Descendants of a common ancestor in some cases inhabit different continents and also differ from each other This is called discontinuous distribution. Common example is of alligators which at present occur only in South-eastern United States and Eastern China. Such a discontinuous distribution can be explained as follows : Bering Strait Region. The climate of the whole region was much warmer than at present , and the alligators (as revealed by fossil evidence ) were distributed over the entire region. In late Cenozoic , the climatic changes, due to ice age, caused extinction of alligators in most of the region. South-eastern United States and Eastern China remained by glaciations and here the alligators survived. The alligators of these regions have been separated for a long time, and have developed different random mutations. As a result , they have become slightly different but closely species of the same genus
