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


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Publication Date

January 1853


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.




U.S. Geological Survey Bulletin, Vol. 1853 (1853).