Scotoecus olduvensis, Gunnell & Butler & Greenwood & Simmons, 2015

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 : 10-13

† Scotoecus olduvensis , new species

Figures 6 , 7

Cf. Pipistrellus (Scotozous) rueppelli, Butler and Greenwood, 1965: 15 ; Butler, 1978: 65; Gunnell, 2010: 588.

HOLOTYPE: NMT.004/Bat, left dentary with c1–m3 (fig. 6B; see table 2 for measurements).

REFERRED SPECIMEN: NMT.024/Bat, left distal humerus (also includes right proximal humeral fragment), FLK Main Dig 1, Z level (see table 1 for measurements).

ETYMOLOGY: Named for Olduvai Gorge, Tanzania.

TYPE LOCALITY: Tanzania: Olduvai Gorge, Bed I, FLK NI, Layer 3.

DIAGNOSIS: Similar to extant Scotoecus albofuscus (fig. 6A) and S. hindei (fig. 6C) but differs from both in being, on average, 12% larger in tooth dimensions; S. olduvensis further differs from S. hindei in having: c1 lacking a buccal cingulid and anterolingual and posterolingual basal cuspules; a relatively longer posterior shelf that is not notched; p2 relatively larger compared to p4; p4 more similar in size to p2 (not larger as in extant taxa); p4 with a buccal cingulid lacking or very weak, a more robust cusp, and a lingual cingulid lacking an anterolingual extension. S. olduvensis further differs from S. albofuscus in having: c1 more robust, lacking a heavy lingual cingulid, with a more posteriorly extended posterior shelf that is not notched; p4 more similar in size to p2 (not larger as in extant taxon), lacking a lingual crest off the posterior part of the cusp that terminates in a posterior lingual extension of the lingual cingulid, which lacks an anterolingual extension, but has a better developed posterior shelf; S. olduvensis further differs from both extant taxa in having: p2 lacking a distinctive anterior extension of the anterolingual cingulid that forms a protrusion that fits into the notch of the canine posterior shelf; m3 with a somewhat lower hypoconid and entoconid and lacking a hypoconulid.

DESCRIPTION: The lower canine of S. olduvensis is robust and relatively broad with a convex anterior surface, a flat posterior surface, and a lingual cingulid continuous with a low, moderate posterior shelf. The posterior shelf is overlapped by p2, which is single rooted and slightly wider than long but essentially circular in occlusal view. Anteriorly p2 overlaps the posterior shelf of the canine and has a continuous cingulid that is heaviest buccally. Lower p4 is similar to p2 but is slightly larger and relatively wider than long. It has a developed lingual cingulid, but the buccal cingulid is very weak. Like p2 there is only a single cusp developed on p4 that is slightly more robust than that found in p2. The lower molars are very similar to those of S. hindei and S. albofuscus : in having very tall and prominent talonid cusps and high entocristids, in being nyctalodont with well-developed crests, and in having relatively strong buccal cingulids. The lower molar trigonids are nearly as wide as talonids, in contrast to the living species in which the trigonid is noticeably more restricted buccolingually. The bases of the hypoconid and entoconid are inflated producing a relatively narrow and restricted talonid basin compared to the extant taxa.

The distal end of NMT.024/Bat, the left distal humerus that we refer to S. olduvensis (fig. 7, bottom row), has a narrow but robust capitulum that is slightly angled and not offset from the shaft. The lateral capitular tail, even though somewhat broken, appears to have been much less broad than trochlear surface and is essentially continuous with the capitulum (shallow to absent groove). The trochlear groove is weak and the trochlear surface is relatively wide and robust with a sharply defined trochlear lip. The medial epicondylar process is broken and the groove on lateral surface of epicondyle is weak to absent.

Also included with NMT.024/Bat is a potentially associated right proximal humerus. The head of this specimen is ovate and somewhat angled. The proximal margin of the head does not extend beyond the proximal extent of trochiter and is about at the same height as the proximal extent of the lesser trochanter. There is a high (anteriorly) deltopectoral crest. It is relatively long and sharply defined with a slight overhanging lip developed medially. The deltopectoral crest curves toward base of trochiter and anteriorly encloses a moderately deep fossa.

No other fossils of Scotoecus have been described or figured (Simmons and Gunnell, in prep.).

Figures

FIGURE 6. Left lower dentitions of Scotoecus in occlusal view. A, S. albofuscus (AMNH 241054); B, S. olduvensis, n. sp. (NMT.004/Bat, Holotype, cast); C, S. hindei (AMNH 241055).

FIGURE 7. Left distal humerus of Scotoecus hindei (NHMUK 63.1151) compared with Scotoecus olduvensis, n. sp. (NMT.023/Bat), in A, anterior, B, posterior, C, medial, and D, lateral views.