Scientists and paleontologists cannot precisely identify the cause of the beaver's extinction. But several theories account for the extinction of many large mammals in North America, including the giant beaver. Scientists approximately date the extinction to 11,000 years ago. At the same time, extinctions also occurred in South America, Australia and, to a lesser degree, in parts of Europe, Asia and Africa. Problematically, current theories of extinction fail to account for these extinctions that occurred elsewhere around the world.
Some scientists maintain human hunting caused the extinction of mammals in North America. It is believed that migrants from Asia entered the New World around 14,000 years ago, as evidenced by artifacts and sites that have been discovered across North America. These tribal peoples are believed to have hunted and gathered wild animals and plants, some of which became extinct and some of which survive today. Some researchers suggest that the over-hunting of certain mammals around the end of the Pleistocene period directly caused the extinction. Other researchers suggest that the over-hunting eradicated a "keystone species," such as the mammoths or the mastrodens, and that this indirectly caused extinction of other species, including the beaver, by collapses in the environmental structure.
Environmental causes resulting from climate change are also cited as a cause of extinction. Experts believe that between 18,000 and 11,500 years ago, temperatures in North America warmed dramatically and rainfall patterns changed. These climate changes fundamentally changed existing ecosystems in the continent. Plants and animals were forced to relocate to new habitats. Many species simply did not survive the adjustments to a new community. The giant beaver, for instance, was forced to disperse to land, as droughts eliminated the lakes, ponds and swamps that giant beavers preferred. Unable to build dams, populations of giant beaver dwindled, and only the smaller, more adaptable, species of beavers survived.
Another theory of extinction is hyperdisease, or the rapid spread of highly infectious diseases. According to this theory, the human populations that expanded to North America during the Pleistocene carried disease-causing agents from the old world. These diseases were quickly communicated from humans or animal carriers, such as dogs, to native fauna. The diseases were so lethal, according to proponents of the theory, that they quickly eradicated many species of native animals, including the giant beaver.