Early primates evolved in cold climates, not tropical jungles

Sixty-six million years ago, North America saw long, dark winters. Fossils now suggest tiny primates were already there, coping with ice and snow.

A new analysis turns the usual tropical origin story on its head. The research combines hundreds of fossils with climate models to track primate ancestors through time.

“Our findings flip that narrative entirely,” said Jorge Avaria-Llautureo, an evolutionary biologist at the University of Reading. His team traced the primate family tree back to chilly northern forests.

Primates adapted to freezing climates

The team worked with the Köppen-Geiger climate system, a scheme that sorts environments by average heat and rain. Their maps place the earliest true primates in a zone with hot summers and sub-freezing winters.

That habitat fits today’s upper Midwest more than a steamy jungle. It means our lineage started where annual temperature swings could reach 70 degrees Fahrenheit.

These ancestors likely looked like nimble squirrel-sized creatures. They foraged at night, avoiding daytime chill.

Statistical models show a 70% chance that the first crown primates lived in what is now North America, with 30% pointing to Western Europe – territories then sitting near 45° N before plate motion. Their later travels reflect how moving land and changing skies steered evolution.

Fossils reveal primate movement

Fossils alone cannot solve the puzzle because they capture animals only where sediments preserve bones. The new study adds computer methods that simulate how species move across shifting landmasses.

By feeding 902 living and extinct species into BayesTraits software, the group estimated branch-by-branch journeys. They then matched positions with climate layers produced by the Hadley climate model.

The results indicate that early primates stayed in cold or temperate zones for at least 18 million years. Tropical forests entered the picture much later.

Warmer global temperature spikes such as the Paleocene-Eocene Thermal Maximum did not speed their spread. Instead, local temperature swings mattered most.

Early primates made long journeys

When ancestral lineages ventured into new climate categories, they tended to roam farther. Major moves often involved crossing climate boundaries rather than continents.

Median treks reached roughly 349 miles, compared with 85 miles for moves within familiar conditions. The bigger jumps exposed populations to novel habitats and pressures.

Such leaps helped generate new species by separating kin groups long enough for them to drift apart genetically. The pattern echoes broad ecological models that link dispersal to diversification.

Independent work on North American mammals predicts roughly 9 % of species will fail to outrun current warming trends, underlining the cost of slow feet. Swift past wanderers hint at which modern lineages could thrive.

How primates survived cold

How could small primates endure months of scarce food and sub-freezing nights? One answer is hibernation, a state in which body temperature and metabolism plunge.

Today’s dwarf lemurs in Madagascar sleep underground for up to seven months each year, a strategy first documented in 2004.

Later fieldwork showed that other dwarf lemur species also hibernate when mountain air turns icy.

These living examples show that primate physiology can slow to bear-like torpor, supporting the idea that ancient relatives did something similar.

Fast climate shifts caused changes

The Reading group found that the rate, not the direction, of local change predicted primate success. Rapid swings in heat or rain pushed species to travel or perish.

That insight matters today because many forests are shifting faster than ever measured. Flexible species may cope, while specialists could hit a wall.

The study also separates global averages from local reality. A place can warm overall yet still see harsher cold snaps or erratic storms that jar wildlife.

Conservation planners often model future ranges with coarse climate grids. The new work argues for finer, neighborhood-scale maps.

Old origin ideas were wrong

Textbooks have long tied primate origins to lush equatorial canopies. That view leaned on early fossil finds labeled “paratropical” without rigorous climate checks.

By applying a single classification standard, the team showed that many supposed rain-forest sites were actually cool mixed forests.

The conclusion challenges popular origin theories like “visual predation,” which assume dense, warm vegetation shaped grasping hands and forward eyes. Those traits may have first evolved among conifers instead.

The researchers also found that rosid plants, common in temperate woods, diversified around the same time, offering fruit and sap to budding primates.

Primates adapted to shifting climates

Early primates were tougher and more mobile than usually portrayed. They met freezing dawns, marched hundreds of miles, and only later settled in the tropics where most descendants remain.

Their story suggests resilience has always underpinned primate history, yet it came with extinctions for lineages that failed to keep pace.

Modern humans, one branch of that hardy clan, now drive the climate engine. Understanding our icy roots may remind us how quickly fortune can flip.

The study is published in Proceedings of the National Academy of Sciences.

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