Family of mammals
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
[
edit
]
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.
[1]
They have powerful
incisors
and the typical rodent
dental formula
:
Evolution
[
edit
]
The earliest castorids belong to the genus
Agnotocastor
, known from the late
Eocene
and
Oligocene
of
North America
and
Asia
.
[2]
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.
[3]
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.
[4]
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 2.5 m (8.2 ft) 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.
[5]
Taxonomy
[
edit
]
McKenna and Bell
[6]
divided Castoridae into two subfamilies, Castoroidinae and Castorinae. More recent studies
[2]
[3]
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.
[2]
The Palaeocastorinae include beavers that are interpreted as
fossorial
(burrowing),
[2]
as are nothodipoidins and
Migmacastor
.
[7]
The following taxonomy is based on Korth
[3]
[7]
[8]
and Rybczynski,
[2]
with preference given to the latter where these differ.
References
[
edit
]
Wikimedia Commons has media related to
Castoridae
.
- ^
Lancia, R.A.; Hodgdon, H.E. (1984). Macdonald, D. (ed.).
The Encyclopedia of Mammals
. New York: Facts on File. pp.
606?609
.
ISBN
0-87196-871-1
.
- ^
a
b
c
d
e
Rybczynski, N. (27 December 2006). "Castorid phylogenetics: implications for the evolution of swimming and tree-exploitation in beavers".
Journal of Mammalian Evolution
.
14
(1): 1?35.
doi
:
10.1007/s10914-006-9017-3
.
S2CID
33659669
.
- ^
a
b
c
Korth, W.W. (December 2001). "Comments on the systematics and classification of the beavers (Rodentia, Castoridae)".
Journal of Mammalian Evolution
.
8
(4): 279?296.
doi
:
10.1023/A:1014468732231
.
S2CID
27935955
.
- ^
Palmer, D., ed. (1999).
The Marshall Illustrated Encyclopedia of Dinosaurs and Prehistoric Animals
. London: Marshall Editions. p. 284.
ISBN
1-84028-152-9
.
- ^
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
.
- ^
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
.
- ^
a
b
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.
- ^
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.