Researchers at several Colorado universities say ancient ancestors of rhinos and pig-like tapirs were able to eke out a living in the Arctic Circle 53 million years ago, despite six months of winter darkness. Back then, the Arctic appears to have been much milder than it is now--a bit like Colorado's weather, with forests that provided food such as flowering plants in the summer and twigs and evergreen needles in the winter,Â United Press International  reports. The study provides clues into how the world looked millions of years ago as well as how animals might adapt and migrate if Earth's climate continues to warm, writesÂ U.S. News & World Report . Authored by University of Colorado at Boulder professor Jaelyn Eberle (pictured), Henry Fricke of Colorado College in Colorado Springs, and John Humphrey of the Colorado School of Mines in Golden, the study analyzed the animals' fossilized teeth to discern their eating habits in order to rule out that they either hibernated or migrated to escape the Arctic's winter shroud. Eberle, who is also curator of fossil vertebrates at CU's Museum of Natural History, tells theÂ Daily Camera , "This study may provide the behavioral smoking gun for how modern groups of mammals like ungulates--ancestors of today's horses and cattle--and true primates arrived in North America."