Neacomys musseri, PATTON & DA SILVA & MALCOLM, 2000

PATTON, JAMES L., DA SILVA, MARIA NAZARETH F. & MALCOLM, JAY R., 2000, Mammals Of The Rio Juruá And The Evolutionary And Ecological Diversification Of Amazonia, Bulletin of the American Museum of Natural History 2000 (244), pp. 1-306 : 98-105

Neacomys musseri , new species

HOLOTYPE: MVZ 171486 (Museum of Vertebrate Zoology, University of California, Berkeley ), adult male, collected 14 July 1985 by James L. Patton (original number 11890); skin with skull and mandibles, in good con­ dition; and liver and kidney tissue, originally preserved in liquid nitrogen, maintained at –76°C in the frozen collection of the Museum of Vertebrate Zoology.

TYPE LOCALITY: 72 km NE Paucartambo (by road), at km 152, Departamento de Cusco, Perú, 1460m. Obtained in undisturbed upper tropical forest within the Manu Biosphere Reserve (figs. 66 and 67). The locality is just above San Pedro on the road from Paucartambo to Shintuya (in the Departamento de Madre de Dios) which courses down the steep valley of the Río Cosñipata in the watershed of the Río Alto Madre de Dios. Pacheco et al. (1993) provide a map of collecting localities, including this one, within the Manu Biosphere Reserve.

DIAGNOSIS: This is a small­bodied mouse (fig. 68) characterized by its small and delicate cranium (figs. 69, 70, and 71); short maxillary toothrow; apparently unique presence (among other species in the genus) of the derived cephalic arterial system (as in Oligoryzomys ; see Carleton and Musser 1989), in which the squamosal­alisphenoid groove and sphenofrontal foramen are absent (indicating that the supraorbital branch of the stapedial artery is missing), but large stapedial foramen persists (pattern 2, of Voss 1988; see also Carleton and Musser, 1989) and first upper molar with a deep anteromedian flexus divides the procingulum into anterolabial and anterolingual conules (fig. 72)

PARATYPES: Twelve others, in addition to the holotype, from the type locality: MVZ 171481 (adult male), 171482 (adult male) 171483 (adult male), 171484 (adult female) 171485 (adult male), 171487 (adult male) 171488 (adult male), and 171489 (adult female); fluid: MVZ 172328 (adult male) 172329 (adult male), 172330 (adult female) 172331 (adult male), all collected in July 1985. Additional referred specimen: MNFS 1395 (adult female, skin with skull), collect­ ed in February 1992 from opposite Igarapé Porongaba, left bank Rio Jurua´ , Acre, Brazil (to be cataloged in the Coleção de Mamíferos, INPA, Manaus, Brazil). Tissues (frozen and maintained at –76°C and/or in ethyl alcohol) are preserved from all specimens except those in fluid .

MEASUREMENTS OF HOLOTYPE: TOL, 153 TAL, 83; HF, 22; E, 13; CIL, 18.88; ZB 11.44 ; MB, 9.93; IOC, 4.51; RL, 7.33; NL, 7.80; RW­1 , 4.03 ; RW­2 , 3.30 ; OL, 7.22; D, 5.51; MTRL, 2.65; IFL, 2.99; PBL, 8.49; AW, 4.01; OCB, 5.24; BOL, 2.97; MPFL, 2.64; MPFW, 1.45; ZPL, 1.97; CD, 8.03.

ADDITIONAL MEASUREMENTS: See table 24.

DESCRIPTION AND COMPARISONS: Neacomys musseri is significantly larger in nearly all external and cranial dimensions than the second small­bodied species described below, but smaller than N. spinosus (table 24). The three species, however, have the same general proportions, as indicated by bivariate plots of external and cranial variables (fig. 73). The difference in size and great similarity in body proportions are highlighted by the significant differences in scores between the three species for PC­1 but generally not for subsequent PC axes (table 24). However, the three taxa are readily separable by a discriminant function analysis using log­transformed

cranial variables (fig. 73, lower right; see table 25 for standardized character coefficients). Predicted group membership of individual specimens to their respective a priori groups is perfect, with individual posterior probabilities of 0.893 or higher. This species has generally the same spinose fur with color and tones as in other congeners both large and small, from Amazonia. A delicate mouse, N. musseri has a slender tail that is weakly bicolored dark brown above, paler below, obviously scaled in appearance, and clothed in short hairs. Scale rows are narrow­ er than in N. spinosus , but similar in size to those of the second small­bodied species from the Rio Juruá (averaging 16 per cm versus 13 in spinosus ). The hind feet are narrow and elongate, with proportionately long digits, but similar in this respect to other species All three species have six plantar tubercles of similar size and proportions. Cranially, N.

musseri is unique among Neacomys from western Amazonia in its derived cephalic arterial system, lacking the supraorbital branch of the stapedial artery. Other species of Neacomys from western Amazonia (including N. spinosus and the second species described below, and the small­bodied forms from northern Perú and Ecuador or the Rio Jaú [clades 3 and 6 in figs. 62 and 63]) possess the squamosal­alisphenoid groove and sphenofrontal foramen indicative of the primitive cephalic arterial pattern. All species in the genus have rather delicate skulls, with rounded crania, diverging and well­developed supraorbital ridges that extend onto the temporal region, shallow zygomatic notches with relatively narrow but vertical zygomatic plates with rounded superior margins, weakly developed zygomatic arches, short and relatively broad rostra, opisthodont upper incisors, long palates with short incisive foramina, pronounced postpalatal pits, broad mesopterygoid fossae, and broad and moderately excavated parapterygoid fossae The incisive foramen of N. musseri differs slightly, but consistently, in shape from those of other species, being widest at its midpoint and converging posteriorly, rather than diverging gradually to reach its widest dimension at its posterior margin, as in the second species described below (fig. 74). The posterior margin of the foramen nearly reaches the level of the first upper molars in N. musseri , but is widely separated from them in second species described below. The bullae are globular but small; the stapedial foramen is enlarged and obvious, indicative of a welldeveloped stapedial artery (as in Oligoryzomys ; Carleton and Musser, 1989). Aside from the overall size of the molars (table 24) and the depth of the anteromedian flexus (­id) the occlusal patterns of the three species are closely similar (fig. 72). The molar teeth are pentalophodont, with high and narrow cusps in the unworn condition, with well­developed anterolophs (­ids), mesolophs (­ids) and posterolophs (­ids) on both first and second molars, and a small but moderately complicated third molar similar to that of Microryzomys (Carleton and Musser, 1989) . The procingulum of the first upper and lower molars is divided into anterolabial and anterolingual conules (­ids) by a deeply excised anteromedian flexus (­id). In this respect, N musseri differs strongly from N. spinosus which appears to lack a demonstrable anteromedian flexus (­id). The anteromedian flexus (­id) of the other small­bodied species from the Rio Juruá basin (described below is not as well developed as it is in N. spinosus (fig. 72).

DISTRIBUTION AND HABITAT: This species is known only from the type locality and from the headwaters of the Rio Juruá in western Brazil adjacent to the Peruvian border. The habitat at the type locality is upper tropical forest (‘‘Bosque húmedo subtropical’’ of the Holdridge [1967] system; Tosi, 1960; see figs. 66 and 67) ; that in the headwaters of the Rio Juruá is lowland rainforest, part of the phytogeographic domain termed ‘‘Floresta Tropical Aberta’’ (Projeto RadamBrasil, 1977). It is likely that specimens referred to Neacomys tenuipes from Cusco Amazónico, Departamento de Madre de Dios in southeastern Perú, by Woodman et al. (1991) represent this species, but we have not examined them. No small­bodied spiny mice that could represent this species have been recorded as yet from Bolivia (Anderson, 1997) .

REPRODUCTION AND LIFE HISTORY: The series of specimens from the type locality in southeastern Perú was collected in July during the dry season. All individuals are adults with most being old adults, judging from toothwear and pelage characteristics, but none were in reproductive condition. Each of the six males had small (4–5 mm), nonscrotal testes ; both females were parous, one with obvious placental scars suggesting a prior

breeding effort. The single specimen from the upper Rio Juruá in western Brazil is a subadult female captured in February, during the rainy season. This specimen has subadult, nonspinous pelage remaining on the rump, although it was pregnant with two near­term embryos, each 13 mm in crown­rump length.

ETYMOLOGY: Named in honor of Guy G. Musser for his long friendship and many outstanding contributions to our understanding of the systematics and evolutionary diversification of muroid rodents, including those of the Neotropical region.

KARYOTYPE: 2n = 34, FN = (64–68), with 15 pairs of biarmed chromosomes, grading in size from large to small, and two pairs of small uniarmed elements (fig. 75A). Since only a single female was examined, the sex chromosomes are unknown, but presumably the X­chromosome would represent one of the medium­sized biarmed elements characteristic of other known karyotypes in the genus (see below and Gardner and Patton, 1976). This complement contrasts sharply with the 2n = 64 and nearly uniarmed karyotype of N. spinosus (see Gardner and Pat­ ton, 1976, and fig. 75D) and differs substantially from that of the second small­bodied species from the Rio Jurua´, described next.