Paleoendemism along with neoendemism is one of two sub-categories of endemism. Paleoendemism refers to species that were formerly widespread but are now restricted to a smaller area. Neoendemism refers to species that have recently arisen, such as through divergence and reproductive isolation or through hybridization and polyploidy in plants.
It is not always clear whether a particular species is paleoendemic or neoendemic. For example, kiwis, which are confined to New Zealand, were cited as examples of paleoendemism, but this seems to have been an error. Kiwis belong to the ratites (a group of flightless birds). Because most parts of the former supercontinent Gondwana have ratites, or did have until the fairly recent past, the traditional account of ratite evolution has the group emerging in flightless form in Gondwana in the Cretaceous, then evolving in their separate directions as the continents drifted apart. More recently, it has been suggested that ratites lost the ability to fly multiple times, and the proto-kiwi developed an inability to fly after arrival in New Zealand. “Overwater dispersal” has been hypothesised for the arrival of the kiwis' ancestor in New Zealand.