Ancient Giant Beaver

North American Beaver>.. ................................................... Modern Urban Beaver>

Ancient Giant Beaver fossil (courtesy of source:

Scientific classification
C. leiseyorum
Binomial name
Castoroides leiseyorum

The Ancient Giant Beaver, (Castoroides leiseyorum) was a giant ancestor of the North American Beaver, that is apart of the rodent family that lived over ~2.5 million years ago. This Beaver was incredibly large, about 2.5 meters in length, and an estimated weight of between 60 to 100 kilograms. Little information is still known of the Ancient Giant Beaver, but fossils recently surfaced have given a basic understanding of the Ancient Giant Beaver. One fact known is that the fossils have only been found in North America, meaning that the North American Beaver is a direct descendant of the Ancient Giant Beaver.

Artists Sketch of Ancient Giant Beaver


It was found from carbon dating of Giant Beaver Fossils that the Giant Beaver was in existence around 2 million years ago. These fossils were found throughout areas of North America, immediately linking the large rodent with the North American Beaver. The shape of the creature does suggest that it is a good swimmer like the North American Beaver, and would have lived in many different terrains, including swampy habitats, open water, and on banks. The areas in which Fossils were found in are very hot and humid. This weather does not suit any form of Beaver and could be a contributing factor to its extinction. It is unknown wheather the Ancient Giant Beaver was a omnivore, herbivore, or carnivore, but suggested by its large, sharp teeth, it could be stated that the Giant Beaver was a carnivore or omnivore.

There were two sites where fossils were found, one in Florida, and another in South Carolina. In Florida, fossils were found in 'Leisey Shell Pit 1A and 3B' in Hillsborough County, Florida paleontological sites. A skull was found in this site, and was the first ever piece of evidence to support the question wheather a North American Beaver has a direct ancestor, or has developed from a rat. This location is very humid, but it is unsure weather it would have been like this years ago when the Ancient Giant Beaver existed, because of interference with the ice age. Carbon dating suggests that this skull is around 2.1 million years of age, the oldest found so far.

Hillsborough County, Florida

The next site in which a fossil was found is in Charleston County, South Carolina, at the Strawberry Hill site. Much like Florida, South Carolina had very humid temperatures, and very wet and marsh like habitats that would have suited the Ancient Giant Beaver due to its fondness for water. There is also a lot of rain in South Carolina, many hurricanes, and approximative 67 days of thunderous activity per year, making the weather very volatile. The fossil that was surfaced at this site was carbon dated and found to be around 1.8 million years old.

Charleston County, South Carolina

The North American Beaver was given its taxonomy name in 1995 by Morgan and White for the Leisey family who owned the quarry in which the first fossils were found. Both of these areas where fossils were found do get very warm and humid, not conditions suited to a thick furred creature. This suggests that the the ice age had made these areas much colder, and possibly turned once dry and humid habitats into swamps and marshes that are suitable for the Beaver. but for hundreds and thousands of years the Ancient Giant Beaver lived in swamps and marshes and even open water, both on land and in water. This way of living was passed onto its descendant the North American Beaver.

Swamp Lands (source:
Swamp Lands (source:

Marsh Lands (source:
Marsh Lands (source:


Structural 1

The Ancient Giant Beaver is an incredibly large rodent, and the largest ever discovered in the world. Its size is comparable to a grizzly bear. The Ancient Giant Beavers size would allow it to protect itself from prehistoric predators including the ancestors of crocodile, Leopard, Tiger and coyotes. Against these predators the Ancient Giant Beaver would have a very good chance of protecting itself and warding off these animals. This adaptation could have evolved from its earlier ancestors as possible dinosaurs which were defiantly in a size category of its own. There is also the fact of other larger predators that roamed North America before the Ancient Giant Beaver did, and it did need to protect itself, so to do this, it evolved into a large, defensive rodent. Although this is not proven and is nearly impossible to prove, it is one of the most likely reasons for the adaption of its size.

Structural 2

The second Structural adaptation the Ancient Giant Beaver had gained are its very large, and piercing teeth. Their two front teeth are extremely solid, heavy and strong. These teeth would have helped the Ancient giant Beaver pierce through meat, possibly indicating that the Ancient Giant Beaver was either an omnivore or a carnivore. There is no information to indicate that the Ancient Giant Beaver did include under tree bark as a source of energy, and some studies on fossils reveal no trace of wood from trees. This adaptation would have occurred just like any other omnivore or carnivore, the need to effectively hunt, chew and consume its food. These two teeth are perfectly suited to rip through large amounts of meat. Although this is not yet proven, this is the most likely reason for the Ancient Giant Beaver. Although this is very possible, a recent further study into the composition of carbon-12 in a Ancient Giant Beavers teeth suggested that it did have a diet that consisted of underwater plant life, possibly being the natural force that turned the Ancient Giant Beaver into the confident water dweller, the North American Beaver

Behavioral 1

The Ancient Giant Beaver would have possibly had a very violent temper. The weight of the Ancient Giant Beaver is between 60 and 100kg meaning that it would be slow, and need a way of scaring off other predators. This temper would keep the Ancient Giant Beaver safe and keep predators away, but would also help a lot when hunting. If a creature is angry and violent, whilst motivated, it could quickly end efficiently take its prey, to ensure that the Beaver stays alive, because as like all creatures, would require a constant flow of energy. This adaptation developed because surviving in these prehistoric times would be difficult and hard for all animals. Survival of the fittest takes place in times like these, and if an animal didn't have the temper to defend itself it would be its predators next meal. Therefore It gained its temper to help it hunt and survive.

Behavioral 2

Another Behavioral adaptation of the Ancient Giant Beaver is that when it does require movement on land it would do it during the night. This means that the Ancient Giant Beaver are very active at night. It would stay on land during night times to keep safe. Although the Scaring temper and size of the Ancient Beaver is a deterant for most predators, it still prefers to wonder the land at night to keep out of trouble as much as possible. The environmental pressure that would have led to this is simply survival of the fittest. The Ancient Giant Beaver tries to keep itself from predators, because their violent temper, and large size would not ward off all predators.

Side view of Ancient Giant Beaver (source:


A physiological adaptation of the Ancient Giant Beaver is its warm blood. This adaptation was carried on into the North American Beaver. The Ancient Giant Beaver needed this warm blood to survive through an ice age. Many Beaver died during the ice age, and only a few subspecies made it through. The warm blood of the Ancient Giant Beaver would have enabled it to try and adapt to the extreme cold caused by the ice age. No real environmental pressures would have caused the Ancient Giant Beaver to be warm blooded, but it was tested by the environment, and enabled the Ancient Giant Beaver to adjust to the extreme cold.

Extinction Pressure

There are many theories on what phased out the Ancient Giant Beaver. Many Giant Beavers were killed during the ice age, and many sub species became extinct. For the ones that did not however, they were brought into a land that had dried up becoming swampy forests and marshes. Once The Ancient Giant Beaver had settled into its new habitat, new creatures that have emerged from the ice age would wipe out majority of the Ancient Giant Beavers, this also includes Humans. Ecological restructuring would have also impacted heavily on the Ancient Giant Beaver, eventually extincting it. The ice age would have killed out many sub species of Giant Beaver simply from the harsh weather, and many animals also would have needed to use the Ancient Giant Beaver as a food source to survive, including humans. Once The Ancient Giant Beaver was extinct, other subspecies emerged, eventually becoming the North American Beaver.


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