The forests that gave rise to the earliest primates were not the warm tropical canopies of the textbook account but cold, seasonal woodlands at northern latitudes, where freezing winters and uneven food supply shaped the lineage from the start. That is according to a University of Reading team whose reconstruction of primate geography and climate places the common ancestor of all living primates in a cold North American climate rather than a stable equatorial forest.
“It turns out primates didn’t emerge from lush jungles,” said Jorge Avaria-Llautureo, the evolutionary biologist at the University of Reading who led the work, with his team reporting that the first primates instead came from cold, seasonal environments in the northern hemisphere. Published in the Proceedings of the National Academy of Sciences, the study overturns the warm-tropical-forest hypothesis that has guided evolutionary thinking for decades.
Reconstructions that combined evolutionary trees, fossil and living primate distributions, paleogeographic maps, and climate simulations identified North America as the ancestral home in eight of 10 main analyses and in all 100 median-dated trees. The team worked with 479 species across the record, 178 of them extinct and known only from fossils, with a model that restricted the common ancestor to North America preferred over the alternatives and recovered across 80 per cent of 200 datasets.
That cold label follows the Köppen-Geiger classification rather than any image of ice sheets, marking a climate whose warmest month clears 10 degrees Celsius while its coldest falls to or below freezing. Early primates on this reading occupied cold, temperate and dry climates well before tropical forests became central to the group, which the authors date to a later chapter of its history.
Applying a single climate standard across the fossil record, the team found that many sites long filed as tropical were in fact cool-mixed forests, which pulls the warm cradle out from under the standard account. Primates that crossed into a new climate travelled 561 kilometres on average, compared with 137 kilometres for those that stayed put, a spread the authors read as evidence that shifting forests kept forcing the group to move or die out.
Teilhardina, among the earliest primates the team traces, was a tree-dweller weighing 28 grams, the mass of the smallest primate alive today. A body that small and that bound to the canopy, sitting near the base of the group, keeps early primate life tied to the forest, whatever the climate those forests grew in.
“No primate relative has ever been found at such extreme latitudes,” said Kristen Miller, the University of Kansas researcher whose 2023 fossil study described two species of Ignacius from Ellesmere Island in Arctic Canada. Both primatomorphs lived 52 million years ago at a paleolatitude of 77 degrees north, in a warm-temperate swamp forest that still endured six months of winter darkness.
Miller’s team read the Ellesmere animals as strongly arboreal, living most of the time in the trees of that polar forest, yet larger and heavier-jawed than their southern kin. Teeth and jaws made for hard food mark a forest that yielded nuts and seeds through the dark months rather than the year-round fruit of an equatorial canopy.
Survival in those conditions may have leaned on torpor or hibernation, a metabolic slowdown that living dwarf lemurs still use and that the authors flag as one plausible tool for early primates facing long, foodless winters. Fossils record diet, body size and locomotion far more readily than metabolism, so the hibernation idea stays a reasoned possibility rather than a demonstrated fact for any extinct species.
The reclassification extends beyond primates, because the fossil sites it rests on also anchor how researchers picture northern forests deep in the past, a record that spans from the world’s oldest fossilised forest to the cold woodlands traced here. Tropical rainforest, on the study’s account, was a destination the group reached late rather than the home it began in, a sequence the authors trace across tens of millions of years of movement through northern climates.
Avaria-Llautureo puts the first primate at 66 million years ago and treats the cold-climate origin as the most contested finding of the work. Its northern signal held across all 100 median-dated trees the team ran, which, on his account, leaves the tropical-origin story so hard to defend.
For more information: Avaria-Llautureo J, Püschel TA, Meade A et al. “The radiation and geographic expansion of primates through diverse climates.” Proceedings of the National Academy of Sciences, 5 August 2025. DOI: 10.1073/pnas.2423833122. The Arctic fossil evidence appears in PLOS ONE: Miller K, Tietjen K, Beard KC. “Basal Primatomorpha colonised Ellesmere Island (Arctic Canada) during the hyperthermal conditions of the early Eocene climatic optimum.” PLOS ONE, 25 January 2023. DOI: 10.1371/journal.pone.0280114.
