A species surviving from an ancient time in isolated populations that represent the localized remains of a distribution which was originally much wider. These populations become isolated through disruptive geophysical events such as glaciation , or immigration to outlying islands, which is not followed by reunification of the fragmented populations. The origins and relationships of several relict species are well documented, and these include local Central American avian populations which are remnants of the North American avifauna left after the last glacial retreat. The origins of other relict species are unknown because all related species are extinct. This group includes lungfishes, rhynchocephalian reptiles (genus Sphenodon ), and the duck-billed platypus (Ornithorhynchus anatinus ).