Tail-length evolution in Fascicularis-group macaques (Cercopithecidae: Macaca)

In the four species of macaques that constitute the fascicularis-group, relative tail length generally decreases with increasing latitude, in accord with Allen's Rule Although this generalization applies to Macaca mulatta ire the northern part of its range-north of ca. 26 degrees N, it does not apply south of ca. 26 degrees N, where the tail is anomalously short in Macaca mulatta. This suggests that the anomalously short-tailed population of Macaca mulatta did not originate within its present latitudinal range, but instead dispersed there from farther north. The anomalously short-tailed population apparently replaced a now-extinct longer-tailed population, from which founders of insular Macaca cyclopis previously had been derived. Southward dispersal of the anomalously short-tailed population of Macaca mulatta, and correlated extinction of the longer-tailed population that it apparently replaced, may have been induced by a major glacial advance.