North American beaver Castor canadensis, photographed by Ginger Holser.

Belongs within: Castorimorpha.

The Castoridae include the beavers, large Holarctic rodents. Among the modern fauna, beavers comprise only two surviving species known for their practice of building complex semi-aquatic nests (dams). These are the North American beaver Castor canadensis and the European beaver C. fiber; the North American beaver has also been introduced to some parts of Europe. Fossil species of beaver were more diverse, including burrowing as well as semi-aquatic forms. The most basal subgroup is the latest Eocene to late Miocene subfamily Agnotocastorinae, characterised by a relatively long rostrum, parallel upper tooth rows, and procumbent incisors with a smooth enamel surface.

    |  i. s.: Procastoroides G88
    |--Agnotocastorinae K04
    |    |--Neatocastor hesperus K04
    |    |--Hystricops K04
    |    `--Agnotocastor Stirton 1935 SM93
    |         |--A. aubekerovi X96
    |         |--A. coloradensis Wilson 1949 X96
    |         |--A. galushai Emry 1972 X96
    |         `--A. praetereadens Stirton 1935 X96
    `--+--Anchitheriomyinae [Anchitheriomyini] K04
       |    |--+--Miotheriomys Korth 2004 K04
       |    |  |    `--*M. stenodon Korth 2004 K04
       |    |  `--Oligotheriomys K04
       |    |       |--O. magnus K04
       |    |       `--O. primus K04
       |    `--+--Propalaeocastor kumbulakensis K04, X96
       |       `--Anchitheriomys Roger 1898 K04
       |            |--A. fluminis K04
       |            |--A. nanus Korth 2004 K04
       |            |--A. senrudi K04
       |            `--A. stouti K04
       `--+--+--Steneofiber Geoffroy 1833 R08, SM93
          |  |    |--S. pansus Cope 1874 C77
          |  |    `--S. viciacensis C77
          |  `--Castor Linnaeus 1758 L58 [Castorinae K04]
          |       |--C. accessor G88
          |       |--C. canadensis FS15
          |       |    |--C. c. canadensis B75
          |       |    `--C. c. missouriensis Bailey 1919 B75
          |       |--C. fiber Linnaeus 1758 L58
          |       |    |--C. f. fiber USDI77
          |       |    `--C. f. birulai USDI77
          |       `--C. moschatus Linnaeus 1758 L58
          |--Castoroidinae K04
          |    |  i. s.: Eucastor K04
          |    |         Dipoides intermedius R08, TH03
          |    |--Trogontheriini K04
          |    |    |--Trogontherium Fischer von Waldheim 1809 P04
          |    |    `--Euroxenomys Samson & Radulesco 1973 K04
          |    |         `--E. wilsoni Korth 2001 K04
          |    `--Castoroidini K04
          |         |--Castoroides ohioensis FS15
          |         `--Monosaulax Stirton 1935 K04
          |              |--*M. pansus K04
          |              |--M. baileyi Korth 2004 K04
          |              `--M. skinneri K04
          `--Palaeocastorinae [Capacikalini] X96
               |  i. s.: Pseudopalaeocastor Martin 1987 X96
               |           `--P. barbouri (Peterson 1905) (see below for synonymy) X96
               |--+--Palaeocastor Leidy 1869 X96
               |  |    |--P. nebrascensis (Leidy 1856) (see below for synonymy) X96
               |  |    `--P. peninsulatus (Cope 1881) [=Steneofiber peninsulatus] X96
               |  `--Capacikala Macdonald 1963 X96
               |       |--C. gradatus (Cope 1879) [=Steneofiber gradatus] X96
               |       `--C. parvus Xu 1996 X96
               `--+--+--Nannasfiber Xu 1996 X96
                  |  |    |--*N. ostellatus Xu 1996 X96
                  |  |    `--N. osmagnus Xu 1996 X96
                  |  `--Fossorcastor Martin 1987 X96
                  |       |--F. brachyceps Martin 1987 [=Capatanka brachyceps] X96
                  |       |--F. fossor (Peterson 1905) (see below for synonymy) X96
                  |       `--F. greeni Martin 1987 X96
                  `--+--Capatanka Macdonald 1963 X96
                     |    |--C. cankpeopi Macdonald 1963 X96
                     |    `--C. minor Xu 1996 X96
                     `--Euhapsis Peterson 1905 X96
                          |--E. breugerorum Maritn 1987 X96
                          |--E. ellicottae Martin 1987 X96
                          |--E. gaulodon Matthew 1907 X96
                          |--E. luskensis Xu 1996 X96
                          `--E. platyceps Peterson 1905 X96

Fossorcastor fossor (Peterson 1905) [=Steneofiber fossor, Palaeocastor fossor; incl. P. (Capatanka) magnus Martin 1987, P. major Romer & McCormack 1928, Steneofiber simplicidens Matthew 1907, P. simplicidens] X96

Palaeocastor nebrascensis (Leidy 1856) [=Steneofiber nebrascensis; incl. Capacikala sciuroides Macdonald 1963] X96

Pseudopalaeocastor barbouri (Peterson 1905) [=Steneofiber barbouri, Palaeocastor barbouri; incl. Pa. milleri Olson 1940] X96

*Type species of generic name indicated


[B75] Bowles, J. B. 1975. Distribution and biogeography of mammals of Iowa. Special Publications, The Museum, Texas Tech University 9: 1–184.

[C77] Cope, E. D. 1877. Report upon the extinct Vertebrata obtained in New Mexico by parties of the expedition of 1874. Geographical Surveys West of the One Hundredth Meridian 4 (2): i–iv, 1–370.

[FS15] Faurby, S., & J.-C. Svenning. 2015. A species-level phylogeny of all extant and late Quaternary extinct mammals using a novel heuristic-hierarchical Bayesian approach. Molecular Phylogenetics and Evolution 84: 14–26.

[G88] Gray, J. 1988. Evolution of the freshwater ecosystem: the fossil record. Palaeogeography, Palaeoclimatology, Palaeoecology 62: 1–214.

[K04] Korth, W. W. 2004. Beavers (Rodentia, Castoridae) from the Runningwater Formation (Early Miocene, Early Hemingfordian) of western Nebraska. Annals of Carnegie Museum 73 (2): 1–11.

[L58] Linnaeus, C. 1758. Systema Naturae per Regna Tria Naturae, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. Tomus I. Editio decima, reformata. Laurentii Salvii: Holmiae.

[P04] Popov, V. V. 2004. Pliocene small mammals (Mammalia, Lipotyphla, Chiroptera, Lagomorpha, Rodentia) from Muselievo (north Bulgaria). Geodiversitas 26 (3): 403–491.

[R08] Rybczynski, N. 2008. Woodcutting behavior in beavers (Castoridae, Rodentia): estimating ecological performance in a modern and a fossil taxon. Paleobiology 34 (3): 389–402.

[SM93] Stucky, R. K., & M. C. McKenna. 1993. Mammalia. In: Benton, M. J. (ed.) The Fossil Record 2 pp. 739–771. Chapman & Hall: London.

[TH03] Tedford, R. H., & C. R. Harington. 2003. An Arctic mammal fauna from the Early Pliocene of North America. Nature 425: 388–390.

[USDI77] United States Department of the Interior. 1977. Endangered and threatened wildlife and plants—republication of list of species. Federal Register 42: 36420–36431.

[X96] Xu, X. 1996. Castoridae. In: Prothero, D. R., & R. J. Emry (eds) The Terrestrial Eocene–Oligocene Transition in North America pp. 417–432. Cambridge University Press.

Last updated: 31 January 2022.


  1. Is there no genus called Casteroides? Where does Casteroidinae get its stem name from?

  2. I'm sure there is a Castoroides. Most of the listings on these pages are incomplete: after all, I'm only one person.


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