An Ultimate Guide to Castoroides: The Beaver-Like

Leave a comment / / Updated on: 24th September 2023

Name Meaning“Beaver Like”Height1.9 meters (6.2 ft.)
PronunciationCas-tor-oy-deesLength2.5 meters (7.5 ft.)
EraCenozoic– Quaternary PeriodWeight90 to 125 kgs (198 to 276 lbs.)
ClassificationMammalia, Rodentia,‭ ‬CastoridaeLocationNorth America

Castoroides Beaver Pictures

Castoroides | Hammerbro123 via Dinopedia Fandom

The Castoroides

Gage Beasley Prehistoric's Castoroides Concept
Gage Beasley Prehistoric’s Castoroides Concept

Beavers are one of the most iconic animals in North America, and today there are around 24 subspecies that are a part of the two existing species.

Around 10,000 years ago, before going extinct, Castoroides, the Giant Beaver, inhabited North America for more than a million years and were much larger than the smaller beavers we see today.

The first fossil specimens of Castoroides were discovered in 1837 in Ohio, and there are two known species.

Megafauna like Castoroides were abundant around the globe, and these giants resemble a plethora of animals that we see today.

Gage Beasley's Prehistoric Shirt Collection
Gage Beasley’s Prehistoric Shirt Collection
Gage Beasley's Prehistoric Plush Collection
Gage Beasley’s Prehistoric Plush Collection

Giant sloths, short-faced bears, the American lion, and the mammoths are just some of the megafauna that lived in North America before going extinct, but this article will go over the amazing things about Castoroides, the giant beaver.

Fossils from Castoroides have been mainly seen around the midwestern United States, and evidence suggests they inhabited the great lakes.

Here we will take a look at Castoroides and cover things like their habitat, range, diet, and how these giant beavers fit into the Pleistocene environment.

Physical Characteristics

Gage Beasley Prehistoric's Castoroides Size Comparison Chart
Gage Beasley Prehistoric’s Castoroides Size Comparison Chart

Compared to the modern beaver species alive today, Castoroides was much larger and heavier but probably had a similar appearance to their distant relatives. 

Castoroides had an average length of around 1.9 meters (6.2 ft.), but could grow up to 2.2 meters (7.2 ft.) in length. 

Castoroides had a weight estimated between 90 to 125 kgs. (198 to 276 lbs).

There have been several studies estimating these beavers’ weight, and more recent studies suggest they could have been smaller, weighing around 77 kgs. (170 lbs), but some scientists consider this to be inaccurate. 

Along with being much larger in size than the modern beaver, Castoroides had huge curved teeth that measured up to 15 cm (6 in.) in length.

Castoroides’ size is not the only difference they had with modern beavers, but they had a long tail that is not thought to have a paddle shape and a small brain when compared with its size.

Giant beavers had webbed feet, and their skull design and large lungs suggested they spent a lot of their time underwater.

At the time of its existence, Castoroides was the largest rodent to live in North America and are around 3.5 times heavier and two times larger than the biggest beaver species today. 

Habitat and Distribution

Castoroides lived in the Pleistocene period, around 2.5 million to 11,700 years ago, primarily in North America. 

Fossils from this species have been most abundant in the midwestern United States near the Great Lakes, but fossils have been seen as far south as Florida and as far north as Canada.

In Canada, these beaver fossils have been found in places like the Old Crow Basin, Yukon, Toronto, Ontario, and New Brunswick. 

There are two species currently recognized of Castoroides, which are C. dilophidus, and C. ohioensis, and their ranges are slightly different. 

Castoroieds dilophidus lived in Florida, and the southeastern United States, while C. ohioensis lived in the continental United States and Canada. 

C. leiseyorum is a species that was once listed but now is not valid and is a synonym for C. dilophidus

Wetland environments are where Castoroides lived, and they were semi-aquatic. 

There has been no evidence that the giant beaver built dams, like modern beaver species, as they did not have teeth designed as well to be constantly chopping trees. 

Giant beavers have not been found outside of North America, and their fossils suggest their main populations were near large wetlands and other water sources. 

Behavior and Diet

Castoroides looking for food in the river
Castoroides looking for food in the river | Animalman57 via DinopediaFandom

While both animals are herbivores, modern beavers feed on bark, and isotopes from Castoroides suggest they likely fed on more aquatic plants that were submerged in water. 

The diet of the giant beaver made them extremely reliant on their aquatic environment, and they likely did not stray far from the water that contained their food source. 

Evidence of the giant beaver teeth suggests they did not constantly chew wood like modern beavers, and their incisor teeth had a striated textured enamel instead of the smooth enamel that modern beavers had.

The brain size of the giant beaver also suggested they had different behaviors from modern beavers, giving them less complex patterns of behavior and thought. 

Modern beavers had the capability to stay underwater for up to 15 minutes, and the larger lungs of Castoroides helped them stay even longer underwater to feed and hide from predators. 

Plants like grasses, water lilies, cattails, and watercress are plants Castoroides could have eaten.

Due to the lack of physical defenses beavers had from predators, the water was extremely important in housing, feeding, and defending Castoroides

Life Cycle

Castoroides artist restoration
Castoroides artist restoration | Charles R. Knight via Wikipedia Public Domain

Castoroides lived in North America from around 1.9 million to 11,000 years ago before going extinct.

The giant beaver likely moved from Alaska and Yukon around 75,000 years ago since the environment began to become more hostile.

These giant beavers went extinct with the other giant megafauna that lived in North America during the Pleistocene-Holocene Transition.

The warming of the climate and competition with similar species are some of the factors that caused the giant beaver to go extinct.

There is still much mystery about the giant beaver despite them only going extinct around 11,000 years ago.

The lifespan of the giant beaver was likely similar to other members within the Castoroidae family, and they could have lived up to 20 years. 

Beavers breed by giving birth to live young, mating in the late winter, and having around a litter of multiple young a year.

Looking at species of beaver that are alive today can help us learn more about the life cycle of the extinct giant beaver, but their fossils are also important in learning how these animals are unique.

Evolution and History

Skeleton in Minnesota Science Museum
Castoroides skeleton in Minnesota Science Museum | Ryan Somma via Wikipedia CC BY 2.0

The first fossils of Castoroides were found in 1837 in a peat bog in Ohio, giving them their type species name ohioensis.

There have been several fossils from Castoroides found in North America, most of them being abundant near the Great Lakes. 

Modern beavers are the closest living ancestor to the giant beaver that are alive today.

Fossils from beavers suggest these two beavers shared a common ancestor around 24 million years ago before begging to diverge. 

The larger size and lower brain capacity that Castoroides had likely contributed to them going extinct, as the modern beaver was better equipped to survive the changing environment. 

During the end of the Pleistocene, after the last ice age, most of the giant mammals in North America died off, including Castoroides, and only the fossils and ancestors are what remain.

Interactions with Other Species

Castoroides swimming in the river
Castoroides swimming in the river | Julio Lacierda via Tumblr

Giant beavers were not the only large-sized animal alive in their time period, and fossil evidence shows the Pleistocene period had a variety of other megafauna that used their large size to survive the ice age.

Some of the animals that Castoroides lived with include animals like 

  • Ground Sloths
  • Mastodons

While being extremely large could be seen as a benefit, the giant beaver lived alongside giant predators that could have easily overpowered them.

Being so large giant beavers were a valuable food source for animals like large cats, wolves, and bears. 

The safety of the water is how the giant beaver survived alongside large and dangerous predators.

The shape and size of the giant beaver’s teeth also suggest they had a strong bite force which could have been useful in defending themselves.

Castoroides played a role in their environment similar to other large rodents like Capybaras.

Similar to other rodents and mammals, Castoroides were probably very social and lived together with one another to increase their chances of survival. 

Cultural Significance

Castoroides from ARK: Survival Evolved | Image via Dododex

The giant beaver is an important animal in learning about species that lived during the last great ice age and how animals evolve to adapt to their environment. 

Giant beavers are one of the many megafaunas that lived in North America during the Pleistocene period and helped scientists understand the type of life lived around 1 million to 10,000 years ago. 

Castoroides has also been a helpful animal in learning about the evolution of rodents over time and what caused certain species to become more successful. 

Giant animals are always some of the most interesting, and the giant beaver has been showcased in museums and video games like ARK. 

The size of Castoroides is why many people love them, but it is also intriguing how these animals survived at a time with other giant species. 


Castoroides are one of the many types of megafauna that lived in North America during the Pleistocene period.

While giant beavers are not closely related to the modern beaver, the beavers we see today and other rodents have been essential in learning about the extinct rodents of the past.

Giant beavers are around 3.5 times larger than modern beavers, and their larger size is due to the cold climate in North America and extreme size of predators at the time.

Fossils from the giant beaver have been found across North America, but near the great lakes is where they have been found the most. 

It was not only in North America did megafauna exist, but giant animals resembling the smaller species alive today could be found around the world in every continent and country. 

There are still many questions waiting to be answered about Castoroides, but the fossil evidence they left behind has been essential in uncovering the mysteries of the giant beaver. 

Giant beavers are some of the largest rodents to ever exist and evolved from the same ancestors as modern beavers around 25 million years ago. 

Megafauna may have gone extinct long ago, but their existence showcases how evolution can change animals over time to fit in their specific environments.


Did Castoroides live alongside humans?

Humans are believed to have come to North America around 15,000 to 20,000 years ago, which gives them a few thousand years where they lived alongside Castoroides.

Evidence suggesting humans interacted with giant beavers includes folklore from the past and fossils and human artifacts that date to the same period. 

There is still some confusion between Castoroides and humans, as there have been no artifacts discovered suggesting humans hunted or used the giant beaver as a resource like other giant animals.

Is Castoroides the largest rodent to ever exist?

The giant beaver Castoroides is the largest beaver known to ever exist on earth, but not the largest rodent ever, as that title goes to Josephoartigasi.

Josephoartigasia is an extinct genus that lived in Uruguay from the Early Pliocene to Early Pleistocene periods around 2 to 3 million years ago, and estimates have their weight between 400 to 700 kgs. (880 to 1,540 lbs).

Did the giant beaver live with the modern beaver?

Modern beavers’ first appearance in the fossil record dates to around 10 to 12 million years ago in Germany, and in North America, the oldest fossils of beavers were discovered in Oregon, dating to around 7 million years old.

The giant beaver and modern beavers co-existed with each other for millions of years, but only the smaller modern beavers we see today managed to survive. 

The smaller size and ability to build dams and control a dry environment are reasons that helped the modern beaver survive compared to its smaller relative.


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