Global Warming Causes

KNOWN GEOGRAPHIC AND TEMPORAL DISTRIBUTION Olt

See "Known Geographic and Temporal Distribution" sections for Mictomys vetus or M. landesi and Mictomys kansasensis or M. meltoni.

ALLOPHAIOMYS PLIOCAENICUS KORMOS, 1933

IDENTIFICATION Molars are rootless; the m1 consists of a posterior loop, three alternating closed triangles, and well-developed primary wings (triangles 4 and 5; terminology following Repenning, 1992) that are broadly confluent with a very simple anterior cap. Only m1s are identifiable as Allophaiomys.

TAXONOMIC background The complicated Old and New World history of Allophaiomys was reviewed by Repenning (1992) and Martin and Tesakov (1998a). Fossils are reported from across much of the Holarctic; traditionally these fossils were considered to represent one or two extinct species with an extremely wide geographic distribution. Recent analyses of large samples of Allophaiomys, especially from Europe, indicate that the evolutionary history may be much more complex and that multiple closely related species may be erroneously assigned to a single taxon (Agusti, 1992; Agusti et al., 1993; Nadachowski and Zagorodnyuk, 1996; Martin and Tesakov, 1998b; Nadachowski and Garapich, 1998). A growing body of evidence strongly suggests that an Allo-phaiomys morphotype was present ancestrally in several, and perhaps many, early lineages of arvicolines allied to the extant genus Microtus (sensu lato). These morphotypes persist in populations of several extant, Old World arvicoline species (Nadachowski and Zagorodnyuk, 1996; Nadachowski and Garapich, 1998) but are no longer found among North American species.

The status of the North American fossils with an Allo-phaiomys morphotype is not certain, but the traditional conceptualization was that Allophaiomys in North America gave rise to multiple independent lineages that still have extant representatives in the North American fauna (e.g., Martin, 1975; Repenning, 1992; Martin and Tesakov, 1998b). In light of this interpretation, we find perplexing the direct strati-graphic association of AHophaiomys with several of its purported descendants (Microtus meadensis, M. paroperarius, and Microtus sp. with five closed triangles on ml) in the Pit fauna (Bell and Barnosky, 2000) and the CM Velvet Room excavation (level 3) in Porcupine Cave, and in Cathedral Cave (Bell, 1995; Bell and Barnosky, 2000).

A recent phylogenetic analysis of 24 Microtus species based on mtDNA sequence data (Conroy and Cook, 2000) resulted in recognition of a monophyletic North American clade of endemic Microtus species. This result challenges the traditional hypothesis that the diversity of extant North American Microtus species is the result of multiple independent dispersal events from Asia via the Bering Land Bridge. These data provide an interesting challenge for paleontologists seeking to unravel the complexities of arvicoline evolution and bio-geography in North America because they suggest that all extant, endemic North American Microtus species are descended from a single common ancestor.

It is not clear what this means for interpreting the taxo-nomic, much less the phylogenetic, status of populations traditionally referred to AHophaiomys. The recommendation to refer all AHophaiomys morphotypes to the genus Microtus (Martin, 1987) seems premature, and treatment of AHophaiomys as an arbitrarily defined "metaregion" as suggested by Martin and Tesakov (1998b) offers little in the way of resolution to the problem. We continue to refer these North American morphotypes to the nominal species A. pliocaenicus, but we acknowledge that this is a somewhat arbitrary assignment.

DISTRIBUTION WITHIN PORCUPINE CAVE DMNH 942, Badger Room; UCMP V98022, Fissure Fill A; DMNH 1347, Generator Dome; UCMP V93174, Gypsum Room; UCMP V93173, Pit; UCMP V93175, CM Velvet Room; DMNH 644, DMNH Velvet Room; DMNH 1349, Mark's Sink.