U.S. scientists have determined how high arctic mammals lived about 54 million years ago in a study said to be important in view of Earth's climate change.

University of Colorado-Boulder researchers said ancestors of tapirs and ancient cousins of rhinos living above the Arctic Circle 53 million years ago endured six months of darkness each year in a mild climate that featured lush, swampy forests.

Assistant Professor Jaelyn Eberle, who led the researchers, said the study shows several varieties of prehistoric mammals lived on what is today Ellesmere Island near Greenland on a summer diet of flowering plants, deciduous leaves and aquatic vegetation. But in winter's twilight, the mammals apparently switched to foods like twigs, leaf litter, evergreen needles and fungi.

Eberle, curator of fossil vertebrates at the University of Colorado Museum of Natural History, said the findings have implications for modern mammals that likely will begin moving north if Earth's climate continues to warm.

A paper on the subject co-authored by Henry Fricke of Colorado College and John Humphrey of the Colorado School of Mines appears in the journal Geology.