Nycticeinops serengetiensis, 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 : 17-19

† Nycticeinops serengetiensis , new species

Figures 9 , 10

Cf. Nycticeius (Scoteinus) schlieffeni, Butler and Greenwood, 1965: 15 ; Butler, 1978: 65; Gunnell, 2010: 588.

HOLOTYPE: NMT.005/Bat, right dentary with p4–m1 and alveoli for all other teeth (fig. 9F–H; see table 2 for measurements).

REFERRED SPECIMENS: NMT.001/Bat, left dentary with m2–3 and alveoli for all anterior teeth, from FLK NI, layer 123; NMT.006/Bat, left edentulous dentary preserving all tooth alveoli, from FLK NI, layer 1; NMT.013/Bat, left distal humerus, from FLK NI, layer 2; NMT.015/Bat, right distal humeri (3), from FLK NI, layer 123; NMT.016/Bat, left and right distal humeri, from FLK NI, layer 3; NMT.023/Bat, right distal humerus (and most of shaft), from Main Dig, FLK 1, Z level; NMT.025/Bat, left distal humerus, from FLK1, Z level; NMT.034/Bat, left proximal humerus, from FLK NI, layer 1, Tr. IV, 1964; NMT.035/Bat, right distal humeri (2), from FLK NI, layer 5, Tr. IV, 1964; NMT.036/Bat, left distal humerus, from FLK NI, layer 2, Tr. V; NMT.037/Bat, left and right distal humeri, from FLK NI, layer 1, Tr. III (see table 1 for measurements).

ETYMOLOGY: Named for the famed Serengeti region in northern Tanzania where Olduvai Gorge is located.

TYPE LOCALITY: Tanzania: Olduvai Gorge, Bed I, FLK NI, layer 5, Tr. IV.

DIAGNOSIS: Differs from extant Nycticeinops schlieffeni (the only other recognized species of the genus) in having teeth on average 20% larger; p4 relatively taller and labiolingually narrower with a relatively longer talonid shelf; m1 with more curved paracristid and more angled entocristid, hypoconulid relatively lower and talonid basin more deeply excavated; m2 with relatively lower hypoconulid; and m3 with heavier anterolabial cingulid.

DESCRIPTION AND DISCUSSION: All three of the known fossil jaws have slightly different arrangements of their incisor alveoli. The holotype of N. serengetiensis ( NMT.005/Bat) has a small i3 alveolus directly in front of the canine alveolus while a slightly larger i2 alveolus is anteromedial to that of i3 and directly posterior to an equally large i1 alveolus. NMT.001/Bat has a similar arrangement except that the i1 alveolus is noticeably larger than either the i2 or i3 alveoli and is placed somewhat more laterally, producing a triangular arrangement of alveoli. The edentulous dentary of N. serengetiensis (NMT.006/Bat) is more similar to the holotype except that the alveoli of i2 and i3 are nearly mediolaterally opposite one another and the i2 alveolus is smaller. The arrangement of incisors in extant Nycticeinops schlieffeni (e.g., AMNH 257406) is somewhat different in that the i2 alveolus is not as far medial but instead forms part of a non-arcuate row of incisors running from the canine to the midline of the jaw with i1 most anterior and i3 most posterior. The offset arrangement found in N. serengetiensis may, in part, be due to the larger teeth of the fossil form and subsequent crowding of teeth in the jaw (although certain other extant vespertilionids also have a similar arrangement of incisor alveoli to those seen in N. serengetiensis ; N.J. Czaplewski, personal commun.). As further evidence of this crowding, the p4 of NMT.005/Bat is very closely appressed to the m1 with the m1 overlapping the p4 talonid shelf.

The dentaries of N. serengetiensis are all broken posteriorly but preserve enough of the ascending ramus to show that it rose dorsally at a shallower angle than that in N. schlieffeni , in which the ramus rises more steeply and then turns anteriorly (fig. 9A). Like in the extant taxon, there is typically a single mental foramen located beneath the area of contact between c1–p3, but it is relatively larger in N. serengetiensis , which occasionally has a smaller foramen located more anteriorly as well (fig. 9D). The dentaries of N. serengetiensis also differ from the modern species by having their ventral borders gently sloping dorsally from posterior to anterior and then ending anteriorly by turning dorsally. In N. schlieffeni the dorsal border of the dentary angles dorsally from posterior to anterior and forms a continuous surface with no angulation producing a jaw that is deeper beneath p4 than it is beneath m3.

The Olduvai collection includes 13 distal humeri and one proximal humerus that we refer to N. serengetiensis based on their similarity to those of extant N. schlieffeni . NMT.034/Bat is a left proximal humerus that has a semi-rounded and slightly angled head that does not extend quite as far proximally as the trochiter but does extend slightly past the lesser trochanter. The deltopectoral crest is high anteriorly and fairly long, and has a sharply defined edge with a slightly overhanging lip developed medially. The crest curves toward the base of the trochiter and anteriorly encloses a moderately deep intertrochanteric fossa.

The distal humerus of N. serengetiensis is characterized by a relatively narrow capitulum that is neither angled nor offset from the shaft. The lateral capitular tail is much less broad than the trochlear surface and is separated from the capitulum by a very shallow groove. The trochlear groove is weak and the trochlear lip is sharply defined. The medial epicondyle has a small process that extends distally only slightly beyond trochlear ridge. The groove on lateral surface of epicondyle is moderately developed.

Other than the specimens described here no other fossils of Nycticeinops are known (Simmons and Gunnell, in prep.).

Figures

FIGURE 9. Mandible of Nycticeinops schlieffeni (AMNH 257406, photographs) in A, lateral and B, occlusal views compared with Nycticeinops serengetiensis, n. sp. (drawings). C–E, N. serengetiensis, left dentary with m1–2 and all anterior alveoli (NMT.001/Bat) in C, occlusal, D, lateral and E, medial views. F–H, Holotype of N. serengetiensis, right dentary with p4–m1 with all other alveoli (NMT.005/Bat) in F, occlusal, G, lateral, and H, medial views.

FIGURE 10. Right distal humerus of Nycticeinops schlieffeni (NHMUK 32.7.463) compared with Nycticeinops serengetiensis, n. sp. (NMT.015/Bat), in A, anterior, B, posterior, C, medial, and D, lateral views.