Recent development of the Mutual Climatic Range (MCR) technique of paleotemperature reconstruction for use in Alaska and the Yukon Territory led to the creation of climate envelopes for about 250 species found in Late Pleistocene fossil assemblages in this region (Eastern Beringia). Working with John Matthews (Geological Survey of Canada, retired), the author was able to apply the MCR method to Late Tertiary and Early Quaternary beetle assemblages from Alaska, the Yukon, and the Canadian high arctic archipelago. About 95% of the species in assemblages dating from ca. 7,000,000 to 500,000 years ago remain extant. The MCR method was sucessful in yielding results from these assemblages.

Our estimates were generally compatible with previous paleobotanical reconstructions, but we were able to quantify our results, and to estimate both mean summer and winter temperature regimes. Late Tertiary seasonal temperatures were substantially warmer than present, and there was significantly less latitudinal difference in temperature than in seen today. Early Quaternary assemblages show the dramatic temperature decline associated with the onset of Pleistocene glaciations.