Beaver Fact of the Week: The Oldest Dam Fossil

Beavers have been around a long time – building dams, swimming in their ponds – generally living the beaver dream. Exactly how long ago do we have proof of them building dams and chewed down trees?

The oldest intact fossilized beaver dam was found in Canada and is dated as approximately 125,000 years old. That must have been one sturdy dam to stay intact for so long! What’s really cool is similar to how modern beavers pack river rocks the size of soccer balls into their dams for added weight and stability, the foot bones of a woolly mammoth were found packed into the fossil dam.

The white square-ish thing in the middle of this picture is a mammoth foot bone packed into the fossilized dam, very similar to how modern beavers pack stones into their dams.

Near that fossilized dam, fossilized sticks with characteristic beaver teeth chew marks on them were also found – some of which dated 4-5 million years old! So beavers have been chewing wood, and probably building dams for at least 5 million years, and some of their dams are so solidly constructed that they stay intact for over a hundred thousand years!


4 thoughts on “Beaver Fact of the Week: The Oldest Dam Fossil

    1. The most reliable way is through carbon dating or using other geochemical dating techniques. Not easy or cheap! Other than that you can try to estimate its age by how deep it is buried and what state the wood is in.


      1. The Beaver dam in question is completely exposed and looks like solid rock. It is located in south east Idaho. I will try to get someone interested at Idaho State University and see if that might get me some answers. If you are interested, I would send you some photos if you have a way for me to send them to you. This can also be seen from google earth.


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