Nyctinomops sp.—Big and Pocketed Free-tailed Bats // Tadarida sp.—Guano Bats // Tadarida brasiliensis—Brazilian Free=tailed Bat // Tadarida constantinei—Constantine's Free-tailed Bat
Molossid bats are widespread in both the New and the Old World. Several occur in the U.S., but only members of the genera Nyctinomops and Tadarida are known as fossils from our region. Two species of Nyctinomops inhabit the region at present (N. macrotis and N. femorosacca) and one species of Tadarida, the Brazilian Free-tailed Bat, is common. The genus Eumops occurs in southern parts of the region, but has not been identified as fossils.
Synonyms. Tadarida macrotis
Harris (1993c) reported Nyctinomops macrotis from two early Wisconsin or early mid-Wisconsin sites on the basis of two complete humeri and the proximal end of a radio-ulna. Further work throws doubt on the identification. Though apparently molossid, the humeri from Sabertooth Camel Maze are roughly 10% longer than N. macrotis and show qualitative differences. The radio-ulna is not clearly molossid.
The other species of Nyctinomops currently known from the region is the Pocketed Free-tailed Bat (Nyctinomops femorosaccus). It is marginal in our region, being known only from Hidalgo and Eddy counties in New Mexico (Frey 2004) and from Big Bend in Texas (Schmidly 2004). It has not been recognized as a fossil in the region. Skeletal material of Eumops, a large molossid, is not available to me at this time.
Fig. 1. Fossil molossid humeri (top, third from top) compared to the humerus of Nyctinomops macrotis (second from top); proximal radio-ulna of fossil from Lost Valley and of N. macrotis (bottom). Scale in mm.
Early/Early-Mid Wisconsin: Lost Valley (Harris 1993c); Sabertooth Camel Maze (Harris 1993c).
Literature. Frey 2004; Harris 1993c; Schmidly 2004.
Tadarida is a widespread genus, occurring in the Old World as well as the New. As with other members of the family, the tail when the animal is at rest extends beyond the interfemoral membrane—thus part of the tail is "free," giving rise to the common name of free-tailed bats.
Our Southwestern species are colonial, though only the Brazilian Free-tailed Bat has historically had colonies numbering into the 10s of millions.
Late Wisconsin: Bat Cave, Grand Canyon National Park (Mead et al. 2005); Muskox Cave (Logan 1981).
Literature. Logan 1981; Mead et al. 2005.
Both Carlsbad Caverns and U-Bar Cave have supported maternity colonies of these bats historically and both have large numbers of fossil bats. The other cave sites do not appear to have had such colonies, but probably have been utilized during migration.
Rancholabrean: Papago Springs Cave (Skinner 1942: ? sp.) Rejected
Mead et al. (2005) note that Skinner's specimens have been reexamined and do not represent Tadarida brasiliensis.
Early/Early-Mid Wisconsin: Lost Valley (Harris 1993c: cf.).
Mid Wisconsin: U-Bar Cave (Harris 1987).
Late Wisconsin: Lower Sloth Cave (Logan 1983); TT II (Harris 1993c); U-Bar Cave 13-14 ka (Harris 1989); U-Bar Cave 14-15 ka (Harris 1989); U-Bar Cave 15-18 ka (Harris 1989); U-Bar Cave 18-20 ka (Harris 1989).
Late Wisconsin/Holocene: Balcony Room (Harris 1993c); Carlsbad Caverns (Baker 1963).
Literature. Baker 1963; Harris 1987, 1989, 1993c; Logan 1983; Mead et al. 2005; Skinner 1942.
Baker (1963:38) notes in passing, after mentioning a radiocarbon date from New Cave, that "the extinct freetail is found also in the Carlsbad Caverns" and (p.39) "Some sections of the Bat Cave [a room in Carlsbad Caverns] contain deposits of fossilized guano, capped by several inches of flowstone, and scattered through it are the bones of the extinct Pleistocene freetail." Baker's article is written for lay speleologists and he cites no authority for the statements, thus I have listed it only hesitantly.
Lundberg and McFarlane (2006) dated the fossil-bearing deposit in Slaughter Canyon Cave as a minimum of 209 ± 9 ka since it underlies a calcite layer of that date as determined by U-Th dating.
Rancholabrean: Slaughter Canyon Cave (New Cave) (Lawrence 1960).
Wisconsin: Carlsbad Caverns (Baker 1963)
Literature. Baker 1963; Lawrence 1960; Lundberg and McFarlane 2006.
Last Update: 11 Mar 2013