6,000 year old mute swan subfossils have been found in post-glacial peat beds of East Anglia. Fossils have been recorded in Ireland, Portugal, Italy and France, dating back to 13,000 BP.
Fossils of swan ancestors more distantly allied to the mute swan have been found in four U.S. states: California, Arizona, Idaho and Oregon. The timeline runs from the Miocene to the late Pleistocene eras, or 10,000 BP. The latest find was in Anza Borrego Desert, a state park in California. Fossils from the Pleistocene include Cygnus paloregonus from Fossil Lake, Oregon, Froman's Ferry, Idaho, and Arizona, referred to by Howard in The Waterfowl of the World as "probably the mute type swan".