Myotis cf. bechsteinii (Kuhl, 1818)

Popov, Vasil V., 2004, Pliocene small mammals (Mammalia, Lipotyphla, Chiroptera, Lagomorpha, Rodentia) from Muselievo (North Bulgaria), Geodiversitas 26 (3), pp. 403-491 : 430-433

Myotis cf. bechsteinii (Kuhl, 1818) ( Fig. 16 )

MATERIAL EXAMINED. — 15 mandibular fragments (1 with p4 and m1, 2 with p4, m1 and m2, 1 with m1-m2, 5 with m2-m3, 2 with m1, 1 with m2, 3 with m3) (Ms320-334), 15 c1 (Ms335-336), 1 p4 (Ms337), 4 m 1 (Ms338), 7 m 2 (Ms339), 2 m 3 (Ms340), 39 C1 (Ms378), 1 P4 (Ms342), 7 M1-2 (Ms343-344), 1 M3 (Ms345).

MEASUREMENTS. — See Table 5.

DESCRIPTION AND COMPARISON

Mandible: the horizontal ramus is rather massive. The mental foramen lies between the roots of the canine and p2 as in the recent M. emarginatus (Geoffroy, 1806) and M. nattereri (Kuhl, 1818) , while in the modern comparative material of M. bechsteinii (Kuhl, 1818) it is situated under the p2. The anterior margin of the horizontal branch of mandible is more oblique in lateral view than in the modern M. emarginatus . In this respect it is similar to M. bechsteinii .

c1: the posterior shelf of the cingulum is not well developed; its distal part is not curved upwards as in the modern M. emarginatus , M. nattereri , and especially in M. bechsteinii .

p3: judging by the size and position of the alveolus, this premolar should be relatively large, situated close to p4, in such a way that their crowns were probably contiguous, differing in this respect from the modern M. emarginatus in which the premolars are loosely spaced.

p4: this tooth is rectangular in occlusal view with a medial constriction and, in crown outline, it resembles the respective teeth of the recent M. emarginatus and M. bechsteinii . However, the posterior edge has no impression for m1 as in the recent M. bechsteinii . In the modern species, this feature resulted from a strong mesio-distal compression of the tooth row anterior portion. Another consequence of this compression is the strong overlapping between the crowns of p3 and p 4 in modern M. bechsteinii . The arrangement of p3, p4 and m 1 in the fossil material corresponds more or less to that of the recent M. emarginatus . In particular, in both forms the p4 and m1 barely contact at the margins of the cingula. On the other hand, the available p4s differ from the respective teeth of M. emarginatus in having a less developed antero-labial cingular shelf, and a labial cingulum not considerably bent upwards, being only gently curved as in the recent M. nattereri .

m1 and m2: these myotodont molars are rather condensed antero-posteriorly as compared with the modern M. bechsteinii but not so much as in the available comparative material of M. nattereri . In this respect, they are similar to the molars of the recent M. emarginatus , but the fossil teeth are larger. The anterior half of the labial cingulum is thicker than in the recent M. emarginatus . In this respect, it is somewhat similar to the present-day M. nattereri .

m3: myotodont. The talonid is rather broad and massive. In this feature, the fossil species is quite different from the modern species M. bechsteinii and M. emarginatus in which the talonid is conspicuously smaller. The fossil material is somewhat similar to the comparative sample of M. nattereri , but in this species the talonid is shorter and more gracile. In all recent species, the lateral margin of the crown (between the trigonid and talonid) is deeply concave in occlusal view, while in the fossil teeth this concavity is less pronounced.

C1: this tooth is rather elongated. The anterolingual ridge of the crown is indistinct and rounded and the respective groove is shallow. In this respect, it is similar to the modern M. emarginatus . In contrast, M. bechsteinii possesses a rather sharp ridge along the antero-lingual side of the crown.

P4: the anterior cingulum is poorly developed in contrast to the modern M. bechsteinii and M. emarginatus .

M1-M2: with protoconule, paraloph, metaloph, and metaconule (well pronounced on M2) as in the recent M. emarginatus . These elements are also present in the comparative material of the modern M. bechsteinii but variably pronounced and generally poor. Although similar in size to the molars of the recent Nyctalus leisleri (Kuhl, 1817) , the fossil specimens differ in having interruption of the lingual cingulum at the base of the protocone; this cingulum is complete in the recent comparative sample of N. leisleri . In this respect the fossil teeth are comparable with the recent M. bechsteinii and other Myotis species.

M3: although more massive, it is similar to the respective tooth of M. emarginatus .

REMARKS

The comparisons of the sample from Muselievo with the Pliocene species M. gundersheimensis Heller, 1936 from Poland (Podlesice) and Hungary (Osztramos 9) ( Godawa 1993) show that, although similar in size, this species has shorter molars. M. gundersheimensis seems more specialized than the recent M. bechsteinii in having shorter c1-p4 row, being similar in this respect to the middle Pleistocene Myotis kretzoii Topál, 1981 . The last species, however, differs from both M. gundersheimensis and M. bechsteinii in having three cusps on the lower incisors ( Topál 1981). Unfortunately, M. gundersheimensis Heller, 1936 , originally described from Gundersheim ( Germany, MN15b, Koenigswald & Tobien 1990), is, up to now, very superficially known on evidence of a mandibular material, and it is impossible to compare the upper molars which are of a particular phylogenetic and taxonomic importance. Nevertheless, according to the multivariate analysis on the mandibles of fossil and recent Myotis species , presented by Topál (1985), M. bechsteinii and M. gundersheimensis seem very similar.

The fossil molars from Muselievo are nearly identical in dimensions with the comparative sample of the recent M. bechsteinii from Bulgaria ( Figs 11; 12 ). In this respect it is also similar with the Pleistocene remains of this species from La Fage ( France) ( Mein 1975). The fossil form from Muselievo, however, has a more massive mandible, more complicated occlusal surface of the upper molars, relatively wider talonid on m3, more loosely arranged lower premolars, and considerably longer upper canines ( Fig. 13C ). As mentioned above, these differences indicate that the fossil form is at a lower level of specialization in comparison with the modern species. In its massive mandible the form from Muselievo is similar to Myotis bechsteinii robustus Topál, 1963 , described from the early Pleistocene of Hungary (Repashuta) ( Topál 1963a). This form is also reported from the early Pleistocene of the isle of Malta ( Storch 1974) and Hundsheim ( Austria) ( Rabeder 1972). The individual teeth from these localities correspond in size to the remains from Muselievo and to the recent comparative material from Bulgaria. Unfortunately, the data on the dimensions of upper canines of the forms from Malta and Austria are scarce.

The above comparisons indicate that the early fossil forms similar in size to the recent M. bechsteinii need detailed study, especially in order to reveal their relationships with the present-day species. For the time being, on the basis of the similarity in size and morphology of the molars, I tentatively refer the material from Muselievo to M. bechsteinii . The long upper canines probably indicate that we deal with a relatively primitive and unspecialized form.

Figures

FIG. 16. — Myotis cf. bechsteinii (Kuhl, 1818); A, right P4, Ms342, occlusal view; B, right M1, Ms343-3, occlusal view; C, right M2, Ms343-2, occlusal view; D, right M3, Ms345, occlusal view; E, right fragment of mandible with p4-m3, Ms322, occlusal view; F, the same, labial view. Scale bar: 1 mm.

FIG. 12. — Scatter diagrams showing length (L) and width (W) of upper molars (mm) of fossil and recent Myotis spp.; A, M1; B, M2; C, M3. For explanations see Fig. 11.

FIG. 13. — Scatter diagrams showing length (L) and width (W) of p4 (A), lower canine (B), and upper canine (C) (mm) of fossil and recent Myotis spp. For explanations see Fig. 11.