Castoridae

Taxobox
name = Castoridae
fossil_range = Late Eocene - Recent

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image_width = 200px
image_caption = American Beaver, "Castor canadensis"
regnum = Animalia
phylum = Chordata
classis = Mammalia
ordo = Rodentia
subordo = Castorimorpha
familia = Castoridae
familia_authority = Hemprich, 1820
subdivision_ranks = Genera
subdivision = †"Migmacastor"
†"Agnotocastor"
†"Neatocastor"
†"Anchitheriomys"
†"Propalaeocastor"
†"Oligotheriomys"
†"Palaeocastor"
†"Capacikala"
†"Pseudopalaeocastor"
†"Euhapsis"
†"Fossorcastor"
†"Priusaulax"
†"Eucastor"
†"Microdipoides"
†"Nothodipoides"
†"Monosaulax"
†"Prodipoides"
†"Dipoides"
†"Castoroides"
†"Procastoroides"
†"Trogontherium"
†"Boreofiber"
†"Euronexomys"
†"Youngofiber"
†"Asiacastor"
†"Palaeomys"
†"Chalicomys"
†"Steneofiber"
†"Zamolxifiber"
†"Romanofiber"
†"Schreuderia"
†"Sinocastor"
†"Hystricops"
"Castor"

The family Castoridae contains the two living species of beaver and their fossil relatives. This was once a highly diverse group of rodents, but is now restricted to a single genus, "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 wintercite book |editor=Macdonald, D.|author= Lancia, R.A. & Hodgdon, H.E.|year=1984 |title= The Encyclopedia of Mammals|publisher= Facts on File|location=New York|pages= 606-609|isbn= 0-87196-871-1] . They have powerful incisors and the typical rodent dental formula: dentition2|1.0.1-2.3|1.0.1.3

Evolution

The earliest castorids belong to the genus "Agnotocastor",known from the late Eocene and Oligocene of North America and Asia (Rybczynski, 2007). Other early castorids included genera such as "Steneofiber", from the Oligocene and Miocene of Europe, the earliest member of the subfamily Castorinae, which contains castorids closely related to living beavers (Korth, 2002). Their teeth were not well suited to gnawing wood, suggesting that this habit evolved at a later point, but they do appear adapted to semi-aquatic living [cite book |editor=Palmer, D.|year=1999 |title= The Marshall Illustrated Encyclopedia of Dinosaurs and Prehistoric Animals|publisher= Marshall Editions|location=London|pages= 284|isbn= 1-84028-152-9] . Later, such early species evolved into forms such as "Palaeocastor" from the Miocene of Nebraska. "Palaeocastor" was about the size of a muskrat, and dug corkscrew-shaped burrows up to convert|2.5|m|ft|abbr=on deep.

Giant forms evolved in the Pleistocene, 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 that it would have been a good swimmer, and it probably lived in swampy habitats (Savage and Long, 1986).

Taxonomy

McKenna and Bell (1997) divided Castoridae into two subfamilies, Castoroidinae and Castorinae. More recent studies (Korth, 2002; Rybczynski, 2007) have recognized two additional subfamilies of basal castorids, Agnotocastorinae and Palaeocastorinae, which is followed here. Within the family, Castorinae and Castoroidinae are sister taxa (Korth, 2002; Rybczynski, 2007); 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 (Rybczynski, 2007). Palaeocastorinae includes beavers that are interpreted as fossorial (burrowing) (Rybczynski, 2007), as are nothodipoidins and "Migmacastor" (Korth, 2007b). The following taxonomy is based on Korth (2002, 2007a,b) and Rybczynski (2007), with preference given to the latter where the 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"
****†"Procastoroides"
***Tribe †Trogontheriini
****†"Trogontherium"
****†"Boreofiber"
****†"Euronexomys"
****†"Youngofiber"
****†"Asiacastor"
**Subfamily Castorinae
***†"Palaeomys" or †"Chalicomys"
***†"Steneofiber"
***†"Zamolxifiber"
***†"Romanofiber"
***†"Schreuderia"
***†"Sinocastor"
***†"Hystricops"
***"Castor" - modern beavers

References

*Korth W.W., 2002. Comments on the systematics and classification of the beavers (Rodentia, Castoridae) "Journal of Mammalian Evolution" 8(4):279-296.
*Korth 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.
*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.
*McKenna, Malcolm C., and Bell, Susan K. 1997. "Classification of Mammals Above the Species Level." Columbia University Press, New York, 631 pp. ISBN 0-231-11013-8.
*Rybczynski N., 2007. Castorid phylogenetics: implications for the evolution of swimming and tree-exploitation in beavers "Journal of Mammalian Evolution" 14(1):1-35.
*Savage, R.J.G., and Long, M.R. 1986. "Mammal Evolution: an Illustrated Guide." Facts on File, New York, pp.120-121 ISBN 0-8160-1194-X.

See also

*Beaver