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Class Mammalia
Order Rodentia
Family Castoridae


Castor sp.—American BeaversRegional Pleistocene distribution of Castor sp.


Late Blancan: 111 Ranch (Morgan and White 2005); Anza-Borrego (Murray 2008); Curtis Ranch (Lindsay 1984a); San Simon Fauna (Morgan and White 2005); Snowflake (Lindsay and Tessman 1974).

Literature. Lindsay 1984a; Lindsay and Tessman 1974; Morgan and White 2005; Murray 2008.


Castor californicus Kellogg 1911—Kellogg's BeaverRegional Pleistocene distribution of Castor californicus


Irvingtonian: El Golfo (Croxen et al. 2007: cf.).

Literature. Croxen et al. 2007;


Castor canadensis Kuhl 1820—American BeaverRegional Pleistocene distribution of Castor canadensis

Castor canadensis is the only living species in North America. This is the largest of the regional rodents, exceptionally reaching a weight of about 75 lbs.

American Beavers are closely associated with permanent water. Historically, they were common along the Colorado, Rio Grande and Pecos rivers, as well as smaller streams throughout the region. As most school children know, beavers build dams that trap stream water, providing a relatively deep pond that provides security for the lodge, a structure built largely of wood and having underwater entrances that lead to an area of the lodge that rises above the water. The pond also allows relatively safe access to the trees whose bark and other parts provide food for the beaver. Stores of sticks with bark attached may be stored in the bottom of the pond for later use.

This traditional picture fits well with small, mountain streams, but doesn't work well with rivers that usually are too broad to dam successfully. In such situations, beavers usually tunnel into a river bank that rises well above the normal water level. The entrance is submerged and the entrance tunnel rises to a chamber above the water, much as with the "traditional" lodge.

Dentary and teeth of fossil beaver (Castor canadensis)Beaver remains are rare in our region, where most sites either are some distance from expected habitat or unproductive for other than very large mammals. The large size of the beaver decreases the likelihood of a predator moving it any great distance to a cave situation.

The Early Irvingtonian record is from valley fill of the Rio Grande. The valley sediments were aggrading until well into the Irvingtonian NALMA before downcutting commenced, eventually forming the present valley. Presence of beaver indicates permanent water and presumably ample valley vegetation as a food source.

Fig. 1. The Early Irvingtonian specimen of Castor canadensis from the vicinity of La Union, Doña Ana Co., NM.

The tooth formula is 1/1 0/0 1/1 3/3 = 20. The teeth are complex and hypselodont (Figs. 2, 4). Expectably, the incisors are especially large and robust.

Left upper cheek teeth of Castor canadensis; anterior to left.Fig. 2. Left upper cheek teeth of the American Beaver, anterior to left.

The skull and post-cranial skeleton also are heavily built. Although the uninitiated could confuse the skull or teeth of the other large regional rodent, the porcupine, with that of the beaver, porcupines have rooted and somewhat less complicated cheekteeth, and the infraorbital foramen is huge. As can be seen in Fig. 3, that opening is almost minute in the beaver.

Anterior view of the skull of Castor canadensis Ventral view of the skull of Castor canadensis.

Fig. 3 (left). Anterior view of Castor canadensis skull showing the massiveness of the skull and the very small infraorbital foramena. Fig. 4 (right) Ventral view of the skull of Castor canadensis

Fig. 5 (below). Lateral view of Castor canadensis skull.

Anterior view of the skull of Castor canadensis


Early Irvingtonian: Adobe Ranch (Morgan and Lucas 2003).

Rancholabrean: Black Rock (Morgan and Lucas 2005).

Wisconsin/Holocene: Stanton's Cave (Olsen and Olsen 1984).

Literature. Morgan and Lucas 2003, 2005; Olsen and Olsen 1984.


Last Update: 1 Apr 2014