Term for the "one line of descent" origin of birds [or animals]. According to Mayr (1942), it means "descendants of a single interbreeding group of populations, in other words, descendants of a single species.".
^Mayr, E. (1942). Systematics and the origin of species. New York: Columbia University Press.
^Terres, John K. (1980). The Audubon Society Encyclopedia of North American Birds. Alfred A. Knopf, Inc. ISBN0394466519.