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Episode 161: Beavers are Busy

Every week we learn something new and are amazed by the species we cover. The Beaver is no exception. An incredible, industrious species, we are just blown away once again by a species many love. Beavers also are a keystone species and have an interesting conservation story.

Beaver History

About 195 Ma, Hadrocoidium wui, the potential fossil ancestor of all mammals, looked very much like a small mouse. Since, rodents evolved about 70 million year ago with lagomorphs (rabbits, hares, pikas). Today, rodents are the dominant mammalian family, with 42% of all mammals a rodent. There are about 2,277 species of rodents.

Beavers are a very unique genera of rodent. They span about 40 million years. Around this time, the branch leading to beavers diverged from the common ancestor with the scaly tailed squirrel Anomalurus. Within Beavers are two species:

These are very two distinct species. A study of beaver mitochondrial genomes showed that Castor canadensis branched off of Castor fiber about 7.5 million years ago when the animal migrated into the North American continent from Asia.

Beaver Physiology

Beavers can live up 15 to 20 years in the wild. They are a highly adapted species and are critical to riparian ecosystems. However, as discussed, they were introduced to Argentina and are now an invasive species. A good article discussing this can be read HERE

Beavers have many adaptations for their lives of cutting down trees, building dams and their lodges. For example, their orange teeth are high in iron, and evolved to be sharp and durable. Their large flat tails are used as rudders while they swim and help balance them while sitting. One interesting fact is the anal glands of Beavers, which when expressed smell like vanilla. Finally, their nose and ear valves shut to keep out water while submerged, and nictitating membranes or transparent “third eyelids” act as goggles. Perhaps most useful is that their lips close behind their oversized front teeth, allowing the beaver to transport building materials and food without drowning.


Beavers were hunted for their pelts for many centuries. They were greatly reduced in number and pushed out of many areas of their habitat. In fact, in countries like the UK, Beavers were hunted to extinction. However, Beavers have rebounded and are even being reintroduced to many areas, like the UK. Both species are listed as Least Concern by the IUCN.



May 19, 2020
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