The family Castoridae contains the two living species of

beaver Beavers are large, semiaquatic rodents in the genus ''Castor'' native to the temperate Northern Hemisphere. There are two extant species: the North American beaver (''Castor canadensis'') and the Eurasian beaver (''C. fiber''). Beavers a ...

s and their

fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...

relatives. A highly diverse group of

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

s within this family once roamed the earth, but only a single genus is extant today, '' Castor''.

Characteristics

Castorids are medium-sized mammals, although large compared with most other rodents. They are semiaquatic, with sleek bodies and webbed hind feet, and are more agile in the water than on land. Their tails are flattened and scaly, adaptations that help them manoeuvre in the water. Castorids live in small family groups that each occupy a specific territory, based around a lodge and dam constructed from sticks and mud. They are herbivores, feeding on leaves and grasses in the summer, and woody plants such as willow in the winter. They have powerful incisors and the typical rodent

dental formula Dentition pertains to the development of teeth and their arrangement in the mouth. In particular, it is the characteristic arrangement, kind, and number of teeth in a given species at a given age. That is, the number, type, and morpho-physiolog ...

Evolution

The earliest castorids belong to the genus '' Agnotocastor'', known from the late

Eocene The Eocene ( ) Epoch is a geological epoch that lasted from about 56 to 33.9 million years ago (mya). It is the second epoch of the Paleogene Period in the modern Cenozoic Era. The name ''Eocene'' comes from the Ancient Greek (''ēṓs'', ...

and

Oligocene The Oligocene ( ) is a geologic epoch of the Paleogene Period and extends from about 33.9 million to 23 million years before the present ( to ). As with other older geologic periods, the rock beds that define the epoch are well identified but t ...

North America North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and th ...

and

Asia Asia (, ) is one of the world's most notable geographical regions, which is either considered a continent in its own right or a subcontinent of Eurasia, which shares the continental landmass of Afro-Eurasia with Africa. Asia covers an are ...

. Other early castorids included genera such as '' Steneofiber'', from the Oligocene and

Miocene The Miocene ( ) is the first geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and means "less recen ...

of Europe, the earliest member of the subfamily Castorinae, which contains castorids closely related to living beavers. Their teeth were not well suited to gnawing wood, suggesting this habit evolved at a later point, but they do appear adapted to semiaquatic living. Later, such early species evolved into forms such as ''

Palaeocastor ''Palaeocastor'' ('prehistoric beaver') is an extinct genus of beavers that lived in the North American Badlands during the late Oligocene period to early Miocene. ''Palaeocastor'' was much smaller than modern beavers. There are several species ...

'' from the

Nebraska Nebraska () is a state in the Midwestern region of the United States. It is bordered by South Dakota to the north; Iowa to the east and Missouri to the southeast, both across the Missouri River; Kansas to the south; Colorado to the sout ...

. ''Palaeocastor'' was about the size of a muskrat, and dug corkscrew-shaped burrows up to deep. Eucastor tortus

Giant forms evolved in the

Pleistocene The Pleistocene ( , often referred to as the ''Ice age'') is the geological Epoch (geology), epoch that lasted from about 2,580,000 to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was fina ...

, including '' Trogontherium'' in Europe, and '' Castoroides'' in North America. The latter animal was as large as a black bear, yet had a brain only marginally larger than that of modern beavers. Its shape suggests it would have been a good swimmer, and it probably lived in

swamp A swamp is a forested wetland.Keddy, P.A. 2010. Wetland Ecology: Principles and Conservation (2nd edition). Cambridge University Press, Cambridge, UK. 497 p. Swamps are considered to be transition zones because both land and water play a role in ...

y habitats.

Taxonomy

McKenna and BellMcKenna, Malcolm C., and Bell, Susan K. 1997. ''Classification of Mammals Above the Species Level.'' Columbia University Press, New York, 631 pp. . divided Castoridae into two subfamilies, Castoroidinae and Castorinae. More recent studies have recognized two additional subfamilies of basal castorids, Agnotocastorinae and Palaeocastorinae, which is followed here. Within the family, Castorinae and Castoroidinae are sister taxa; they share a more recent common ancestor with each other than with members of the other two subfamilies. Both subfamilies include semiaquatic species capable of constructing dams. The Palaeocastorinae include beavers that are interpreted as

fossorial A fossorial () animal is one adapted to digging which lives primarily, but not solely, underground. Some examples are badgers, naked mole-rats, clams, meerkats, and mole salamanders, as well as many beetles, wasps, and bees. Prehistoric evid ...

(burrowing), as are nothodipoidins and ''

Migmacastor ''Migmacastor'' is an extinct member of the beaver family, Castoridae, known from a single species, ''Migmacastor procumbodens''. Only a single specimen has been reported, a skull from the late Oligocene or early Miocene of Nebraska. Features of ...

''.Korth W.W., 2007b. The skull of Nothodipoides (Castoridae, Rodentia) and the occurrence of fossorial adaptations in beavers Journal of Paleontology 81(6):1533-1537. The following taxonomy is based on KorthKorth W.W., 2007a. A new genus of beaver (Rodentia, Castoridae) from the Miocene (Clarendonian) of North America and systematics of the Castoroidinae based on comparative cranial anatomy Annals of Carnegie Museum 76(2):117-134. and Rybczynski, with preference given to the latter where these differ. *Family Castoridae **†''

'' **Subfamily † Agnotocastorinae (

paraphyletic In taxonomy, a group is paraphyletic if it consists of the group's last common ancestor and most of its descendants, excluding a few monophyletic subgroups. The group is said to be paraphyletic ''with respect to'' the excluded subgroups. In ...

) ***Tribe † Agnotocastorini ****†'' Agnotocastor'' ****†'' Neatocastor'' ***Tribe † Anchitheriomyini ****†'' Anchitheriomys'' ****†'' Propalaeocastor'' ****†'' Oligotheriomys'' **Subfamily † Palaeocastorinae ***†''

'' ***†'' Capacikala'' ***†'' Pseudopalaeocastor'' ***Tribe † Euhapsini ****†'' Euhapsis'' ****†'' Fossorcastor'' **Subfamily † Castoroidinae ***†'' Priusaulax'' (placement in Castoroidinae questionable) ***Tribe † Nothodipoidini ****†''

Eucastor ''Eucastor'' is an extinct genus of beaver-grouped rodents. Based on the available evidence of the foramina In anatomy and osteology, a foramen (;Microdipoides'' ****†'' Nothodipoides'' ***Tribe † Castoroidini (paraphyletic) ****†'' Monosaulax'' ****†'' Prodipoides'' ****†''

Dipoides ''Dipoides'' is an extinct genus (biology), genus of beaver-grouped rodents. ''Dipoides'' were about two thirds the size of modern Canadian beavers. Where modern beavers have square chisel shaped teeth, ''Dipoides'' teeth were rounded. However ...

'' ****†'' Castoroides'' ****†''

Procastoroides ''Procastoroides'' is an extinct genus of beaver-grouped rodent Rodents (from Latin , 'to gnaw') are mammals of the order Rodentia (), which are characterized by a single pair of continuously growing incisors in each of the upper and lo ...

'' ***Tribe † Trogontheriini ****†'' Trogontherium'' ****†'' Boreofiber'' ****†'' Euroxenomys'' ****†'' Youngofiber'' ****†'' Asiacastor'' **Subfamily Castorinae ***†'' Chalicomys'' (also incorrectly "''Palaeomys''") ***†'' Steneofiber'' ***†'' Zamolxifiber'' ***†'' Romanofiber'' ***†'' Schreuderia'' ***†'' Sinocastor'' ***†'' Hystricops'' ***'' Castor'' - modern beavers **** North American beaver, ''Castor canadensis'' **** Eurasian beaver, ''Castor fiber'' ****†'' Castor californicus''

References

{{Taxonbar, from=Q261363 Rodent families Beavers Extant Eocene first appearances Taxa named by Wilhelm Hemprich Semiaquatic animals