Herpetological Population Adjustments in the Pleistocene of Britain and Europe

Abstract

Compared to herpetological population adjustment patterns in North America (sec Holman, 1995c), the patterns in Britain and central and northern Europe seem to be rather straightforward. Basically, (1) very few herpetological species were present in ice-free areas during full glacial times, and (2) formerly glaciated areas were reinvaded by species from the south during warming cycles. Moreover, during climatic optimal warm times, several southern species existed well north of their present ranges. The invasion of southern Europe by northern populations in cold times is taken for granted (e.g., Rocek, 1995), although, as addressed in this chapter, it is difficult to document this in the fossil record. As indicated by geological and fossil evidence, the British Islands were connected to continental Europe during much of the Pleistocene. Although sea level changes in the British late Pleistocene arc a subject of some controversy (Stuart, 1982), it is generally agreed that Britain first separated from Ireland and then from the continent early in the Holocene. The classic idea is that the very depauperate British heretofauna of the cold part of the Devensian (last glacial stage) became somewhat, but not fully enriched by herpetological species during a warming trend that began about 10,000 ybp and lasted until about 8,500 ybp. The fact that Ireland has a much poorer modern herpetofauna (Triturus vulgaris, the rare Bufo calamita, Rana temporaria, and Lacerta vivipara) than Britain, which has six native species of amphibians and six native species of reptiles (Fra/,er, 1983; Smith, 1964), is attributed to Ireland's early separation from Britain. The Irish herpetofauna suggests that this separation occurred rather soon after the final withdrawal of the Devensian (last glacial) ice sheet. One of the most common questions asked about snakes, especially near St. Patrick's Day, is, "Have there ever been any snakes in Ireland?" No fossil snakes have ever been found in Ireland. But since Ireland lacks a terrestrial fossil record during most of the time that snakes have existed, it would seem that snakes could have lived in Ireland during some part of geological time. As far as I am aware, the few Pleistocene deposits containing herpetological remains in Ireland represent very late Devensian (last glacial) times.