Thomasomys aureus (Tomes)

Figures 11–13

SPECIMENS COLLECTED: 6.2 km (by road) W Papallacta, 11,700 ft (AMNH 248281, 248498; UMMZ 127114, 155621–155624, 155626, 155707); Río Papallacta valley [3– 5 km by trail NNW Papallacta], 11,100 ft (UMMZ 155625).

OTHER MATERIAL: None.

TAXONOMY: The holotype of Thomasomys aureus (BMNH 7.1.1.104) consists of the skin only of a specimen collected by Louis Fraser, allegedly at Pallatanga (1°59'S, 78°57'W; 1500 m above sea level) in the Ecuadorean province of Chimborazo (Allen, 1914; Ellerman, 1941; Cabrera, 1961), or at Gualaquiza (3°24'S, 78°33'W; 971 m above sea level) in the Ecuadorean province of Morona­Santiago (Thomas, 1920). Neither locality, however, is within the usual altitudinal range of this species (ca. 3000–4000 m), and the exact provenance of Fraser’s Ecuadorean material is uncertain due to inadequate labelling and the lack of detailed field records (Gardner, 1983). Despite the absence of cranial material and a definite geographic datum, however, the type serves to establish that aureus is a distinctively large, shaggy rat with grizzled yellowish­brown dorsal fur; yellow­washed, gray­based ventral fur; long, blackish mystacial vibrissae; dark, broad hind feet with semiopposable fifth digits; and a tail that is much longer than the combined length of head­and­body. Other Ecuadorean specimens with these external characters exhibit the qualitative craniodental characters listed in table 2 and approximate the range of morphometric variation summarized in table 3.

Among the several nominal taxa currently synonymized with Thomasomys aureus by Musser and Carleton (1993), the same qualitative and morphometric traits are shared by princeps Thomas (1895a) from the eastern Andes of Colombia and by altorum Allen (1914) from the western Andes of Ecuador. Other putatively synonymous taxa, however, differ conspicuously from aureus in side­byside morphological comparisons: popayanus Allen (1912) from the western Andes of Colombia and nicefori Thomas (1921) from the Colombian central Andes have substantially shorter (33–34 mm) hind feet and smaller (6.0 –6.6 mm) molar toothrows, whereas praetor Thomas (1900) from northern Peru has grayish dorsal fur, pale­silvery ventral fur, pale hind feet, shorter tail, narrower interorbit, and a broad, distinctively flattened braincase. These three taxa were first treated as conspecific with T. aureus by Cabrera (1961), who (as usual) offered no explanation for his nomenclatural changes. In view of such trenchant character differences, at least four species appear to be represented in this complex: T. aureus (including altorum and princeps), T. praetor, and T. popayanus (possibly including nicefori).

FIELD OBSERVATIONS: The 10 specimens of Thomasomys aureus that I collected near Papallacta in 1978 and 1980 were all taken in Subalpine Rain Forest at elevations ranging from 3380 to 3570 m. Six were trapped in well­worn paths through mats of moss and liverworts on horizontal tree limbs, and four were trapped on the ground. Of the latter, two were trapped at the edge of a stream, one was trapped among tall grass in a clearing, and one was trapped in a runway through dense mats of moss.