Name Meaning:  Beaver Form (common name:  Giant Beaver)

Geologic Era:  Pleistocene

Location Found:  Florida

Size:  2.2 meters long not including tail (with tail, close to 3 meters)

Estimated Range:  Most of North America including Canada

Extinction Date:  End of Pleistocene (as late as 10,000 years ago)

Another example of the Ice Age megafauna, Castoroides certainly lived up to its nickname of “Giant Beaver.”  While modern beavers seldom exceed .7 meters in length (including tail) and 50 kilograms, Castoroides was nearly three times that length and generally reached 120 kilograms.  Castoroides has the distinction of being the largest rodent ever found on the North American continent.  The megafauna generally looked like scaled up, bulkier versions of modern animals such as ground sloths, deer, and lions.  They all disappeared at roughly the same time, around 10,000 years ago.

The incisors of Castoroides, while impressive, are not actually as well suited to gnawing wood as modern beavers.  Castoroides’ incisors were bigger and thicker than a modern beaver.  This evidence, along with reduced brain mass, suggests that Castoroides did not build dams like modern beavers, and may have been less socially adept than their modern counterparts.  Also, reconstruction is based off of modern species.  We cannot know for certain, for example, if Castoroides had webbed feet and a broad tail like modern beavers, but it can be assumed that they probably did.  What can be inferred from the skull of Castoroides is that is was well suited to longer dives underwater, which would lend credence to the idea of webbed feet and wide tails.

Castoroides was originally discovered in Ohio in 1837, but its range spread as far North as Canada and as far South as Florida.  Some possible evidence for Castoroides lodges were found, but can probably be attributed to rain washing out dead tree limbs and trunks.  However, recently a lodge made by a related species has been unearthed, which suggests that Castoroides was capable of this as well.  The only definitive proof will be of a lodge found with a Castoroides skeleton in or near it.  If that is the case, than it would make the beaver lodges of today seem insignificant.  Beaver lodges today can easily dam up streams; imagine what an animal well over twice the size could have built.    

Castoroides would have been a prey animal to creatures such as saber-toothed cats, wolves, and bears.  Taking to the water would have been its primary defense, as well as making itself inaccessible to predators.  Impressive though its incisors are, they probably would not have been effectively used for defense.

What ultimately caused the decline and extinction of the American megafauna is still something of a mystery, though it does somewhat coincide with the arrival of humans on the North American continent.  Humans are unlikely to the single cause of the extinction event, though they may have contributed.  Indeed, population decline of many megafauna species seems to somewhat predate the arrival of humans.  A more direct cause would probably have been the decline in forage quality at the time.  A decrease in forage quality would have led to decreased nitrogen in the soil, which would have further damaged forage.  This vicious cycle was probably the primary reason for the decline and extinction of the Pleistocene megafauna.  In effect, these large animals starved themselves out due to their sheer body size.  In this case, bigger wasn’t necessarily better.

Image Credits:

Skeleton:  “Giant-beaver-fieldmuseum”. Licensed under CC BY-SA 3.0 via Commons – https://commons.wikimedia.org/wiki/File:Giant-beaver-fieldmuseum.jpg#/media/File:Giant-beaver-fieldmuseum.jpg


Size Comparison:http://www.prehistoric-wildlife.com/species/c/castoroides.html


Life Restoration:”Castoroides Knight” by Charles Robert Knight – Charles R. Knight: he Artist Who Saw Through Time (scan). Licensed under Public Domain via Commons – https://commons.wikimedia.org/wiki/File:Castoroides_Knight.jpg#/media/File:Castoroides_Knight.jpg