have been identified by their skull morphology and limb morphology to be Beringian wolves have been found in the Natural Trap Cave at the base of the Bighorn Mountains in Wyoming, United States. These were radiocarbon dated to between 25,800 and 14,300YBP, and this location is directly south of what would at that time have been the division between the Laurentide Ice Sheet and the Cordilleran Ice Sheet. This suggests that a temporary channel existed between the glaciers from 25,800YBP until the advance of the ice sheets 16,000–13,000YBP. The migration of the Beringian wolf southwards is assumed to have been the result of pursuing prey species, as this cave also contained specimens of steppe bison that had migrated from Beringia and would have been prey for wolves, and muskox that is known to be an important prey species of the Beringian wolf. Dire wolves were absent north of 42°N latitude in the Late Pleistocene; therefore, this region would have been available for Beringian wolves to expand southwards. There is no evidence of expansion beyond this region. Extinction Extinction is the result of the elimination of the geographic range of a species with a reduction of its population size down to zero. The factors that affect biogeographic range and population size include competition, predator-prey interactions, variables of the physical environment, and chance events. Phenotype is extinct A phenotype is any observable and measurable characteristic of an organism and includes any morphological, behavioral, and physiological traits, with these characteristics being influenced by genes and the environment. The mammoth steppe lasted for 100,000 years without change until it came to an end around 12,000 years ago. The American megafaunal extinction event occurred 12,700YBP when 90genera of mammals weighing over became extinct. The extinction of the large carnivores and scavengers is thought to have been caused by the extinction of the megaherbivore prey upon which they depended. The cause of the extinction of this megafauna is debated but has been attributed to the impact of climate change, competition with other species, including humans, or a combination of both factors. For those mammals with modern representatives, ancient DNA and radiocarbon data indicate that the local genetic populations were replaced by others from within the same species or by others of the same genus. Postglacial environmental change throughout eastern Beringia brought about wholesale changes in vegetation, the regional extinction of much of the megafauna, and the