Other than the dinosaur-laden Mesozoic Era, the time period which receives the most attention from the general public is probably the Pleistocene. This isn’t entirely unjustified, because the Pleistocene is rich with charismatic megafauna. It seems like practically every group of mammals has a giant Pleistocene representative, some of which are truly gigantic (at least by land mammal standards). But one of my favorites has always been one of the smaller examples of the megafauna, the giant beaver Castoroides ohioensis.
In the image above, the mounted Castoroides at Earlham College’s Joseph Moore Museum is shown next to its modern relative, the beaver Castor canadensis. Castoroides may not have been as gigantic as a mammoth or mastodont, but as a rodent the size of a black bear it was still an impressive animal. For many years Castoroides was the largest known rodent, but it has since been surpassed by several recent South American discoveries.
Castoroides ranged widely across North America, and is known from several localities in Virginia. One of those sites is the famous deposit in Saltville, which is the source of the Castoroides material in the VMNH collection:
This is a nearly complete right innominate (fused ilium, ischium, and pubis), shown in lateral view. Note the size; this element is over 30 cm long. Giant beavers really are giant!
This somewhat rough-looking bone is the anterior surface of the seventh cervical (neck) vertebra. Note the irregular shape along the bottom margin. Here’s the same specimen in ventral view:
See the short, dark, horizontal lines on each side of the midline? That’s a gap between two bones. This specimen is actually two vertebrae, the 7th cervical and the 1st thoracic, fused together. The rough surface is composed of osteophytes, secondary bone growths that are associated with injuries, arthritis, or other bone pathologies.
Both of these specimens were reported by McDonald and Freeman (2009). They suggested that fused cervicals or anterior thoracics may be common in both Castor and Castoroides (the Earlham Castoroides also has some fused vertebrae), which could be related to similar habits. There has been some debate as to whether or not Castoroides ate large woody plants to the same degree as Castor, so it would be interesting to see some further work on beaver vertebral pathologies.
These were apparently the first two Castoroides specimens ever reported from Saltville, and as far as I know they are still the only giant beaver remains from the site.