Eptesicus isabellinus

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 : 13-15

Cf. Eptesicus isabellinus

Figure 8

Eptesicus cf. hottentotus, Butler, 1978: 65 .

REFERRED SPECIMEN: NMT.032/Bat, right distal humerus, FLK NI, layer 6, 1964 (see table 1 for measurements).

DESCRIPTION AND DISCUSSION: Olduvai specimen NMT.032/Bat represents a vespertilionid humerus very similar in size and morphology to that of extant Eptesicus isabellinus . NMT.032/Bat (fig. 8, bottom row) has a narrow but robust capitulum that is not angled or offset from shaft. The lateral capitular tail is much less broad than the trochlear surface, and is separated from the capitulum by a shallow groove. A trochlear groove is absent and the trochlear surface is relatively wide and robust with a sharply defined trochlear lip. The medial epicondylar process is low and robust and does not extend distally beyond the trochlear ridge. Groove on the lateral surface of epicondyle is weak to absent. These are all features typical of Eptesicus .

The taxonomy of Eptesicus isabellinus is unresolved at the moment, but it appears to be the North African representative of the Eptesicus serotinus radiation sensu lato ( Simmons, 2005). However, it is not clear whether E. isabellinus can be maintained as a species separate from E. serotinus ( Simmons, 2005) . We have chosen to retain it as distinct subject to revision of circumMediterranean Eptesicus species.

NMT.032/Bat very closely resembles E. isabellinus (NHMUK 19.7.7.1160, fig. 8, top row) in nearly every detail of size and morphology. The fossil specimen has a slightly less distally extended epicondylar process and the distal end is slightly deeper anteroposteriorly. NMT.032 differs from Eptesicus furinalis (AMNH 278332) only in being relatively larger with a slightly broader capitulum and lacking any groove between the capitulum and trochlea. The lateral ridge is slightly broader than in the extant taxon but otherwise similar.

The only records of Eptesicus fossil material from Africa all come from southern Africa ( Hendey, 1981; Pocock, 1987; Avery, 1998), mostly from the early to late Pliocene deposits, and they are based on teeth and jaws that are not directly comparable to the specimen described here. Eptesicus is a common element of other Plio-Pleistocene faunal communities and is widespread across the northern continents during this time period (Simmons and Gunnell, in prep.).

Figures

FIGURE 8. Right distal humerus of Eptesicus isabellinus (NHMUK 19.7.7.1160) compared with cf. Eptesicus isabellinus (NMT.032/Bat) in A, anterior, B, posterior, C, medial, and D, lateral views