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.

Characters (from Korth 2001): Intermediate to large rodents; skeletons generally robust to massive, developing fossorial or semiaquatic adaptations in some lineages. Skull generally low, broad, and robust with broad zygomata; postorbital process lacking; sciuromorphous zygomasseteric structure, with infraorbital foramen low on rostrum; sciurognathous; digastric (symphyseal) eminence on mandible; interorbital foramen posterior to optic foramen. Incisor microstructure uniserial; dental formula I11 C00 P(2)11 M33; cheek teeth lophate, forming series of transverse or oblique re-entrant valleys (flexi) or elongated fossettes of enamel; cheek teeth at least mesodont in crown height, commonly attaining hypsodonty; crowns of molars tapering towards base of crown (shortening anteroposteriorly with wear).

    |--Agnotocastorinae K04
    |    |--Neatocastor hesperus K04
    |    |--Hystricops K04
    |    `--Agnatocastor B74
    `--+--Anchitheriomyinae [Anchitheriomyini] K04
       |    |--+--Miotheriomys Korth 2004 K04
       |    |  |    `--*M. stenodon Korth 2004 K04
       |    |  `--Oligotheriomys K04
       |    |       |--O. magnus K04
       |    |       `--O. primus K04
       |    `--+--Propalaeocastor K04
       |       `--Anchitheriomys Roger 1898 K04
       |            |--A. fluminis K04
       |            |--A. nanus Korth 2004 K04
       |            |--A. senrudi K04
       |            `--A. stouti K04
       `--+--Palaeocastor MHL03 [Palaeocastorinae K04]
          |    `--P. fossor MHL03
          |--Castor B75 [Castorinae K04]
          |    |--C. canadensis B75
          |    |    |--C. c. canadensis B75
          |    |    `--C. c. missouriensis Bailey 1919 B75
          |    `--C. fiber B74
          |         |--C. f. fiber USDI77
          |         `--C. f. birulai USDI77
          `--Castoroidinae K04
               |  i. s.: Eucastor K04
               |--Monosaulax Stirton 1935 [Castoroidini] K04
               |    |--*M. pansus K04
               |    |--M. baileyi Korth 2004 K04
               |    `--M. skinneri K04
               `--Trogontheriini K04
                    |--Trogontherium Fischer von Waldheim 1809 P04 P04
                    `--Euroxenomys Samson & Radulesco 1973 K04
                         `--E. wilsoni Korth 2001 K04

*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.

[B74] Bugge, J. 1974. The cephalic arterial system in insectivores, primates, rodents and lagomorphs, with special reference to the systematic classification. Acta Anatomica 87 (Suppl 62): 1-160.

Korth, W. W. 2001. Comments on the systematics and classification of the beavers (Rodentia, Castoridae). Journal of Mammalian Evolution 8 (4): 279-296.

[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.

[MHL03] Meng, J., Y. Hu & C. Li. 2003. The osteology of Rhombomylus (Mammalia, Glires): Implications for phylogeny and evolution of Glires. Bulletin of the American Museum of Natural History 275: 1-247.

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

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


  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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