Dactylomys dactylinus (Desmarest, 1817)

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 : 176-178

Dactylomys dactylinus (Desmarest, 1817)

TYPE LOCALITY: No locality given in original description, but presumed to be eastern

Peru´; restricted to ‘‘ Upper Amazon area’ (Thomas, 1912: 88). However, this restriction is likely to be in error, as most specimens from Amazonia in the Muséum d’Histoire Naturelle in Paris, where Desmarest’s type is housed, are probably from central Brazil, the lower Amazon, or French Guiana (R. S Voss, personal commun.) .

DESCRIPTION: This taxon is similar to D boliviensis , described above, but clearly differs in several features. Among our specimens, this taxon is absolutely larger in most cranial dimensions, but has a shorter tail relative to head and body length (table 48). The face is pale tan above and below the eyes nose, and over the rostrum, gradually darkening to chestnut between the ears and posteriorly onto the neck (fig. 116). This stripe is never blackish­brown, as in D. boliviensis and it contrasts sharply with the grizzled yellowish dorsum, which is streaked with black hairs. The dorsal hairs are chestnut at their bases, with a subterminal black band and yellow or pale yellow tips. The sides become progressively more fulvous, with the thighs distinctly burnt orange. There is a white band encircling the ankle. The middorsal hairs are also of two types, but these contrast sharply in color pattern compared to D. boliviensis The heavier and longer hairs are bicolored black basally with a short pale yellow tip; the more abundant thinner hairs are reddish basally with short dark tips. As a result, the parted hair appears distinctly dull reddish to the skin, with a mixture of black streaks. As in D. boliviensis , the venter is sparsely covered with completely white hairs. The base of the tail is fully haired for about 60 mm then appearing naked to the tip. The scales are large, prominent, more pentagonal and coarser in appearance than in D. boliviensis and average about five annuli per cm near the base or six per cm at the tip. The scale hairs appear correspondingly shorter, extending less than 1.5 scale rows. All scale hairs are completely colorless along the entire length of the tail distal to its furred base.

The general cranial conformation is the same as described above for D. boliviensis as are the rooted but hypsodont and strongly diverging cheek toothrows (fig. 113). As not­ ed, however, the transverse lophs of D. dac­

tylinus appear broader and rounded (fig. 114, right), although caution must be taken to compare individuals of equivalent toothwear. While the skull of D. dactylinus is larger in almost all dimensions, our comparisons are limited to just two specimens, each with different levels of toothwear and, thus, presumptive age. Further details of cranial morphology must await comparisons of adequate series of specimens. However, all specimens of D. dactylinus we have examined (those from the Rio Jurua´, the Rio Jaú, and from along the Rio Solimões from northeastern Perú to below Manaus have more vertically oriented paroccipital processes that do not follow the contour of the auditory bulla.

SELECTED MEASUREMENTS: See table 48.

DISTRIBUTION AND HABITAT: We collected our two specimens in bamboo and cane thickets on the margins of várzea and terra firme forest.

REPRODUCTION: The single female was pregnant with two fetuses, each measuring 97 mm from crown to rump. The male had enlarged testes and was presumably reproductively active. Both were caught in June, during the high­water season.

COMMENTS: All individual D. dactylinus heard throughout the lower and middle sections of the Rio Juruá produced vocalizations with a range from 5 to 10 pulses, with a mean of 7 (see da Silva and Patton, 1993; P. Santos, J. Podos, and M. N. F. da Silva, unpubl. data). This call structure contrasts sharply with that described above for D. boliviensis . Emmons and Feer (1997: 244) suggest that the head patch of museum specimens may bleach severely with age, thus accounting for the range in color from ‘‘almost white to brown or tan and black sometimes with a rusty stripe.’’ However, the differences in head stripe we describe here for D. dactylinus as opposed to D. boliviensis were evident in freshly collected specimens from these, and other, localities, and the blackishbrown patch of our specimens of D. boliviensis has not bleached in the nearly six years since they were collected, including specimens that were preserved in formalin and have been maintained in 70% ethanol.

SPECIMENS EXAMINED (n = 2): (14) 1m, 1f (JUR 485, MNFS 1736).