Molossus molossus (Pallas)

Simmons, Nancy B. & Voss, Robert S., 1998, The mammals of Paracou, French Guiana, a Neotropical lowland rainforest fauna. Part 1, Bats, Bulletin of the American Museum of Natural History 237, pp. 1-219 : 159-160

Molossus molossus (Pallas)

Figures 61–63

VOUCHER MATERIAL: 18 females (AMNH *267242, *267243, *267244, *267245, *267246, *267247, *267252, *267253, *267254, *267255, *267256, *269102; MNHN 1995.964, *1995.965, *1995.966, *1995.967, *1995.968, *1995.969), 8 males (AMNH *266374, *267241, *267248, *267250, *267251, *267261; MNHN *1995.970, *1995.971), and 1 individual of indeterminate sex (MNHN 1995.963; individual found dead); see table 63 for measurements.

IDENTIFICATION: As described above, our collections from Paracou include two small Molossus species, M. barnesi and M. molossus , that can be easily distinguished based on features of the pelage and dentition, and by craniodental and external measurements. Our voucher material of Molossus molossus corresponds closely with Husson’s (1962, 1978) description of this species in Surinam, although our 25 adults include a few individuals that are slightly smaller than any in his series.

The subspecies nomenclature for Molossus molossus is complex (see discussion in Dolan, 1989) and has been confused by the inclusion of several distinct species (e.g., M. aztecus , M. barnesi , M. coibensis ) in recent classifications (e.g., Freeman, 1981; Hall, 1981; Koopman, 1994). Husson (1962) restricted the type locality of M. molossus to Martinique, so M. m. molossus is clearly the appropriate name for populations in the southern Lesser Antilles ( Hall, 1981; Dolan, 1989). Hall (1981) and Dolan (1989) also applied this name to popluations on the north coast of South America (e.g., in Venezuela). However, Dolan (1989: 64) noted that, should additional collecting demonstrate differences between populations in the Lesser Antilles and those on the adjacent mainland, then the correct subspecies name for the latter ‘‘would be M. m. minor Kerr, 1792 , with M. longicaudatus Geoffroy, 1805 , M. pygmaeus Miller, 1900 , and M. daulensis J. A. Allen, 1916 as junior synonyms.’’

We compared measurements of our Paracou material (table 63) with published measurements of several large series of M. mol­ losus from populations in the Lesser Antilles (in Genoways et al., 1981) and found few differences. Measurements of males and females from Paracou fall within the range of variation reported for each sex in the Lesser Antilles. However, mean values of several measurements (forearm length, postorbital breadth, mastoid breadth, zygomatic breadth, maxillary toothrow length) for Paracou females slightly exceed (by 0.1–0.2 mm) the corresponding means reported by Genoways et al. (1981) for Lesser Antillean females. No such pattern was seen with male measurements. In our view, this is trivial geographic variation that does not deserve recognition at any taxonomic level. Although we do not advocate any trinomial nomenclature for M. molossus , if subspecies were to be recognized the French Guianan population would presumably be referable to the nominate form in recognition of the similarities described above.

One final problem involves the specimens referred to this species by Brosset and Charles­Dominique (1990: 547), who noted that ‘‘the Molossus molossus from French Guiana are remarkable by their small size.’’ Examination of the measurements they published for five specimens from Piste St.­Élie reveals that one male and two females are much smaller than any in our Paracou sample of M. molossus for forearm length and length of the maxillary toothrow. Measurements of these same individuals, however, compare favorably with our specimens of M. barnesi . For example, female forearm length at Paracou is 34.4–35.0 mm for barnesi and 37.6– 39.7 mm for molossus ; the two small females from Piste St.­Élie have forearms measuring 34.5–35.2 mm ( Brosset and Charles­Dominique, 1990). The small male from St.­Élie has a forearm of 35.0 mm, compared to 37.6–39.9 mm for molossus males at Paracou. By contrast, two larger specimens from St.­Élie fall well within the range of variation we observed for molossus at Paracou. Plausibly, Brosset and Charles­Dominique’s sample of ‘‘ Molossus molossus ’’ is composed of individuals representing both M. molossus and M. barnesi .

FIELD OBSERVATIONS: We recorded 222 captures (probably including some recaptures) of Molossus molossus at Paracou, of which 93 were in ground­level mistnets, 104 were in elevated nets, and 24 were at roosts; additionally, we were given a skull found in a storage shed. Of the 93 ground­level mistnet captures, 6 were in manmade clearings and 87 were over roadside puddles. Of the 104 elevated net captures, 97 were made between 7 and 23 m over a narrow dirt road and 7 were made at 35–38 m over a treefall in well­drained primary forest.

Two separate roosting groups were found simultaneously occupying a small wooden shed in a large clearing: one group of 11 females and 4 males was found under the corrugated metal roof, and another group of 8 males and 1 female was found in a box halffilled with tools on the floor (one unsexed bat escaped from this group). All of the bats found in the shed were adults.

Figures

Fig. 61. Dorsal (A) and ventral (B) views of the skull of Molossus barnesi (AMNH 269105; female) from Paracou. Dorsal (C) and ventral (D) views of the skull of M. molossus (AMNH 269102; female) from Paracou. Note species differences in size, relative breadths of the postorbital region and braincase, and incisor morphology. Scale bars = 10 mm.

Fig. 62. Lateral views of the skull and lower jaw of (A) Molossus barnesi (AMNH 269105; female) and (B) M. molossus (AMNH 269102; female). Scale bars = 10 mm.

Fig. 63. Anterior view of the skull and upper dentition of (A) Molossus barnesi (AMNH 269105; female) and (B) M. molossus (AMNH 269102; female). Note the species difference in shape of the upper incisors, which are spatulate in barnesi but taper to pincerlike points in molossus. Scale bars = 5 mm.