Thomasomys cinnameus Anthony, 1924

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 : 29-30

Thomasomys cinnameus Anthony

Figures 11–13

SPECIMENS COLLECTED: 1.6 km (by road) W Papallacta, 10,500 ft (UMMZ 155668– 155670); Río Papallacta valley [3–5 km by trail NNW Papallacta], 11,100 ft (AMNH 155671, 155800).

OTHER MATERIAL: None.

TAXONOMY: This material of Thomasomys cinnameus was the first to be reported (by Voss, 1988: table 43) since the original description based on a single specimen collected at 8000 ft (2438 m) near Hacienda San Francisco, Provincia Tunguragua, Ecuador ( Anthony, 1924b). Side­by­side comparisons indicate that the Papallacta series closely resembles the holotype (AMNH 67401) in all qualitative and most quantitative characters. Although the holotype slightly exceeds the Papallacta specimens in several external and craniodental measurements ( table 5), the differences are so small and the number of Papallacta specimens (five) is so few that these discrepancies do not seem taxonomically significant.

One of the smallest known species of the genus, Thomasomys cinnameus is currently regarded as a subspecies or junior synonym of T. gracilis Thomas (1917) , originally described from a specimen collected at Machu Picchu in southern Peru ( Cabrera, 1961; Musser and Carleton, 1993). However, the hypothesis that cinnameus and gracilis (with type localities separated by 1500 km of highly dissected mountainous terrain) are conspecific is unsupported by any published analysis or discussion of character data. Rather, my examination of both holotypes and other representative material 6 indicates that these are unambiguously diagnosable taxa that should be recognized as distinct species.

Although similar to Thomasomys gracilis in size, external proportions, and pelage coloration, T. cinnameus consistently lacks genal vibrissae, long black tactile hairs of the upper cheek that are consistently present in gracilis . Among other trenchant craniodental comparisons, cinnameus is distinguished by (1) incisive foramina that are widest posteriorly, behind the maxillary/premaxillary suture; (2) absence of sphenopalatine vacuities; (3) smaller and less inflated auditory bullae; and (4) larger and more hypsodont molars with weakly developed cingula and stylar cusps. By contrast, gracilis exhibits (1) incisive foramina that are widest anteriorly, at or near the maxillary/premaxillary suture; (2) large sphenopalatine vacuities that perforate the bony roof of the mesopterygoid fossa on each side of the basisphenoid/presphenoid suture; (3) larger and more inflated auditory bullae; and (4) smaller, brachydont molars with better developed cingula and stylar cusps.

Thomasomys hudsoni Anthony (1923) is another small Ecuadorean taxon that has been treated without explanation as a synonym or subspecies of T. gracilis (see Cabrera, 1961; Musser and Carleton, 1993). However, I agree with Anthony (1924b) that hudsoni is a distinct species, differing from both gracilis and cinnameus in details of coloration and craniodental morphology. Unlike any specimens of the other small species, the type of hudsoni (AMNH 47690, from Bestión in Provincia Azuay) has a rostrum that is peculiarly produced beyond the incisors as a flaring bony tube with a concave (rather than convex) dorsal profile. As in cinnameus (and unlike gracilis ) genal vibrissae and sphenopalatine vacuities are absent in hudsoni , but as in gracilis (and unlike cinnameus ) the incisive foramina are widest anteriorly (near the maxillary/premaxillary suture). The auditory bullae of hudsoni are larger and more inflated than those of cinnameus but smaller and less inflated than those of gracilis . Unfortunately, the molars of the type (and only known specimen) of hudsoni are too worn to support confident dental comparisons.

FIELD OBSERVATIONS: The five specimens of Thomasomys cinnameus that I collected near Papallacta in 1980 were trapped at elevations ranging from 3200 to 3380 m. Of these, three were taken among mossy boulders in an old lava flow that impounds the Río Tambo to form Laguna Papallacta (fig. 1), and two were trapped on the ground in Subalpine Rain Forest in the valley of the Río Papallacta 3–5 km (by trail) NNW of the town .

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).