An important distinction must be made between true extinction and extirpation. Extirpation is the loss of a population, or loss of a species from a particular geographic region. A famous twentieth-century example is the extirpation of wolves from the Yellowstone region of Wyoming. The park service reintroduced wolves to Yellowstone in the 1990s, and these predators appear to be adapting well to their new home. True extinction must also be differentiated from pseudoextinction. Biologists studying the changes that take place in a lineage over time often designate distinct morphological stages as separate species. The extinction of a species in this context is not the result of the termination of a lineage, but rather the transformation into a new form.

Wall, W. P. (2002). Extinction. In R. Robinson (Ed.), Biology (Vol. 2, pp. 64-67). New York: Macmillan Reference USA. Retrieved from http://link.galegroup.com/apps/doc/CX3400700162/GVRL?u=61wa_corpus&sid=GVRL&xid=f2282447