Paleoenvironmental change and the microevolution of muskrat from Lubbock Lake

The struggle for survival in the face of a changing environment often is dramatic and obvious. The dinosaurs failed to adapt and became extinct at the beginning of the Cretaceous, for example, while the mammals radiated and diversified (Raup, 1988). Not all evolution, however, occurs on such a grand scale and with such profound implications. Evolution also takes place on small scales (Brandon, 1990). While these small struggles may have little or no implication for future species, if preserved in the fossil record they can still serve an important purpose. These records yield information about the forces that drive adaptation £ind speciation on large scales (Mayr, 1976). While the evidence of evolution may take many forms, it is commonly found in the physical remains of organisms caught in the process of adapting to changing environmental conditions. The fossil remains, then, may be interpreted to reveal the nature of the stmggle. This battle for survival has been recorded in the subfossil muskrats (Ondatra aibethicus) of Lubbock Lake.