The microtine rodents of the Cheetah Room fauna, Hamilton Cave, West Virginia, and the spontaneous origin of Synaptomys

Between 2.5 to 1.8 million years ago changes in arctic climate and in meadow mouse dispersal routes correlate with part of the history of uplift and glacial erosion of the Chugach and Saint Elias mountains in Alaska and adjacent Canada. Earlier meadow mice dispersing from Asia to central North America followed a southward coastal route between these mountains and the Pacific Ocean, appearing first in the United States Pacific Northwest. Two and a half million years ago, accelerated uplift of the Chugach and Saint Elias mountains milked Pacific westerly winds, enlarging the ice fields in these mountains so that they then flowed to the sea. This blocked the coastal dispersal for 600 O00 years, when no new immigrant meadow mice appeared in the conterminous United States. The uplift also restrained westerly winds that crossed Canada, permitting moister air from the subtropical Atlantic and from an unfrozen Arctic Ocean to produce significant continental glaciation, centered in eastern Canada. By 2.0 million years ago, glacial erosion had lowered these mountains again, letting relatively dry Pacific westerlies extend across Canada, reducing the encroachment of moist Atlantic and arctic air, and ending continental glaciation to the east. The simultaneous reduction of glacial activity in the cordillera allowed meadow mice to renew southward dispersal. Additionally, the lowered mountains remained a rain shadow, causing grassland in the Great Plains of Canada. Thus a new dispersal route to the United States was opened for grazing meadow mice and for the first time their earliest records were in the Great Plains. Loss of the continental ice sheet and an unfrozen Arctic Ocean facilitated the northward spread of warm and moist air from the North Atlantic subtropical high; it flowed northward up the eastern front of the Rocky Mountains in the United States and, mingling with the dry westerlies, northeastward across Canada to northernmost Greenland, where trees then grew. About 1.8 million years ago the Great Plains of the United States were subtropical savannah and remained so until the beginning of the Ice Age 850 O00 years ago.

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Late Pliocene-early Pleistocene ecologic changes in the Arctic Ocean borderland

Repenning¹,

Brouwers²

1992

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BORDERLAND extended as far north as the northernmost point of Greenland, lat 82°30' N. and about mi (800 km) south of the North Pole. Faunal and floral records at lower latitudes in North America and Europe indicate warmer temperatures and increased precipitation at this time. The beginning of the second cycle of cooling is not sharply marked. Near the end of the Olduvai Normalpolarity Subchron (about 1.7 m.y. ago), proxy evidence in Europe and North America indicates that the extreme warmth in the Arctic Ocean Borderland had ended. Faunal, floral, and depositional records from the Arctic Ocean, Europe, and North America indicate an oscillation of cool and warm periods between 1.7 and 1.2 million years ago. Both Arctic and Atlantic oceanic temperatures suggest that average conditions were similar to those of today, but the Arctic Ocean was not perennially ice covered. The severity of the cold periods increased, and about 1.1 million years ago the Arctic Ocean again began to have periods of perennial ice cover. A cold and dry climate, more severe than today, is indicated in western Beringia at this time, and the abundance of arboreal plants was at a minimum. This cold climate was recorded as far south as the Netherlands; however, less than 100,000 years later, during the Jaramillo Normal-polarity Subchron, the pollen spectrum of eastern and western Beringia was similar to that of today, if not somewhat warmer. About 850,000 years ago, ice again flowed down the Mississippi River Valley, beginning the Ice Ages in the United States, and bottom sediments in the Arctic Ocean indicate that perennial ice cover was more frequent. Although the Ice Ages began 850,000 years ago, climatic deterioration apparently did not reach its extreme until about 400,000 years ago.

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The microtine rodents of the Cheetah Room fauna, Hamilton Cave, West Virginia, and the spontaneous origin of Synaptomys

Cited by 4 publications

References 7 publications

West European arvicolid evidence of intercontinental connections during the Early Pleistocene

West European arvicolid evidence of intercontinental connections during the Early Pleistocene

Of Mice and Ice in the Late Pliocene of North America

Late Pliocene-early Pleistocene ecologic changes in the Arctic Ocean borderland

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