Dactylomys boliviensis Anthony, 1920

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 : 173-176

Dactylomys boliviensis Anthony, 1920

TYPE LOCALITY: ‘‘ Mission San Antonio Rio Chmore [sic, Chimore´], Prov. Cochabamba, Bolivia ; altitude 1300 feet.’’

DESCRIPTION: This is a large rat, with more muted dorsal color tones and a proportionately longer tail than D. dactylinus (table 48) The mystacial vibrissae are short, extending only to one half the length of the superciliary vibrissae, in contrast to the much longer mystacial vibrissae of D. dactylinus (fig. 116 The face is distinctly gray above and below the eyes with an olivaceous black stripe bordered by pale tipped hairs extending on the midline from the nose posteriorly between the ears to the nape, darkening progressively to blackish brown from above the eyes to the neck (fig. 116). The dorsal body color is grizzled grayish­olivaceous streaked with black becoming paler on the sides, and gradually merging with the sparsely furred, pure white venter. There is only a slight hint of orange on the inside of the thighs. Individual hairs of the middorsum are of two types: somewhat heavier and longer hairs that are tricolored, with an elongated basal black band, a narrow subterminal pale yellow one, and a black tip; and shorter, thinner, and more common totally black hairs. As a result, if one parts the hair the undercolor is black to the skin. This color pattern contrasts sharply with specimens of D. dactylinus , as noted in the account of that species below. The tail has a well­furred base that extends for about 65 mm; it is heavily scaled and naked in appearance from furred base to tip, but the scales appear finer, averaging six annuli per cm near the tail base and 7.5 per cm near the tip, and less distinctly pentagonal than those of D. dactylinus . Each caudal scale­hair is distinctly dark brown or black over the basal half, becoming completely colorless along the terminal half to third of the tail. The median hair extends 1.5 to 2 scale rows. The tail is also distinctly bicolored, especially over the anterior two thirds of its length, but with the broad and dark dorsal stripe becoming gradually paler towards the tip.

The skull is large, with a short rostrum and broad, well­developed supraorbital ledges that form sub­triangular supraorbital processes (fig. 113). The few specimens of D. bo­ liviensis we examined differ from all individuals in a larger series of D. dactylinus by having anteriorly directed paroccipital processes that follow the curvature of the auditory bulla, and having a postorbital process of the zygomatic arch comprised primarily of the jugal. The upper toothrows diverge strongly posteriorly, with left and right PM4 nearly meeting at the midline. The individual teeth exhibit coronal hypsodonty, have welldeveloped roots, and a planar occlusal surface. Each consists of four transverse lophs, with both an anterior and posterior pair separated by a deep median flexus but joined lingually and thus form a distinctive Y shape; the two pairs of lophs are separated by a transverse flexus that extends completely across the tooth (fig. 114, left). Both the individual lophs and lingual confluence appear narrower, and with sharper corners, in D. boliviensis than in D. dactylinus , although this is partly due to differences in absolute wear between the specimens available to us for comparison (fig. 114).

SELECTED MEASUREMENTS: We list external and cranial measurements of one individual in table 48.

DISTRIBUTION AND HABITAT: Individuals were observed, collected, or detected by their odor only in the dense and extensive bamboo thickets at Igarapé Porongaba (locality 1) or at the community of Flora (locality a) in the headwaters of the Rio Jurua´. These, and all other individuals heard along the river above Cruzeiro do Sul in Estado do Acre exhibited the same vocal structure with a staccato series of short pulses, ranging from about 15 to 45 and averaging around 20 (based on counts made by ear, not by recordings).

REPRODUCTION: All specimens were collected in the month of February; neither sex exhibited any indication of reproductive activity although the vagina of the single female was perforate.

COMMENTS: As noted by da Silva and Patton (1993), the call structure of the vocalizations of this animal differs markedly from that of D. dactylinus heard in middle and lower reaches of the Rio Jurua´. The latter expressed no more than five to 10 individual pulses in a given vocalization, with an average of about seven. Call structure varies extensively throughout Amazonia (Emmons, 1981; Emmons and Feer, 1997), but is organized geographically into high or low pulse numbers that likely correspond to the two species we recognize here (P. Santos, J. Podos, and M. N. F. da Silva, unpubl. data). The two species likely encounter one another somewhere along the upper Rio Juruá between our Upper Central sampling sites and Cruzeiro do Sul (fig. 1). We did not travel this section of the river, and thus have no notes on the nature of vocalizations through this area.

SPECIMENS EXAMINED (n = 3): (a) 2m, 1f (MNFS 988, 1005, 1105).