Hagerman's Fossil Beaver

Beavers are large semi-aquatic rodents that are common in wet areas throughout North America and Eurasia. Beavers are sometimes considered pests due to their industrious nature and habit of rerouting waterways — which can flood farmlands and even homes—but these “environmental engineers” serve an important function in maintaining local biodiversity (number of plant and animal species).
Beavers are a “keystone species”. Keystone species ensure the health and productivity of their local ecosystem, and their absence can have a significant negative impact. Beaver activity, like cutting down trees and building dams, opens wooded areas and encourages light-dependent plants to grow. This, in turn, attracts insects, birds, and various other animals. Beaver activity can create vital habitats for endangered species, animals hunted or fished recreationally, and colorful birds that can attract recreational visitors.

The natural world is inextricably linked! For example, the reintroduction of wolves at Yellowstone National Park led to a decline in elk. This might sound bad, but elk numbers were artificially high due to a lack of predators. The decline in elk led to an increase in willow trees which decreased erosion and lead to a greater overall variety of plants and animals. The beaver was one of the many animals to return, and its presence is further helping to increase biodiversity to the Greater Yellowstone Area. Who knew that beavers could be important!
So, why are we talking about beavers on a fossil page? Because beavers have been around, shaping their environment, for a very long time: over 30 million years!
The fossil beavers of Hagerman are not THAT old, of course, since our fossils are from the Pliocene Epoch (5.3-2.58 million years ago) and have been dated to between 4.2 and 3.0 million years in age. Our fossil beaver was actually very similar to today’s modern beaver. This is reflected in its name (Castor californicus) which shares the same genus name as today’s North American beaver (Castor canadensis). In scientific classification (naming of living things) two animals of the same genus are closer related than those of two different genera. Indeed, our beaver differs mainly in its size in that it was quite a bit bigger than beavers of today.
Many beaver fossils have been found at Hagerman, but they are more common from Hagerman’s older deposits. This reflects a changing climate. The Pliocene was actually a very dynamic time for the world’s climate. At Hagerman we see evidence for three shifts: from cool and wet to warm and wet and then to a dry and cool climate. This cooling led into the Pleistocene (2.58 million to 11,700 years ago) where glacial advance led to drops in sea levels and a markedly cooler and drier climate. The tenacious beaver adapted and persevered while many other animals went extinct.
Fur trapping of beavers over the last several centuries almost led to this furry rodent's demise, but today with greater regulations in place, the beaver is making a come-back. Let’s hope the beaver sticks around for millions of years to come!

Last updated: May 18, 2017

Contact the Park

Mailing Address:

PO Box 570
Hagerman, ID 83332


(208) 933-4105

Contact Us