our earliest primate relatives. He notes that the presence of these fossils in Colorado indicates that archaic primates likely originated in the north and subsequently migrated southward, diversifying shortly after the mass extinction at the close of the Cretaceous Period.
Fossilized ankle bones suggest that Purgatorius was arboreal, leading researchers to initially believe that its absence south of Montana was due to widespread forest destruction from the asteroid impact 66 million years ago. However, insights from paleobotanists indicate that plant recovery in North America occurred rapidly, suggesting that Purgatorius could have inhabited more southern regions if they had searched more thoroughly.
Innovative Fossil Recovery Techniques
To enhance their search, Dr. Chester and his team employed an intensive screen washing technique to sift through sediment for tiny fossils. This initiative was partially funded by a nearly $3 million grant from the National Science Foundation, which supports broader research on life recovery post-mass extinction.
Students and volunteers meticulously washed and sorted large quantities of sediment, uncovering various fossils, including several tiny Purgatorius teeth, each no larger than the tip of a baby's finger. Dr. Jordan Crowell, a postdoctoral fellow at DMNS, expressed excitement over the potential that these teeth may belong to an even earlier species of Purgatorius.
Revisiting Fossil Sampling Methods
This discovery also highlights the possibility that the perceived absence of early primate relatives in southern regions was influenced by sampling bias. For nearly 150 years, paleontologists have predominantly relied on surface collection methods, which tend to overlook smaller fossils.
Dr. Chester concludes that with more rigorous searching techniques, particularly screen washing, many more significant specimens are likely to be uncovered, further enriching our understanding of primate evolution.