Prosciurillus abstrusus Moore, 1958

Musser, Guy G., Durden, Lance A., Holden, Mary Ellen & Light, Jessica E., 2010, Systematic Review of Endemic Sulawesi Squirrels (Rodentia, Sciuridae), with Descriptions of New Species of Associated Sucking Lice (Insecta, Anoplura), and Phylogenetic and Zoogeographic Assessments of Sciurid Lice, Bulletin of the American Museum of Natural History 2010 (339), pp. 1-260 : 1-260

Prosciurillus abstrusus Moore, 1958

HOLOTYPE AND TYPE LOCALITY: The holotype of Prosciurillus abstrusus is an adult female (AMNH 101378) collected by Gerd Heinrich on January 4, 1932. A stuffed museum study skin and accompanying skull comprise the holotype. The skin is intact as is the cranium and the mandible; all teeth are present.

The type locality is Tanke Salokko, 1500 m, a high place on Pegunungan Mekongga, a mountain range in the southeastern peninsula of Sulawesi (see the maps and discussions in Heinrich [1932] and Stresemann [1940], and locality 1 in the gazetteer and map in figure 30), 03 ° 359S, 121 ° 159E (for the Pegunungan), Propinsi Sulawesi Tenggara, Indonesia.

EMENDED DIAGNOSIS: A small-bodied tree squirrel that in its morphology is most like Prosciurillus murinus among nannosciurine squirrels, but differs in having slightly duller upperparts and underparts, medial surfaces of the ears covered with white fur (but not extending beyond the pinnae rims to form tufts), absolutely larger skull, and relatively shorter rostrum but longer tooth rows (see section on comparisons).

GEOGRAPHIC AND ALTITUDINAL DISTRIBUTION: This squirrel is known only from Pegunungan Mekongga where it was collect- ed at 1500 m and 2000 m, elevations that bracket the transition between lower and upper tropical montane forest formations. Collections from lower elevations in tropical lowland evergreen rain forest in the foothills of Pegunungan Mekongga at 550 mm (Masembo) and on the coast 50 m (Wawo) between the Pegunungan and coast contained only Prosciurillus murinus .

Our knowledge of the montane fauna on Pegunungan Mekongga comes from the collecting efforts of G. Heinrich, his wife, and her sister at Tanke Salokko in 1932. Heinrich hunted birds and squirrels, his wife and sister trapped rats. Their samples of rats contained three species endemic to the mountain range and three others that are also found elsewhere. Taeromys arcuatus (collected at 1500 and 2000 m) and T. microbullatus (1500 m), along with Rattus salocco (1500 m), a member of the Rattus xanthurus group of species ( Musser and Carleton, 2005), are, like the tree squirrel Prosciurillus abstrusus , endemic to the mountain range (Musser, MS). Samples of four other species of murid rodents— Bunomys chrysocomus , B. penitus , Paruromys dominator , and Rattus hoffmanni —were trapped at 1500 and 2000 m. Bunomys chrysocomus , Paruromys dominator , and Rattus hoffmanni also range into the lowland forests at the base of the Mekongga range and are found throughout Sulawesi; Bunomys penitus is restricted to montane forest habitats and also occurs on the western mountain block of Sulawesi’s central core ( Musser and Holden, 1991; Musser and Carleton, 2005; Musser, MS).

Maxomys dollmani is another rat found at Tanke Salokko along with Prosciurillus abstrusus . Unlike the tree squirrel, however, the distribution of M. dollmani extends to the central part of the west-central region in the central core of Sulawesi where it is represent- ed by a single specimen ( Musser, 1969). Prosciurillus murinus occurs throughout that western mountain block, but P. abstrusus does not.

DESCRIPTION: Prosciurillus abstrusus is one of the smallest-bodied of the species of tree squirrels endemic to Sulawesi (length of head and body, 115–148 mm, length of hind foot, 35–38 mm; extremes from table 36), matched only by P. murinus in external dimensions (length of head and body, 102– 150 mm; length of hind foot, 32–38 mm; extremes from table 36). The moderately thick coat (12–15 mm) clothing upperparts of head and body is dark brown flecked with pale buff; the ventral fur is dark grayish white with a pale buff wash over the chest on some specimens. The tail is shorter than the length of the head and body (LT/LHB 5 81%) and the same color as the upperparts. Backs of the ears are densely covered with fine white hairs, forming a conspicuous white patch and providing the only contrast to the dark brown dorsum.

Females have three pairs of teats, one postaxillary pair and two inguinal pairs, the same combination possessed by all species of Prosciurillus .

Views of the small skull are illustrated in figures 12–14, where it is compared with skulls from other species of Prosciurillus ; cranial and dental measurements are summarized in table 38.

COMPARISONS: Prosciurillus abstrusus is most closely related to P. murinus and the two species are contrasted in the account of the latter.

GEOGRAPHIC VARIATION: This aspect is not possible to document at the present time because samples of P. abstrusus have been collected at only two elevations in one small area (Tanke Salokko) of the elongate Mekongga range.

ECOLOGY: No information is available covering these topics. Elsewhere on mainland Sulawesi, 1500 m, the lowest collection locality for P. abstrusus , would be in lower montane forest and 2000 m, the highest place where the species was obtained, would mark the beginning of the upper montane forest zone.

ECTOPARASITES: The sucking louse, Hoplopleura abstrusus , n. sp., uniquely parasitizes Prosciurillus abstrusus (see descriptions of lice in the following section). Also, ectoparasitic laelapid mites were recovered from six P. abstrusus pelts (AMNH 101353, 101355, 101357, 101359, 101361, and 101363), all collected at Tanke Salokko, Pegunungan Mekongga in southeastern Sulawesi at an elevation of 2000 m in 1931.

SYMPATRY: Prosciurillus abstrusus is the only squirrel that has been collected from the high reaches of Pegunungan Mekongga (tables 3, 5). It is replaced at lower elevations by its close relative, P. murinus (see that account). The only other member of Prosciurillus recorded from the southwestern peninsula is P. alstoni , a member of the P. leucomus group of species. It has been collected in the foothills of Pegunungan Mekongga at Masembo (550 m) and Mowewe (500 m) and at lower elevations on the western coastal plain at Wawo (50 m) and Lalolei (300 m). Samples of both P. alstoni and the smaller-bodied P. murinus have been taken at Masembo and Waso.

The large-bodied Rubrisciurus rubriventer has also been collected on the southeastern peninsula. Specimens are from Masembo, Wawo, and Lalolei, and from the slopes of Pegunungan Mekongga at 600 m and 1400 m. Whether the altitudinal ranges of P. abstrusus and R. rubriventer overlap between 1400 m and 1500 m or the distribution is parapatric in pattern is unknown.

SYNONYMS: No scientific name has been applied to a sample of P. abstrusus in the context of identifying a separate taxon. As part of his report on relationships among living members of Sciurinae , which was based on a survey of cranial traits, Moore (1959: 203) listed a specimen of ‘‘ Prosciurillus obscurus ’’ used in his synoptic set of specimens. The individual (AMNH 101354) is an example of P. abstrusus , and ‘‘ obscurus ’’ was simply a lapsus; the name has no nomenclatural status except as a nomen nudum.