''Castoroides'' (from

Latin Latin ( or ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken by the Latins (Italic tribe), Latins in Latium (now known as Lazio), the lower Tiber area aroun ...

''castor'' (beaver) and -''oides'' (like)), or the giant beaver, is an extinct genus of enormous, bear-sized

beaver Beavers (genus ''Castor'') are large, semiaquatic rodents of the Northern Hemisphere. There are two existing species: the North American beaver (''Castor canadensis'') and the Eurasian beaver (''C. fiber''). Beavers are the second-large ...

s that lived in

North America North America is a continent in the Northern Hemisphere, Northern and Western Hemisphere, Western hemispheres. North America is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South Ameri ...

during the

Pleistocene The Pleistocene ( ; referred to colloquially as the ''ice age, Ice Age'') is the geological epoch (geology), epoch that lasted from to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was fin ...

. Two species are currently recognized, ''C. dilophidus'' in the

Southeastern United States The Southeastern United States, also known as the American Southeast or simply the Southeast, is a geographical List of regions in the United States, region of the United States located in the eastern portion of the Southern United States and t ...

and ''C. ohioensis'' in most of North America. ''C. leiseyorum'' was previously described from the

Irvingtonian The Irvingtonian North American Land Mammal Age on the geologic timescale is the North American faunal stage according to the North American Land Mammal Ages chronology (NALMA), spanning from 1.8 million – 250,000 years Before Present, BP.

age but is now regarded as an invalid name. All specimens previously described as ''C. leiseyorum'' are considered to belong to ''C. dilophidus''.

Description

''Castoroides'' species were much larger than modern beavers. Their average length was approximately , and they could grow as large as . The weight of the giant beaver could vary from to . This makes it the largest known

rodent Rodents (from Latin , 'to gnaw') are mammals of the Order (biology), order Rodentia ( ), which are characterized by a single pair of continuously growing incisors in each of the upper and Mandible, lower jaws. About 40% of all mammal specie ...

in North America during the

and the largest known beaver. Recent analyses suggest that they weighed less, closer to , but this is disputable. The hind feet of the giant beaver were much larger than in modern beavers, while the hind legs were shorter. The tail was longer and may not have been paddle-shaped as in modern beavers. It can only be assumed that its feet were webbed as in modern species. The skull structure of the giant beaver suggests that it participated in extended underwater activity, thanks to the ability to take more oxygen into its lungs. Castoroides dilophidus

One of the defining characteristics of the giant beaver was their

incisor Incisors (from Latin ''incidere'', "to cut") are the front teeth present in most mammals. They are located in the premaxilla above and on the mandible below. Humans have a total of eight (two on each side, top and bottom). Opossums have 18, wher ...

teeth, which differed in size and shape from those of modern beavers. Modern beavers have incisors with smooth enamel, while the teeth of the giant beaver had a striated, textured enamel surface. Their teeth were also much larger, up to 15 cm (6 in) long.

Classification

There are two known species: *''Castoroides dilophidus'' (found in

Florida Florida ( ; ) is a U.S. state, state in the Southeastern United States, Southeastern region of the United States. It borders the Gulf of Mexico to the west, Alabama to the northwest, Georgia (U.S. state), Georgia to the north, the Atlantic ...

and the southeastern states only) *''Castoroides ohioensis'', synonym ''Castoroides nebrascensis'' (found throughout continental United States and Canada) These two species of giant beaver (genus ''Castoroides'') are not close relatives to modern beavers (genus ''Castor''), with modern beavers and ''Castoroides'' suggested to have split around 16-20 million years ago based on fossils and genomic estimates. ''Castoroides'' typifies the extinct subfamily ''Castoroidinae'', which forms a North American lineage beginning with the

Hemingfordian The Hemingfordian on the geologic timescale is the North American faunal stage according to the North American Land Mammal Ages chronology (NALMA), typically set from 20,600,000 to 16,300,000 years BP. It is usually considered to overlap the lates ...

genus '' Monosaulax'', followed by '' Eucastor'', '' Dipoides'', and '' Procastoroides'', to finally culminate and go extinct with ''Castoroides''. Castoroides Knight

Discovery and species

''Castoroides'' fossils were first discovered in 1837 in a peat bog in

Ohio Ohio ( ) is a U.S. state, state in the Midwestern United States, Midwestern region of the United States. It borders Lake Erie to the north, Pennsylvania to the east, West Virginia to the southeast, Kentucky to the southwest, Indiana to the ...

, hence the species epithet ''ohioensis''. ''Castoroides'' had cutting teeth up to 15 cm-long with prominently-ridged outer surfaces. These strong enamel ridges would have acted as girders to support such long teeth. Further, the deep masseteric fossa of the lower jaw suggests a very powerful bite. Remains of the giant beaver, along with Paleo-Indian artifacts and the remains of the flat-headed peccary, giant short-faced bear, and the stag moose were found in the Sheriden Cave in Wyandot County, Ohio. Fossils of ''Castoroides'' are concentrated around the

midwestern United States The Midwestern United States (also referred to as the Midwest, the Heartland or the American Midwest) is one of the four census regions defined by the United States Census Bureau. It occupies the northern central part of the United States. It ...

in states near the

Great Lakes The Great Lakes, also called the Great Lakes of North America, are a series of large interconnected freshwater lakes spanning the Canada–United States border. The five lakes are Lake Superior, Superior, Lake Michigan, Michigan, Lake Huron, H ...

, particularly

Illinois Illinois ( ) is a U.S. state, state in the Midwestern United States, Midwestern United States. It borders on Lake Michigan to its northeast, the Mississippi River to its west, and the Wabash River, Wabash and Ohio River, Ohio rivers to its ...

and

Indiana Indiana ( ) is a U.S. state, state in the Midwestern United States, Midwestern region of the United States. It borders Lake Michigan to the northwest, Michigan to the north and northeast, Ohio to the east, the Ohio River and Kentucky to the s ...

, but specimens are recorded from

Alaska Alaska ( ) is a non-contiguous U.S. state on the northwest extremity of North America. Part of the Western United States region, it is one of the two non-contiguous U.S. states, alongside Hawaii. Alaska is also considered to be the north ...

and Canada to

. In Canada, fossils of this species are commonly found in the Old Crow Basin, Yukon, and single specimens are known from Toronto, Ontario and Indian Island, New Brunswick. A hitherto overlooked 1891 record of a ''Castoroides'' skull from near Highgate, Ontario is the earliest for Canada. In Old Crow region, ''Castoroides'' fossils occur in deposits of the

Sangamonian The Sangamonian Stage (or Sangamon interglacial) is the term used in North America to designate the Last Interglacial (130,000-115,000 years ago) and depending on definition, part of the early Last Glacial Period, corresponding to Marine Isotope St ...

interglacial. The discovery of giant beaver remains in New Brunswick adds significantly to the

Quaternary The Quaternary ( ) is the current and most recent of the three periods of the Cenozoic Era in the geologic time scale of the International Commission on Stratigraphy (ICS), as well as the current and most recent of the twelve periods of the ...

terrestrial mammal fauna of New Brunswick and suggests that the terrestrial fauna was probably richer than earlier evidence indicated. The known North American distribution of giant beaver is not significantly changed by this occurrence. Specimens from the southeastern U.S. have been placed in a separate species, ''Castoroides dilophidus'', based on differences in

premolar The premolars, also called premolar Tooth (human), teeth, or bicuspids, are transitional teeth located between the Canine tooth, canine and Molar (tooth), molar teeth. In humans, there are two premolars per dental terminology#Quadrant, quadrant in ...

and molar features. Martin (1969) considered it a subspecies, but new research by Hulbert et al. place them in their own species, ''Castoroides dilophidus'', It is recorded from more than 25 Pleistocene localities in Florida, 23 of Rancholabrean age, one possibly of

age, and one of late

Blancan The Blancan North American Stage on the geologic timescale is the North American faunal stage according to the North American Land Mammal Ages chronology (NALMA), typically set from 4,750,000 to 1,806,000 years BP, a period of . ''Castoroides dilophidus'' specimens have been unearthed in Florida and South Carolina. The Cooper River site in South Carolina was dated at 1.8 million to 11,000 years ago. The ''Castoroides leiseyorum'' was named by S. Morgan and J. A. White in 1995 for the Leisey shell pit in

Hillsborough County, Florida Hillsborough County is located in the west-central portion of the U.S. state of Florida. In the 2020 census, the population was 1,459,762, making it the fourth-most populous county in Florida and the most populous county outside the Miami metro ...

, with specimens aged at about 2.1 Mya. These specimens are now considered to belong to ''C. dilophidus'', and ''C. leiseyorum'' is no longer a valid species name.

Ecology

Stable isotopes suggest that ''Castoroides'' probably predominantly consumed submerged aquatic plants, rather than the woody diet of living beavers. There is no evidence that giant beavers constructed dams or lodges. The shape of the incisors of ''Castoroides'' would have made it much less effective in cutting down trees than living beavers. It was likely heavily dependent on wetland environments for both food and protection from predators.

Extinction

''Castoroides'' was likely extirpated from Alaska and the Yukon after 75,000 years ago corresponding to increasingly hostile environmental conditions. ''Castoroides'' went extinct during as part of the

Late Pleistocene extinctions The Late Pleistocene to the beginning of the Holocene saw the extinction of the majority of the world's megafauna, typically defined as animal species having body masses over , which resulted in a collapse in faunal density and diversity acro ...

at the Pleistocene–

Holocene The Holocene () is the current geologic time scale, geological epoch, beginning approximately 11,700 years ago. It follows the Last Glacial Period, which concluded with the Holocene glacial retreat. The Holocene and the preceding Pleistocene to ...

transition, alongside most other North American Pleistocene

megafauna In zoology, megafauna (from Ancient Greek, Greek μέγας ''megas'' "large" and Neo-Latin ''fauna'' "animal life") are large animals. The precise definition of the term varies widely, though a common threshold is approximately , this lower en ...

, such as

mammoth A mammoth is any species of the extinct elephantid genus ''Mammuthus.'' They lived from the late Miocene epoch (from around 6.2 million years ago) into the Holocene until about 4,000 years ago, with mammoth species at various times inhabi ...

s and

mastodon A mastodon, from Ancient Greek μαστός (''mastós''), meaning "breast", and ὀδούς (''odoús'') "tooth", is a member of the genus ''Mammut'' (German for 'mammoth'), which was endemic to North America and lived from the late Miocene to ...

s. This roughly coincides with the arrival of the

Clovis culture The Clovis culture is an archaeological culture from the Paleoindian period of North America, spanning around 13,050 to 12,750 years Before Present (BP). The type site is Blackwater Draw locality No. 1 near Clovis, New Mexico, where stone too ...

in the region—who rapidly colonized the area by 12,800 years ago—as well the beginning of an aridity trend. It has been long debated if humans (" overkill hypothesis") or climate change had a bigger effect in the extinction event, but they took several thousands of years to completely die out. The loss of both wetland habitats in lowland regions and associated mixed-conifer forests coincide with regional disappearances of ''Castoroides'' populations in North America. ''Castoroides'' populations were extirpated from different regions such as the southeast,

Great Plains The Great Plains is a broad expanse of plain, flatland in North America. The region stretches east of the Rocky Mountains, much of it covered in prairie, steppe, and grassland. They are the western part of the Interior Plains, which include th ...

regions, and northern North America (Canada and Alaska) as a direct result of local glacial periods within the

Last Glacial Maximum The Last Glacial Maximum (LGM), also referred to as the Last Glacial Coldest Period, was the most recent time during the Last Glacial Period where ice sheets were at their greatest extent between 26,000 and 20,000 years ago. Ice sheets covered m ...

that brought aridification to the habitats and made them unsuitable. Radiocarbon dates from Ohio and New York indicate that the lowlands south of the Great Lakes was home to the last isolated ''Castoroides'' populations when it disappeared from eastern North America shortly before the Pleistocene-Holocene transition event, bringing the complete extinction of the genus. The youngest known ''Castoroides'' specimens from New York State overlap with human artifacts (dating to 10,150 ± 50 years BP uncalibrated, later estimated to range from 11,501 to 12,050 years BP in calibrated radiocarbon date), suggesting that it overlapped with Paleo-Indian populations for up to a thousand years. However, there is no zooarchaeological evidence that humans butchered, hunted, or used ''Castoroides'' as a resource. Although causes of extinction of the Great Lakes Basin population are not specifically known, potential competition for habitat space and

climate change Present-day climate change includes both global warming—the ongoing increase in Global surface temperature, global average temperature—and its wider effects on Earth's climate system. Climate variability and change, Climate change in ...

brought about their extinction.

Interaction with humans

Little is known for certain about human interactions with ''Castoroides''. Remains of ''Castoroides'' are found along with human artefacts in Sheriden Cave. Differing scientific theories exist considering whether the extinction of ''Castoroides'' was caused by hunting by the early human arrivals in the Americas.

First Nations First nations are indigenous settlers or bands. First Nations, first nations, or first peoples may also refer to: Indigenous groups *List of Indigenous peoples *First Nations in Canada, Indigenous peoples of Canada who are neither Inuit nor Mé ...

such as the

Innu The Innu/Ilnu ('man, person'), formerly called Montagnais (French for ' mountain people'; ), are the Indigenous Canadians who inhabit northeastern Labrador in present-day Newfoundland and Labrador and some portions of Quebec. They refer to ...

and

Mississaugas The Mississaugas are a group of First Nations peoples located in southern Ontario, Canada. They are a sub-group of the Ojibwe Nation. Etymology The name "Mississauga" comes from the Anishinaabe word ''Misi-zaagiing'', meaning " hose at theGr ...

feature giant beaver in their traditional mythology, which some members of these Nations believe is evidence of human interaction with ''Castoroides''. In 1972, American ethnologist Jane Beck hypothesized ''C. ohioensis'' was the basis of an Algonquin myth where a gargantuan beaver created a dam so high on the Saint John River, the lake behind it almost reached the sea. The dam was struck down by the Wabanaki heroic figure Glooscap with his axe, creating the Reversing Falls. Glooscap chased the monster upstream, creating several islands in the river while attempting to strike the beaver through the ice. The beaver constructed another dam which created the Great Lakes and fled through these to the land beyond. Several versions of an

Anishinaabe The Anishinaabe (alternatively spelled Anishinabe, Anicinape, Nishnaabe, Neshnabé, Anishinaabeg, Anishinabek, Aanishnaabe) are a group of culturally related Indigenous peoples of the Americas, Indigenous peoples in the Great Lakes region of C ...

story tell of "giant beavers" who "walked upright and stood as tall as the tallest man." Many scholars believe that stories like these could be evidence from the

oral tradition Oral tradition, or oral lore, is a form of human communication in which knowledge, art, ideas and culture are received, preserved, and transmitted orally from one generation to another.Jan Vansina, Vansina, Jan: ''Oral Tradition as History'' (19 ...

of North American First Nations people encountering ''C. ohioensis'' or, at the very least, their fossils.Ethnohistory. No. 2, (Spring, 1972) ed., Vol. 19, Duke University Press, 1999.

References

*Ruez, Dennis R, "Early Irvingtonian (Latest Pliocene) Rodents from Inglis 1C, Citrus County, Florida", 2001 The Society of Vertebrate Paleontology. *Alroy, J., Equilibrial diversity dynamics in North American mammals. pp. 232–287 in M. L. McKinney and J. A. Drake (eds.), Biodiversity dynamics: turnover of populations, taxa, and communities. Columbia University Press, New York. *Swinehart, Anthony L., and Richards, Ronald L. "Palaeoecology of a Northeast Indiana Wetland Harboring Remains of the Pleistocene Giant Beaver (''Castoroides Ohioensis'')." Indiana Academy of Science, 2001. {{Taxonbar, from=Q1866419 Pliocene rodents Pleistocene rodents Piacenzian first appearances Pleistocene genus extinctions Prehistoric beavers Prehistoric rodent genera Pliocene mammals of North America Pleistocene mammals of North America Taxa named by John Wells Foster Fossil taxa described in 1838 Species that are or were threatened by climate change Species that are or were threatened by human consumption