Response of pocket gophers (<i>Geomys</i>) to late Quaternary environmental change on the Edwards Plateau of central Texas

Abstract

Fossils of pocket gophers (Geomys) recovered from Hall's Cave, Texas, comprise a large sample of specimens spanning the late Pleistocene through Holocene. Statistically adequate sample sizes, a well-constrained chronology and independent palaeoenvironmental data allowed for the testing of both taxonomic change and predictions of ecophenotypic change in the dentary of Geomys. A time-transgressive reduction of diastema length (DL) in Geomys was predicted based on known, regional palaeoenvironmental changes and known ecophenotypic response in the closely related genus, Thomomys. Statistical evaluation suggests that although DL in Geomys is correlated to tooth row length (TRL), changes in DL may reflect an independent ecophenotypic response. Testing was hampered by the inadequacy of TRL as a diagnostic feature of most Geomys from Texas. A statistical test using coefficient of variation revealed the presence of multiple species of Geomys in some stratigraphic levels. Reduced local richness of Geomys to a single species coincides with the loss of other burrowing taxa in the vicinity of Hall's Cave. Based on the results of an analysis of variance (ANOVA) test, no significant changes in DL occurred in populations of Geomys from Hall's Cave.