Castor, WITH

Stefen, Clara, 2009, Intraspecific variability of beaver teeth (Castoridae: Rodentia), Zoological Journal of the Linnean Society 155 (4), pp. 926-936 : 931

COMPARISON OF CASTOR WITH FOSSIL BEAVERS

The size range from juvenile to fully grown individuals is about 5.7 mm for incisor length in recent Castor : this is equivalent to about 57% of the maxl of the incisor ( Table 1). For the length of the upper incisor of A. suevicus , the range is 7.9 mm, which is equivalent to nearly 57% of the maxl of the tooth. This is very similar to modern Castor , and thus the observed size differences in the small sample of fossil teeth of A. suevicus can well be attributed to postnatal growth, as suggested by Stefen & Mörs (2008).

The range of the length of upper incisors differs between these two species: about 55% maxl in Castor , and about 44% in Anchitheriomys ( Fig. 2, Table 1). The range in length of upper and lower incisors together is 62% maxl of the incisor in S. eseri , which is even larger than in modern Castor . The few studied specimens of the larger capybara ( H. hydrochaeris ) show a range in the length of upper and lower incisors of over 80% of maxl.

The size ranges of mandibular tooth rows for different fossil beavers and C. fiber are illustrated in Figure 3. For all of the species studied, a noticeable variation in tooth row length can be observed: about 11 mm (30% maxl) in C. fiber , 11.8 mm (30% maxl) in A. suevicus , and 60 mm (71% maxl) in H. hydrochaeris . For the samples of the early Miocene S. eseri and S. castorinus studied, the range of the mandibular tooth row is around 4 mm and 17% of maxl. In all species, the low size ranges were observed in m1/2 and M1/2 lengths and widths, respectively.

In recent Castor , no pattern in the form and distribution of enamel folds and islands on the chewing surface, which could be used as clear age indicators, were recognizable ( Fig. 4 ). There are only a few features, like the closing of the para-, meso-, or metafossette, and, at the latest, hypofossette, that can be easily determined.

Figures

Figure 4. Mandibular tooth rows of Castor fiber at different ages. A, 94/104, 5-months old; B, 94/190, 39-months old; C, 94/107, 48-months old; and D, 94/65, 80-months old. All are from the Zoological Collection University Halle-Wittenberg. Scale bar: 5 mm.