Equus Lambei - also known as the Yukon Horse. © Yukon Beringia Interpretive Centre
They argue that the status of wild horses in North America is important, as the approach to their management might change if they were accepted as native wildlife.
Jay Kirkpatrick, who is director of the Science and Conservation Centre in Billings, Montana, and Patricia Fazio, a research fellow at the centre, recently revised their paper, entitled "Wild Horses as Native North American Wildlife".
They said evidence dismisses the suggestion that Spanish horses (Equus caballus), introduced to the Americas in the 1500s, were of a different species to the last known horse in North America, Equus Lambei, to die out.
"The relatively new (30-year-old) field of molecular biology, using mitochondrial-DNA analysis, has recently revealed that the modern or caballine horse, E. caballus, is genetically equivalent to E. lambei, a horse, according to fossil records, that represented the most recent Equus species in North America prior to extinction," they wrote.
"Not only is E. caballus genetically equivalent to E. lambei, but no evidence exists for the origin of E. caballus anywhere except North America.
"The fact that horses were domesticated before they were reintroduced matters little from a biological viewpoint. They are the same species that originated here, and whether or not they were domesticated is quite irrelevant."
They continued: "The issue of feralisation and the use of the word 'feral' is a human construct that has little biological meaning except in transitory behaviour, usually forced on the animal in some manner."