Evolution
There is evidence that ancestors of the fisher migrated to North America during the Pliocene era between 2.5 and 5 million years ago. Two extinct mustelids M. palaeosinensis and M. anderssoni have been found in eastern Asia. The first true fisher, M. divuliana, has been found only in North America. There are strong indications that M. divuliana is related to the Asian finds, which suggests a migration. M. Pennanti has been found as early as the Late Pleistocene era about 125,000 years ago. There are no major differences between the Pleistocene fisher and the modern fisher. Fossil evidence indicates that the fisher's range extended farther south than it does today.
Three subspecies were identified by Goldman in 1935, M.p. columbiana, M.p. pacifica, and M.p. pennanti. Later research has debated whether these subspecies could be positively identified. In 1959, E.M. Hagmeier concluded that the subspecies are not separable based on either fur or skull characteristics. Although some debate still exists, in general it is recognized that the fisher is a monotypic genus with no extant subspecies.
Read more about this topic: Fisher (animal)
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