The rodent-like climber that paved the way for primates

Nature · Published 19 October 2026 Swipe more like this →

In short: For decades, our understanding of the earliest primates was limited to a few teeth and jaw fragments. New research into the ankle bones of a mouse-sized creature called Purgatorius has finally revealed how these ancestors moved, showing they were nimble tree climbers that co-evolved with the world's first fruits.

Purgatorius was a small, rat-sized mammal that lived during the early Paleocene epoch, roughly 65 million years ago, shortly after the mass extinction of the dinosaurs. While it was long considered a potential primate ancestor, scientists previously lacked the skeletal evidence to confirm its lifestyle. It was only through the identification of specific ankle bones from Montana that paleontologists could confirm the species possessed a wide range of motion in its joints, indicating it was a proficient tree climber rather than a ground-dwelling mammal.

This discovery provides critical evidence for the co-evolutionary relationship between early primates and flowering plants. As plants began to produce fruit to attract seed dispersers, primates were becoming specialized for life in the canopy. By developing the ability to climb out onto branches to collect fruit, Purgatorius gained a significant competitive edge over land-dwelling mammals. This ecological niche likely contributed to the evolutionary success of the primate lineage, allowing them to exploit new food resources as the terrestrial landscape shifted.

The ability to identify these fossils has been bolstered by the work of paleontologists like Jonathan Bloch, who used formic acid to dissolve limestone and reveal nearly complete skeletons of other early primates. These specimens serve as a 'Rosetta stone,' allowing researchers to positively identify isolated bones like those of Purgatorius in existing collections. Moving forward, researchers aim to use these findings to better understand the animal's posture and the broader origins of primates in the wake of the K-Pg boundary.

While Purgatorius is often cited as the earliest primate or protoprimate, its exact taxonomic placement remains a subject of study. Some records, such as P. ceratops, were initially thought to be from the Late Cretaceous due to their proximity to dinosaur fossils, but later analysis suggests they actually date to the early Paleocene. The genus is currently known from at least five species across western North America, ranging from Montana to Colorado.

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