Castoroidinae
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The family Castoridae contains the two living species of beavers 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 In biology, semiaquatic can refer to various types of animals that spend part of their time in water, or plants that naturally grow partially submerged in water. Examples are given below. Semiaquatic animals Semi aquatic animals include: * Ve ...
, 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 A dam is a barrier that stops or restricts the flow of surface water or underground streams. Reservoirs created by dams not only suppress floods but also provide water for activities such as irrigation, human consumption, industrial use ...
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
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 ...
s 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 of North America 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 epoch (geology), 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 mea ...
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'' from the
Miocene The Miocene ( ) is the first epoch (geology), 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 mea ...
of
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 A corkscrew is a tool for drawing corks from wine bottles and other household bottles that may be sealed with corks. In its traditional form, a corkscrew simply consists of a pointed metallic helix (often called the "worm") attached to a hand ...
-shaped burrows up to deep. Giant forms evolved in the
Pleistocene The Pleistocene ( , often referred to as the ''Ice age'') is the geological 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 finally confirmed in ...
, including ''
Trogontherium ''Trogontherium'' is an extinct genus of giant beavers, ranging from the Late Pliocene to the Late Pleistocene. It is not closely related to the North American giant beavers of the genus ''Castoroides''. Fossils of ''Trogontherium'' have been fou ...
'' in Europe, and ''
Castoroides ''Castoroides'' (Latin: "beaver" (castor), "like" (oides)), or giant beaver, is an extinct genus of enormous, bear-sized beavers that lived in North America during the Pleistocene. Two species are currently recognized, ''C. dilophidus'' in the S ...
'' in North America. The latter animal was as large as a
black bear Black bear or Blackbear may refer to: Animals * American black bear (''Ursus americanus''), a North American bear species * Asian black bear (''Ursus thibetanus''), an Asian bear species Music * Black Bear (band), a Canadian First Nations group ...
, 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 swampy 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 (burrowing), as are nothodipoidins and '' Migmacastor''.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 **†'' Migmacastor'' **Subfamily † Agnotocastorinae ( paraphyletic) ***Tribe † Agnotocastorini ****†'' Agnotocastor'' ****†'' Neatocastor'' ***Tribe † Anchitheriomyini ****†'' Anchitheriomys'' ****†'' Propalaeocastor'' ****†'' Oligotheriomys'' **Subfamily † Palaeocastorinae ***†'' Palaeocastor'' ***†'' Capacikala'' ***†'' Pseudopalaeocastor'' ***Tribe † Euhapsini ****†'' Euhapsis'' ****†'' Fossorcastor'' **Subfamily † Castoroidinae ***†'' Priusaulax'' (placement in Castoroidinae questionable) ***Tribe † Nothodipoidini ****†'' Eucastor'' ****†'' Microdipoides'' ****†'' Nothodipoides'' ***Tribe † Castoroidini (paraphyletic) ****†'' Monosaulax'' ****†'' Prodipoides'' ****†'' Dipoides'' ****†''
Castoroides ''Castoroides'' (Latin: "beaver" (castor), "like" (oides)), or giant beaver, is an extinct genus of enormous, bear-sized beavers that lived in North America during the Pleistocene. Two species are currently recognized, ''C. dilophidus'' in the S ...
'' ****†'' Procastoroides'' ***Tribe † Trogontheriini ****†''
Trogontherium ''Trogontherium'' is an extinct genus of giant beavers, ranging from the Late Pliocene to the Late Pleistocene. It is not closely related to the North American giant beavers of the genus ''Castoroides''. Fossils of ''Trogontherium'' have been fou ...
'' ****†'' Boreofiber'' ****†'' Euroxenomys'' ****†'' Youngofiber'' ****†'' Asiacastor'' **Subfamily Castorinae ***†'' Chalicomys'' (also incorrectly "''Palaeomys''") ***†'' Steneofiber'' ***†'' Zamolxifiber'' ***†'' Romanofiber'' ***†'' Schreuderia'' ***†'' Sinocastor'' ***†'' Hystricops'' ***'' Castor'' - modern beavers ****
North American beaver The North American beaver (''Castor canadensis'') is one of two extant beaver species, along with the Eurasian beaver (''Castor fiber''). It is native to North America and introduced in South America ( Patagonia) and Europe (primarily Finland ...
, ''Castor canadensis'' ****
Eurasian beaver The Eurasian beaver (''Castor fiber'') or European beaver is a beaver species that was once widespread in Eurasia, but was hunted to near-extinction for both its fur and castoreum. At the turn of the 20th century, only about 1,200 beavers survi ...
, ''Castor fiber'' ****†''
Castor californicus ''Castor californicus'' is an extinct species of beaver that lived in western North America from the end of the Miocene to the early Pleistocene. The species was similar to but larger than the extant North American beaver, '' C. canadensis''. Re ...
''


References

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