Chalicomys, Kaup, 1832

Casanovas-Vilar, Isaac & Alba, David M., 2011, The Never-Ending Problem of Miocene Beaver Taxonomy, Acta Palaeontologica Polonica 56 (1), pp. 217-220 : 217-218

Species of Chalicomys

According to Stefen (2009) and Mörs and Stefen (2010), the genus Chalicomys would only include the type species, C. jaegeri , and the questionable C. plassi . Their criteria therefore differ from that of Casanovas−Vilar et al. (2008), who distinguished three additional species within this genus. In particular, Mörs and Stefen (2010) reassigned C. catalaunicus to? Eucastor (Schreuderia) , transferred C. subpyrenaicus to Steneofiber , and synonymized C. batalleri with S. depereti . In the following lines we will review the species included within the genus Chalicomys . See Table 1 for a list of the species discussed and their synonymies.

Hugueney (1999) placed C. catalaunicus within the poorly known subgenus Schreuderia , which she considered a likely subgenus of the North American Eucastor . Schreuderia had been previously erected as a genus by Aldana Carrasco (1992) to accommodate S. adroveri , which strongly resembles Chalicomys but shows a markedly reduced M3. Hugueney (1999) noted that some molars of Schreuderia adroveri and Chalicomys catalaunicus show a tendency to display an S−pattern, leading her to place them into the same subgenus, which she considered to be related to castoroidines. This was later disputed by Korth (2001), who considered Schreuderia to be a castorine, probably even a subgenus of Chalicomys . Certainly, a few molars of C. catalaunicus display a tendency towards an S−pattern at particular wear stages, but generally the occlusal pattern is castorine−like. Moreover, the cheek teeth are hypsodont and the striae/iids are longer than in Steneofiber depereti , further displaying abundant cement in all the synclines/ids ( Fig. 1 ; see also Crusafont Pairó et al. 1948: pls. 5–8). These features strongly support the inclusion of this taxon in Chalicomys as a distinct and rather small−sized species, which partially overlaps with S. depereti but tends to be somewhat larger ( Fig. 2 ). A revision of the type species is clearly needed in order to assess the validity of the (sub)genus Schreuderia .

Mörs and Stefen (2010) considered Chalicomys batalleri a junior subjective synonym of S. depereti because they overlap in dental size and the p4 hypostriid in C. batalleri supposedly does not reach the crown base. However, the only known p4 of the latter species is still implanted in the mandible ( Casanovas−Vilar et al. 2008: figs. 2, 3) and the hypostriid continues into the alveolus, so that it is not possible to known whether it closed near the base of the tooth. Size is neither a distinguishing criterion, because C. batalleri overlaps with both S. depereti and Chalicomys jaegeri ( Fig. 2 ). On the contrary, C. batalleri differs from S. depereti by numerous features, namely: the occurrence of abundant cement in all the fossettes/ids (as in C. jaegeri ); the more well−developed hypostria and mesostria in the upper cheek teeth; and the presence of three moderately developed striae on the lingual side of the P4, while only a rather short mesostria is present in S. depereti (cf. Mörs and Stefen 2010: fig. 5W; Casanovas−Vilar et al. 2008: fig. 4E, K). Both Stefen (2009) and Mörs and Stefen (2010) further question the taxonomic value of enamel crenulations, which were considered to be diagnostic of C. batalleri . The latter authors argued that the holotype (a right hemimandible) belongs to a juvenile individual, because of the presence of crenulations. Nevertheless, the holotype shows the complete definitive dentition and the cheek teeth already display a moderate degree of wear, indicating that it belongs to an adult. Histological sections of extant beaver molars have shown that crenulations do in fact occur in old specimens at advanced wear stages ( Hünerman 1966; Kotsakis 1989), indicating that this feature cannot be solely indicative of a juvenile ontogenetic stage. Given all the reasons outlined above, we consider that C. batalleri is a valid species that should be retained in Chalicomys .

Concerning Chalicomys subpyrenaicus, Mörs and Stefen (2010) do not question the validity of this species, even though available specimens overlap in size with S. depereti . Nevertheless, given the fact that the hypostriids close above the crown base and that only mesostriids are well expressed on the lingual side, these authors transfer this species to Steneofiber . In spite of the correctness of the assertions above, it must be emphasized that, in C. subpyrenaicus , cement is present in all the fossettes/ids. Accordingly, we consider that it should be retained in Chalicomys .

Finally, C. plassi is known by only two teeth (the holotype, which is a p4, and a m3) from Dorn−Dürkheim ( MN11 , SW Ger−

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Figures

Fig. 1. IPS 31102, a left maxillary fragment with the upper incisor and P4–M2 of the castorid Chalicomys catalaunicus (Bataller, 1838) from Sant Quirze (MN7+8 from the Vallès−Penedès Basin, Catalonia, Spain). Note the abundant cement infilling all synclines.

Fig. 2. Scatterplot for the lower cheek teeth of all the Chalicomys species as compared to Steneofiber depereti. Schreuderia adroveri and Euroxenomys minutus rhenanus comb. nov. are also included for discussion (see text for details). A. m 1/2. B. m3 C. p4. The measurements for S. depereti from Hambach were taken from Mörs and Stefen (2010); for Chalicomys jaegeri from Eppelsheim from Stefen (2009) and from MB2B from Van de Weerd (1976); for Chalicomys plassi and E. minutus rhenanus from Dorn−Dürkheim from Franzen and Storch (1975); for S. adroveri from Torrent de Febulines from Aldana Carrasco (1992); for Chalicomys batalleri from ACM/C4–C2 and Chalicomys subpyrenaicus from Simorre from Casanovas−Vilar et al. (2008); and for Chalicomys catalaunicus from Sant Quirze from Crusafont Pairó et al. (1948) and Casanovas−Vilar et al. (2008). Acronyms for locality names are as follows: ACM/C4–C2, Abocador de Can Mata locality C4–C2; MB2B, Masía del Barbo 2B. All the measurements are in millimetres.