Of Mice and Ice in the Late Pliocene of North America

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 600,000 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 850,000 years ago.

Pliocene and Pleistocene geologic and climatic evolution in the San Luis Valley of south-central Colorado

Sediments of the Alamosa Formation spanning the upper part of the Gauss and most of the Matuyama Chrons were recovered by coring in the high (2300 m) San Luis Valley of south-central Colorado. The study site is located at the northern end of the Rio Grande rift. Lithologic changes in the core sediments provide evidence of events leading to integration of the San Luis drainage basin into the Rio Grande. The section, which includes the Huckleberry Ridge Ash (2.02 Ma) and spans the entire Matuyama Chron, contains pollen, and invertebrate and vertebrate fossils. Stable isotope analyses of inorganic and biogenic carbonate taken over most of the core indicate substantially warmer temperatures than occur today in the San Luis Valley. At the end of the Olduvai Subchron, summer precipitation decreased, summer pan evaporation increased, and temperatures increased slightly compared to the earlier climate represented in the core. By the end of the Jaramillo Subchron, however, cold/wet and warm/dry cycles become evident and continue into the cold/wet regime associated with the deep-sea oxygen-isotope Stage 22 glaciation previously determined from outcrops at the same locality. Correspondence between the Hansen Bluff climatic record and the deep-sea oxygen-isotope record (oxygen-isotope stages from about 110-18) is apparent, indicating that climate at Hansen Bluff was responding to global climatic changes.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/29956/1/0000316.pd

Of Mice and Ice in the Late Pliocene of North America

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 600,000 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 850,000 years ago.

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

The Cheetah Room fauna of Hamilton Cave, West Virginia, is a full complement of vertebrates including microtine rodents. The microtines are represented by a new species of the subgenus Mimomys (Cromeromys) that was formerly known only from Eurasia, a new species of Phenacomys similar toP. albipes, Allophaiomys p/iocaenicus, Lasiopodomys deceitensis that was formerly known only from the arctic region, Microtus paroperarius, Pitymys hibbardi, Ondatra annectens, a bog lemming intermediate between the genera Mictomys and Synaptomys, and Atopomys salve/in us. The transitional morphologic variations, between ancestor and descendants, of Phenacomys, the bog lemming, and Pitymys hibbardi, as well as the presence of Microtus paroperarius, are the principal reasons for an age assignment of between 740,000 and 850,000 years. The history of the bog lemmings begins 4 million years ago in southeastern Europe with Plioctomys mimomiformis, of unknown ancestry. This species dispersed eastward across Asia to Beringia, where its youngest record is 2.4 million years old; during this first 1.6 million years of the history there was no detected morphologic change in the dentition. However, between 3 and 2.6 million years ago these bog lemmings also dispersed southward from Beringia to the United States on both sides of the Rocky Mountains, during which dispersal they evolved east of the cordillera into a new species, Plioctomys rinkeri, and to the west into a new genus and species, Mictomys vetus. By 2.0 million years ago Mictomys spread eastward around the southern end of the Rocky Mountains and Plioctomys became extinct. More than 1 million years later Synaptomys abruptly evolved out of a southeastern population of Mictomys in one of the more remarkable morphologic transitions known in vertebrate paleontology, as recorded in the Cheetah Room fauna

The chronologic and geographic range of desmostylians

Volume: 78Start Page: 1End Page: 2

Vertebrate fossils and their context : contributions in honor of Richard H. Tedford. Bulletin of the AMNH ; no. 279

vii, 659 p. : ill. (2 col.), maps ; 26 cm.Includes bibliographical references.Foreword / Michael J. Novacek -- 1. Richard H. Tedford : field man, systematist, professor, and mentor / Michael O. Woodburne, Robert M. Hunt, Jr., Gina C. Gould, Eugene S. Gaffney and Lawrence J. Flynn -- 2. Dispersals of Neogene carnivorans between Asia and North America / Qiu Zhanxiang -- 3. Pinnipedimorph evolutionary biogeography / Thomas A. Deméré, Annalisa Berta and Peter J. Adam -- 4. Intercontinental migration of large mammalian carnivores : earliest occurrence of the Old World beardog Amphicyon (Carnivora, Amphicyonidae) in North America / Robert M. Hunt, Jr. -- 5. Notes on early Oligocene ursids (Carnivora, Mammalia) from Saint Jacques, Nei Mongol, China / Wang Banyue and Qiu Zhanxiang -- 6. New procyonines from the Hemingfordian and Barstovian of the Gulf Coast and Nevada, including the first fossil record of the Potosini / Jon A. Baskin -- 7. Pack hunting in Miocene borophagine dogs : evidence from craniodental morphology and body size / Blaire Van Valkenburgh, Tyson Sacco, and Xiaoming Wang -- 8. New material of Osbornodon from the early Hemingfordian of Nebraska and Florida / Xiaoming Wang -- 9. Carnivora (Mammalia, Felidae, Canidae, and Mustelidae) from the earliest Hemphillian screw bean local fauna, Big Bend National Park, Brewster County, Texas / Margaret Skeels Stevens and James Bowie Stevens -- 10. Chronostratigraphy, biochronology, datum events, land mammal ages, stage of evolution, and appearance event ordination / Everett Lindsay -- 11. New late Uintan to early Hemingfordian land mammal assemblages from the undifferentiated Sespe and Vaqueros formations, Orange County, and from the Sespe and equivalent marine formations in Los Angeles, Santa Barbara, and Ventura counties, southern California / David P. Whistler and E. Bruce Lander -- 12. Mammalian biochronology of Blancan and Irvingtonian (Pliocene and early Pleistocene) faunas from New Mexico / Gary S. Morgan and Spencer G. Lucas -- 13. Mexico's Middle Miocene mammalian assemblages : an overview / Ismael Ferrusquía-Villafranca -- 14. New evidence of Miocene Protoceratidae including a new species from Chiapas, Mexico / S. David Webb, Brian Lee Beatty and George Poinar, Jr. -- 15. New oreodont (Mammalia, Artiodactyla) from the late Oligocene (early Arikareean) of Florida / Bruce J. MacFadden and Gary S. Morgan -- 16. Craniodental analysis of Merychippus insignis and Cormohipparion goorisi (Mammalia, Equidae), Barstovian, North America / Michael O. Woodburne -- 17. Mimomys in North America / Charles A. Repenning -- 18. Dasyurids, perameloids, phalangeroids, and vombatoids from the early Pliocene Hamilton fauna, Victoria, Australia / William D. Turnbull, Ernest L. Lundelius, Jr. and Michael Archer -- 19. A new species of Muramura Pledge (Wynyardiidae: Marsupialia) from the Middle Tertiary of the Callabonna Basin, northeastern South Australia / Neville S. Pledge -- 20. The strange case of the wandering fossil / Thomas H. Rich, Thomas A. Darragh and Patricia Vickers-Rich -- 21. Oligocene/Miocene beds and faunas from Tieersihabahe in the northern Junggar Basin of Xinjiang / Ye Jie, Meng Jin and Wu Wenyu -- 22. Rodents from the Chinese Neogene : biogeographic relationships with Europe and North America / Qiu Zhuding and Li Chuankuei -- 23. Tedford's gerbils from Afghanistan / Lawrence J. Flynn, Alisa J. Winkler, Louis L. Jacobs and Will Downs, III -- 24. Another molar of the Miocene hominid Griphopithecus suessi from the type locality at Sandberg, Slovakia / Peter Holec and Robert J. Emry -- 25. Mimotricentes tedfordi, a new arctocyonid from the late Paleocene of California / Malcolm C. McKenna and Donald L. Lofgren -- 26. Phosphatochelys, a new side-necked turtle (Pelomedusoides: Bothremydidae) from the Paleocene of Morocco / Eugene S. Gaffney and Haiyan Tong