Pteralopex, with one species and two subspecies, is the only megachiropteran genus endemic to the Solomons. Thomas (1888b:475) considered this unusual bat a relic, isolated from the time when pteropodids had cuspidate cheek-teeth. Although two workers (Matschie, 1899:11; Simpson, 1945:54) have synonymized Pteralopex with Pteropus, I regard Pteralopex as a morphologically distinct genus.
Individuals of Pteralopex can be distinguished from all species of Pteropus in the Solomon Islands by the following features: wing membranes originate along dorsal midline; braincase diminutive relative to rest of skull; sagittal crest pronounced; cheek-teeth cuspidate, broad and massive; i2 about 10 times larger than i1; upper canines with well-developed secondary cusp; postorbital process fused with zygomatic arch, forming complete bony ring around orbit.
Andersen (1909a:216; 1912:436) considered the relationships of Pteralopex and Pteropus and concluded that Pteropus pselaphon Lay, 1829, from the Sulphur Islands east of Taiwan, and Pteropus samoensis Peale, 1848, from the Samoan Islands, were the "closest" living relatives of Pteralopex. He stated further that Pteralopex "presents in fact scarcely a single character which is not either developed to a certain extent or at least distinctly foreshadowed in Pteropus pselaphon, pilosus, tuberculatus, or leucopterus." In summary, Andersen thought several species of Pteropus had undergone evolutionary development resembling that in Pteralopex, and that the latter, with its massive, cuspidate cheek-teeth, could be considered a highly modified Pteropus. For this hypothesis to be plausible, one must assume that the originally complex cheek-teeth of pteropodids became simple and, at least in the case of Pteralopex, secondarily became complex once again. According to present-day theory of evolutionary development, his hypothesis is improbable. Thomas (1888b:475) probably was correct when he considered Pteralopex an isolated relic.
Although Pteralopex usually is listed after Pteropus in phylogenetic arrangements (see, for example, Sanborn, 1931:21; Pohle, 1953:129; Laurie and Hill, 1954:40), I have placed Pteralopex before Pteropus.
Pteralopex atrata
Two subspecies of Pteralopex atrata (P. a. atrata and P. a. anceps) have been named; specimens of both are rare in museum collections. Thomas (1888a:155) described adults of atrata. Sanborn (1931:21) examined the one additional specimen known to me and reported that it agreed with Thomas' description.
Andersen (1909b:266) used a subadult female ("nearly fully grown") as the holotype of anceps. At least five additional specimens, all adults, of anceps now are housed in various collections. Judging from these individuals, the holotype of anceps was only four-fifths grown and because he used an immature individual, Andersen's (1912:437) criteria for distinguishing the two subspecies mostly are invalid.
Fig. 4. Distribution of Pteralopex atrata; P. atrata atrata (