Miniopterus cf. M. schreibersi ( Kuhl, 1817 )

Gunnell, Gregg F., Butler, Percy M., Greenwood, Marjorie & Simmons, Nancy B., 2015, Bats (Chiroptera) from Olduvai Gorge, Early Pleistocene, Bed I (Tanzania), American Museum Novitates 2015 (3846), pp. 1-35 : 23-28

Miniopterus cf. M. schreibersi ( Kuhl, 1817)

Figures 14 , 15

Miniopterus cf. schreibersi, Butler, 1978: 65 ; Gunnell, 2010: 588.

REFERRED SPECIMENS: NMT.007/Bat, right dentary p3–4 (p4 now lost but shown in drawings of MG), from FLK NI, layer 5, Tr. IV; NMT.011/Bat, left and right distal humeri, from FLK NI, layer 3; NMT.017/Bat, right distal humerus, from FLK NI, layer 2; NMT.019/Bat, right proximal humerus, FLK NI, layer 2 (maybe not Miniopterus , poorly preserved); NMT.022/Bat, left proximal humerus, right distal humeri (2), humeral shaft, from FLK, Main Dig Z level; NMT.038/Bat, right distal humerus, from FLK NI, layer 3, Tr. IV (see tables 1 and 2 for measurements).

DESCRIPTION AND DISCUSSION: One dental specimen representing Miniopterus cf. M. schreibersi is known from the Olduvai sample, a right dentary (NMT.007/Bat) that originally had p3–4 and the alveoli for all other teeth preserved. The p3 is double rooted with a single, lingually placed cusp that has a sloping, convex buccal surface and straight, flat lingual surface. A continuous, weakly developed cingulid is present that is developed into a tiny posterolingual extension. In detailed morphology this p3 is quite similar to that of extant M. schreibersi (fig. 14). The p4 was originally in place in this specimen and based on the available drawings (see fig. 14) it was very similar to p4 of extant M. schreibersi . It shared the presence of a tall, pointed protoconid and a broad but short talonid shelf formed by the distal cingulid with the extant taxon. Both extinct and extant specimens lack any indication of a para- or metaconid and both have well-developed labial and lingual cingulids that join anteriorly with the labial cingulid sloping ventrally from anterior to posterior.

The dentary has a large mental foramen beneath the c1–p2 roots. Based on alveoli, p2 was single rooted as in living M. schreibersi . The i3 alveolus is slightly separated from the conjoined i1–2 alveoli and is larger than either of the other incisor alveoli as in extant Miniopterus species, and all incisor alveoli are aligned mesiodistally. There is a smaller mental foramen below the i1 alveolus on anterior surface of dentary.

The humeral fragments of the Olduvai Miniopterus specimens are very similar in size and morphology to the humerus of extant Miniopterus schreibersi . The proximal end of the humerus in Olduvai Miniopterus specimens has a moderately high (anteriorly) deltopectoral crest that is relatively long and sharply defined. It has a distinct, overhanging medial lip. The crest curves to the base of the trochiter and anteriorly encloses a relatively deep intertrochanteric fossa. The head of the humerus is ovate and angled. The proximal margin of the head does not extend as far proximally as the trochiter, instead extending proximally about the same distance as the lesser trochanter.

The distal end of the Miniopterus humerus has a narrow, rounded capitulum that is slightly angled and is not offset from shaft. The lateral capitular tail is somewhat broader than the trochlear surface and is separated from the capitulum by a deep and distinct groove. In contrast, the trochlear groove is faint and the trochlear surface is relatively narrow with a sharply defined trochlear lip. The medial epicondylar process is broken in all Olduvai specimens, but, judging by what remains, it would have been distinct and would have extended well beyond the trochlear ridge as it does in extant Miniopterus (fig. 15). The groove on the lateral surface of the epicondyle is absent, but there is a distinct fossa that occurs on the lateral surface below the root of the epicondylar process. Like all other Miniopterus species, the specimens from Olduvai have well developed and deep olecranon fossae (see fig. 15B, top and bottom), a feature not commonly found in bats.

These Olduvai specimens are assigned to Miniopterus cf. M. schreibersi because they are very similar in morphological detail to the humerus of the living taxon. However, Miniopterus schreibersi is not the only similar-sized Miniopterus species to occupy sub-Saharan Africa today. Therefore it is possible that the Olduvai species might be more closely related to one of the other species, especially M. africanus or M. inflatus , given that both of these species have been confused with M. schreibersi in the past ( Simmons, 2005). We have chosen to follow Butler’s (1978) original assignment of these specimens to Miniopterus cf. M. schreibersi but acknowledge that more complete specimens are needed to assess the precise relationship of the Olduvai Miniopterus species to living members of that genus.

The African fossil record of Miniopterus is limited to the record from Olduvai, two Pliocene records from South Africa ( Pocock, 1987) and a late Pliocene record from Morocco ( Gunnell et al., 2011). The South African Pliocene occurrences are recorded in faunal lists, but the specimens upon which the assignments are based have never been described or figured.

Figures

FIGURE 14. Comparison of extant Miniopterus schreibersi (A, C, E – AMNH 161928, right i1–m3, photographs) and extinct Miniopterus cf. M. schreibersi (B, D, F – NMT.007/Bat, right p4–m1, drawings) in A–B, occlusal, C–D, lateral, and E–F, medial views.

FIGURE 15. Right distal humerus of extant Miniopterus schreibersi (NHMUK 19.7.7.2417) compared with fossil Miniopterus cf. M. schreibersi (NMT.011A/Bat) in A, anterior, B, posterior, C, medial, and D, lateral views.