NPS
Skeleton of Scapanus hagermanensis.
While modern moles are limited in their distribution in Idaho today, in the past they were more widespread. The earliest fossil mole in the state is from Power County. This record is late Miocene or about 8 million years old. This early mole is the same genus, Scapanus, as the living species. Bones of a fossil mole have also been found at Hagerman. It is also the genus Scapanus, but was described as a new species, S. hagermanensis.
One would expect that a burrowing animal like a mole should be common as a fossil since it would be already "buried" and have a better chance of being preserved. But, like its modern relative it is not common and fewer than a dozen bones have been found in the Monument. The youngest fossil mole in the state is also from the Glenns Ferry Formation at Castle Butte in Owyhee County. This specimen is about 2.5 million years old, about a million years younger than the Hagerman specimens. After that there are no records until the living species.
Based on features of the teeth and skeleton, the Hagerman mole is related to the Coast mole and to Townsend's mole, Scapanus townsendi. Like the Coast mole, Townsend's mole prefers moister habitats and today lives to the west of the Cascade Mountains in Oregon and north into Canada. While we can't say for sure, it is not unreasonable to assume that like its modern relatives, the Hagerman mole preferred a moister environment. Studies of the pollen preserved at Hagerman Fossil Beds National Monument show that 3.5 million years ago, the types of plants that were here needed more moisture than the area gets today.
It has been calculated that twice as much rainfall fell in the area then, making it a much wetter, moister environment. Many of the animals found as fossils at Hagerman, such as beaver, muskrat, otter, and waterfowl, are species commonly found in a wetland habitat. Today, the Cascade Mountains to the west trap much of the moisture from the Pacific creating a rain shadow inland.
One of the possible reasons for the wetter environment in Idaho 3.5 million years ago is that the Cascades were not as tall and were not as effective in stopping moisture from the Pacific Ocean from reaching inland to Idaho. As the Cascades pushed upward they became a more effective barrier, resulting in an increasingly more arid environment in southern Idaho. As the environment became drier the different species of animals had to either adapt to the changing conditions, migrate, or go extinct. If the Hagerman mole is the ancestor to either the Coast mole or Townsend's mole then what we may be seeing in the fossil record is simply a reduction in the animal's range in response to this increasing aridity. The moles in Washington County may merely be relicts of a group that at one time was more widely distributed in Idaho.
