28 Curtis C. Bentley and James L. Knight 



equable climate than today prevailed near or during the maximum advance of the 

 Laurentide ice sheet in the southeastern United States. 



Based on the distribution of terrestrial vertebrates, Smith (1957) stated 

 that the northeastern biota of North America was displaced southward during the 

 Wisconsinan glacial maximum. Smith also suggested that during a "Climatic 

 Optimum," southern counterparts dispersed northward. During the height of the 

 Wisconsinan glaciation, E. blandingii would have been extirpated from its pre- 

 sent-day northerly distribution (Mickelson et al. 1983, Conant and Collins 

 1991). The southern boundary of the Laurentide ice sheet, while abutted against 

 the Appalachian Plateau (Mickelson et al. 1983), could potentially have forced 

 the range of E. blandingii to be split, with one population occurring along the 

 Mississippi Valley and another along the Atlantic Coastal Plain. This may have 

 produced geographically isolated eastern and western populations of Emydoidea 

 blandingii during the late Pleistocene. 



In addition to Emydoidea blandingii, Spermophilus tridecemlineatus 

 (thirteen-lined ground squirrel) was also collected from the Ardis site (Bentley et 

 al. 1994). Based on Recent and fossil distributions (Kurten and Anderson 1980), 

 the present northeastern distribution of the thirteen-lined ground squirrel also 

 may have been displaced southward along the Atlantic Coastal Plain by the 

 advancing Laurentide ice sheet. 



As with the Gulf Coast Corridor, depressed sea levels during the Pleis- 

 tocene glacial stage exposed much or all of the Atlantic continental shelf (Bloom 

 1983), thereby widening the Atlantic Coastal Plain. This may have facilitated 

 the dispersal of glacially-displaced species southward along the coast. The 

 newly emergent land area provided expanded habitats for species to utilize 

 (Blaney 1971), and a more equable climate may have allowed for the range 

 extention of both northern and southern species into these new areas. Northern 

 populations of T. c. Carolina in Massachusetts and Michigan that show affinity to 

 T. c. major, discussed by Milstead (1969), may be relicts left over from a Pleis- 

 tocene interval of extensive intergradation between the northerly displaced sub- 

 species and radiating southern subspecies. 



Bleakney (1958) suggested that the Recent population of E. blandingii 

 in Nova Scotia survived glaciation in an "Atlantic Coastal Plain refuge" and then 

 dispersed northward up the coast into Canada and Maine. Preston and McCoy 

 (1971), suggested that "colonization of the Atlantic Coastal Plain from the Great 

 Lakes region, along a 'steppe corridor' (Schmidt 1938) through the Mohawk 

 Valley" was a more plausible hypothesis. Preston and McCoy (1971) also stat- 

 ed that the study of specimens from the eastern limits may provide an answer to 

 the possibility of a "minor Atlantic Coast refuge for Emydoidea during ice 

 advances." The presence of numerous E. blandingii at the Ardis site, as well as 

 fossil material from New Trout Cave in West Virginia (Holman and Grady 1987), 

 suggest that the Recent extreme northeastern populations may be products of a 



