LATE QUATERNARY HISTORY OF THE NORTHERN BEETLE FAUNA OF NORTH AMERICA: A SYNTHESIS OF FOSSIL AND DISTRIBUTIONAL EVIDENCE

Fossils from sites of Late Quaternary age in North America provide tangible evidence of temporal changes in the character of the northern beetle fauna. Based on a synthesis of the fossil data with analyses of the present distributions for northern species, a rudimentary model is proposed to explain the recent history of the fauna of the arctic and the boreal forest.An open-ground beetle fauna of arctic–subarctic affinities had become established along the southern margin of the Laurentide ice sheet in the midcontinent by 20 500 years before present (yr B.P.). Climatic warming decimated this fauna throughout lowland areas at some time between 16 700 and 15 300 yr B.P.; small populations of some arctic–subarctic species, however, survived within either alpine habitats of the Cordillera and Appalachians or specialized environments associated with stagnant ice.Populations of the same arctic–subarctic beetle species existed within the ice-free Alaska–Yukon refugium throughout the late Wisconsinan. During the Holocene, this region served as the principal centre-of-origin for the dispersal of the arctic–subarctic beetle fauna.The beetle fauna of the boreal forest was also displaced southward by Late Wisconsinan glaciation. By 15 300 yr B.P., however, this fauna had largely replaced the arctic–subarctic beetle fauna along the ice margin of the midcontinent. Evidence provided by fossils from a series of sites demonstrates that beetle species of the boreal forest dispersed northward into Canada as the ice front receded.