Castoridae

File:Biberschaedel-drawing.jpg

Skull of a beaver

Castoridae is a family of rodents that contains the two living species of beavers and their fossil relatives. A formerly diverse group, only a single genus is extant today, Castor. Two other genera of "giant beavers", Castoroides and Trogontherium, became extinct in the Late Pleistocene.

Characteristics

{{#invoke:Labelled list hatnote|labelledList|Main article|Main articles|Main page|Main pages}} 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.<ref name=EoM>Template:Cite book</ref> They have powerful incisors and the typical rodent dental formula: Template:Dentition2

Evolution

File:Euhapsis barbouri fossil (cropped).jpg

Euhapsis barbouri, collected in Wyoming. At the AMNH.

File:Skeleton of Castoroides ohioensis.jpg

Castoroides ohioensis

File:Eucastor tortus (fossil beaver) (cropped).jpg

Eucastor tortus, collected from Cherry County, Nebraska. At the AMNH.

The earliest castorids belong to the genus Agnotocastor, known from the late Eocene and Oligocene of North America and Asia.<ref name="ryb">Template:Cite journal</ref> 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.<ref name="korth1">Template:Cite journal</ref> 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.<ref>Template:Cite book</ref> 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 Template:Convert 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 it would have been a good swimmer, and it probably lived in swampy habitats.<ref>Savage, R.J.G., and Long, M.R. 1986. Mammal Evolution: an Illustrated Guide. Facts on File, New York, pp. 120–121 Template:ISBN.</ref>

Taxonomy

McKenna and Bell<ref>McKenna, Malcolm C., and Bell, Susan K. 1997. Classification of Mammals Above the Species Level. Columbia University Press, New York, 631 pp. Template:ISBN.</ref> divided Castoridae into two subfamilies, Castoroidinae and Castorinae. More recent studies <ref name="ryb" /><ref name="korth1"/> 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.<ref name="ryb" /> The Palaeocastorinae include beavers that are interpreted as fossorial (burrowing),<ref name="ryb" /> as are nothodipoidins and Migmacastor.<ref name="korth3">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.</ref> The following taxonomy is based on Korth<ref name="korth1" /><ref name="korth3" /><ref name="korth2">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.</ref> and Rybczynski,<ref name="ryb" /> 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
      • †Procastoroides
    • 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