Rhipidomys leucodactylus Tschudi, 1845

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 : 169

Rhipidomys leucodactylus Tschudi, 1845

TYPE LOCALITY: ‘‘im Oststriche’ ’, the region east of the Andean Cordillera in central Peru´ ; restricted to Montaña de Vitoc in the Chanchamayo Valley , Departamento de Junín, Peru´, by Tribe (1996) .

DESCRIPTION: This is a large­bodied species, with head­and­body length exceeding 175 mm, on average (table 46). The tail is especially long, averaging 122% of headand­body length, and terminates in an elongated and distinctive tuft of hair averaging 27 mm (range 20–36 mm; fig. 109). Even two subadult individuals (age class 2) have a distinct pencil, with lengths of 16 and 17 mm, respectively, more than twice the length of the tail tuft of R. gardneri . The tail is also well haired along its entire length, with individual hairs extending over more than three scale rows. Although partially hidden from view by hairs, the tail scales appear rather coarse, and average 11 rows per cm. The dorsal pelage varies from grayish to orangish brown in color; it is thick and somewhat woolly in texture. The ventral pelage is graybased throughout in all specimens, with either off­white or pale buffy tips; three specimens have a buffy suffusion on the upper thorax. The hind foot is large, distinctly broadened, with a dark patch covering most of the dorsal surface of the foot and extending onto the digits; only the terminal ungual tufts are white in most specimens. The skull (fig. 107) is large, averaging 36 mm in condyloincisive length, with shallow zygomatic notches, a broad and relatively short rostrum, a long maxillary toothrow averaging 6.3 mm, and a relatively short but conspicuously broad mesopterygoid fossa, the anterior bor­ der of which is typically smoothly arched and without a median projection (fig. 111).

DISTRIBUTION AND HABITAT: We caught all but one of our specimens in mature terra firme forest in canopy platform traps; the other individual was obtained by hand from a tree hole. We recorded the species at five localities, three on the right bank and two on the left, from the Upper Central, Lower Central and Mouth sections of the river (see ‘‘Specimens Examined,’’ below).

REPRODUCTION: Both female specimens were nulliparous, with thin and threadike uteri lacking any vascularization, and ovaries lacked obvious mature follicles. Interestingly, one female was a relatively young individual (age class 3) but still molting from subadult to adult pelage across the shoulder region; the other was an older adult (age class 4). As limited as these data are, they do suggest that breeding is delayed in this species relative to other sympatric sigmodontines. This may account, at least in part, for the relative rarity of these rats.

KARYOTYPE: We have chromosomal data from seven of the eight specimens collected All are uniform in possessing a diploid number of 44 with fundamental number of 46 The karyotype (fig. 112A) consists of 19 pairs of acrocentric autosomes grading in size from large to small, and with the first pair distinctly larger than the next, and two pairs of small metacentric autosomes. The Xchromosome is a medium­small acrocentric with a slightly visible short second arm; the Y­chromosome is a small acrocentric. This complement is similar to a specimen reported to be of this species from the Rio Jamarí in the Estado do Rondônia, Brazil, which differs only by having three pairs of small metacentric and one fewer pair of acrocentric autosomes, and consequently a fundamental number of 48 instead of 46 (Zanchin et al., 1992) .

SPECIMENS EXAMINED (n = 8): (6) 2m, 1f — JLP 15683, 15704, 15724; (7) 1f — JLP 15426; (9) 1m — JLP 15923; (14) 2m — JUR 417, 438; (15) 1f — JUR 384.