Thomasomys erro Anthony, 1926

VOSS, ROBERT S., 2003, A New Species of Thomasomys (Rodentia: Muridae) from Eastern Ecuador, with Remarks on Mammalian Diversity and Biogeography in the Cordillera Oriental, American Museum Novitates 3421, pp. 1-48 : 30-32

Thomasomys erro Anthony

Figures 11–13

SPECIMENS COLLECTED: 6.2 km (by road) W Papallacta, 11,700 ft (UMMZ 155711); Río Papallacta valley [3–5 km by trail NNW Papallacta], 11,100 ft (UMMZ 155640– 155642, 155712, 155713); 1.4 km (by road) E Papallacta (AMNH 248283; UMMZ 155633–155639, 155709, 155710); 9 km (by road) E Papallacta, 9280 ft (UMMZ 127133).

OTHER MATERIAL: None.

TAXONOMY: Thomasomys erro was originally described on the basis of a single specimen ( AMNH 68195 ) collected by the Olallas on the ‘‘upper slopes of Mt. Sumaco , exact altitude unknown, but probably 8000– 9000 feet [2440–2740 m], at head of the Río Suno , a tributary of the Río Napo, eastern Ecuador; June 10, 1924 ’’ ( Anthony, 1926: 5). Although only about 50 km SE of Papallacta, Volcán Sumaco (0°34'S, 77°38'W) is an isolated peak that is separated from the main range of the Cordillera Oriental by the lowland valley of the Río Quijos (fig. 14). Populations of montane organisms on the upper slopes of Sumaco are therefore likely to be ecologically disjunct from those in the vicinity of Papallacta.

The Papallacta specimens are the only additional material of Thomasomys erro to have been collected since 1924 and merit close comparison with the holotype ( AMNH 68195 ). No noteworthy differences in pelage color or other external characters are apparent, however. The skull of AMNH 68195 is partially crushed, so only an incomplete set of measurements can be taken, but most of these fall within the range of variation observed among the Papallacta specimens; the exceptions are two molar dimensions in which the type is slightly larger ( table 6). In all qualitative craniodental comparisons, the holotype appears to be indistinguishable from the Papallacta series and appears to represent the same taxon.

Cabrera (1961) listed Thomasomys erro as a subspecies of T. cinereiventer Allen (1912) without explanation, and no discussion of character information has been published to justify the current treatment of erro as a junior synonym of that species (e.g., by Musser and Carleton, 1993). However, side­by­side comparisons of the holotypes and other representative material of erro and cinereiventer do not support the hypothesis that these taxa are conspecific. Among other differences, typical cinereiventer from the Cordillera Occidental of southern Colombia 7 is a much bigger animal with longer hind feet (33–36 mm); deeper zygomatic notches; less inflated interorbital region; more strongly convergent zygomatic arches; more elongate (less globular) braincase; broader and more vertically oriented zygomatic plates; consistently separate buccinator­masticatory and accessory oval foramina; larger (5.7–6.2 mm), incipiently lophodont molars with interpenetrating lingual and labial flexi (see illustrations and discussion of this trait in Voss, 1993); and relatively much broader incisors. Other Colombian taxa that are currently considered to be subspecies or synonyms of T. cinereiventer —including contradictus Anthony (1925) from the Cordillera Central and dispar Anthony (1925) from the Cordillera Oriental—are smaller than the nominotypical form but do not exhibit any other noteworthy similarities with T. erro .

FIELD OBSERVATIONS: I collected 17 specimens of Thomasomys erro in the vicinity of Papallacta , at elevations ranging from 2830 to 3570 m. Of these, 11 were taken in dense secondary vegetation, 5 in Subalpine Rain Forest, and 1 in Upper Montane Rain Forest. All recorded captures were on the ground. Eleven specimens were trapped in runways through wet leaf litter and mossy debris; three were trapped beneath mossy logs, branches, or roots; and one was trapped inside the trunk of a hollow tree .

Figures

Fig. 11. Dorsal cranial views of eight Thomasomys species that occur in the Cordillera Oriental of northern Ecuador. Top row (left to right): T. aureus (UMMZ 127114), T. baeops (UMMZ 155708), T. cinnameus (UMMZ 155671), T. erro (UMMZ 155713). Bottom row (left to right): T. paramorum (UMMZ 155737), T. rhoadsi (AMNH 66256), T. silvestris (USNM 513592), T. ucucha (UMMZ 155644).

Fig. 12. Ventral cranial views of eight Thomasomys species from the Cordillera Oriental of northern Ecuador. Top row (left to right): T. aureus (UMMZ 127114), T. baeops (UMMZ 155708), T. cinnameus (UMMZ 155671), T. erro (UMMZ 155713). Bottom row (left to right): T. paramorum (UMMZ 155737), T. rhoadsi (AMNH 66256), T. silvestris (USNM 513592), T. ucucha (UMMZ 155644).

Fig. 13. Lateral cranial and mandibular views of eight Thomasomys species from the Cordillera Oriental of northern Ecuador. Left side (top to bottom): T. aureus (UMMZ 127114), T. baeops (UMMZ 155708), T. cinnameus (UMMZ 155671), T. erro (UMMZ 155713). Right column (top to bottom): T. paramorum (UMMZ 155737), T. rhoadsi (AMNH 66256), T. silvestris (USNM 513592), T. ucucha (UMMZ 155644).