Climate tied to horse extinction

A changing climate, rather than hunting, may have led to the extinction of Alaska's native horses.

Horses evolved in Asia and are thought to have originally crossed the Bering land bridge to Alaska.

Scientists say about 70 per cent of North American large mammals became extinct between 20,000 and 10,000 years ago. Horses were part of the die-off.

Some blame hunting, but the possible reasons for the extinction are contentious.

Dale Guthrie, of the University of Alaska in Fairbanks, thinks climate change and a shift from grasslands to tundra is likely to blame because it would have reduced the animals' food supply.

"Horses underwent a rapid decline in body size before extinction and I propose that the size decline and subsequent regional extinction ... are best attributed to a coincident climate/vegetation shift," he wrote in Thursday's issue of the journal Nature.

Guthrie radiocarbon-dated bones from two species of extinct Alaskan horses. The bones date back about 12,500 years 500 years before the first signs of human settlement in the area.

The bones were about 12 per cent shorter than those from another horse that lived nearly 15,000 years earlier, he found.

"The present data do not support human overkill and several other extinction causes," Guthrie said.

He concludes a combination of influences likely led to the equine disappearance.

Spaniards reintroduced horses to the Americas in the 1500s.