311.

Thomas's Big-toothed

Deermouse

Megadontomys thomasi

French: Peromyscus de Thomas / German: Thomas-Grof 3 zahn-Hirschmaus / Spanish: Raton ciervo de dientes grandes de Thomas

Other common names: Thomas's Deermouse, Thomas's Giant Deer Mouse

Taxonomy. Peromyscus (Megandontomys) thomas: Merriam, 1898, mountains near Chilpancingo, 9700 ft (= 2957 m), Guerrero, Mexico.

Megadontomys thomas: once had three subspecies ( cryophilus, nelsoni, and thomas), but cryophilus and nelsoni were elevated to distinct species. Debate continues as to whether or not Megadontomys is a valid genus or if it should be placed as subgenus of Peromyscus . Monotypic.

Distribution. Known only from the type locality and surrounding regions in Sierra Madre del Sur, C Guerrero, Mexico.

Descriptive notes. Head-body 145-166 mm, tail 150-185 mm, ear 25-28 mm, hindfoot 31-34 mm; weight 62-113 g. Thomas’s Big-toothed Deermouse is large, approaching a medium-sized woodrat ( Neotoma). It is similar in most characteristics to the Oaxacan Big-toothed Deermouse (M. cryophilus) and Nelson’s Big-toothed Deermouse ( M. nelsoni), but there are relatively strong genetic differences among the three species. Thomas's Big-toothed Deermouse most closely resembles Nelson’s Big-toothed Deermouse. Skull is broad, nasals are long, ears are medium-sized, and hindfeet are large. Dorsum is dark brown and thick, sides are deep ocherous-tawny, and venteris creamy white, mixed with slate-colored hairs. Rostrum, cheeks, and orbital region are dark. Feet are white to grizzled on upperparts and dark above ankles. Tail is long and dark. Thomas's Big-toothed Deermouse differs from other species of Megadontomys by being lighter in color and longer and more heavily bodied and by having longer tail and narrower rostral region.

Habitat. Known only from cloud forests and pine ( Pinus, Pinaceae) and oak ( Quercus, Fagaceae) forests, with thickly vegetated areas and dense understories of vines and shrubs, at elevations of 3000-3500 m. It has been captured with the Orizaba Deermouse ( Peromyscus beatae), the Aztec Deermouse ( P aztecus evides), the Broad-faced Deermouse (FP. megalops), the Mexican Woodrat ( Neotoma mexicana), and Alfaro’s Rice Rat ( Oryzomys alfaror).

Food and Feeding. Thomas's Big-toothed Deermouse probably eats seeds.

Breeding. Reproductively active males were captured in April, June-July, and November. Lactating females were recorded in March, May, July, and November. Litters normally have two offspring.

Activity patterns. Thomas’s Big-toothed Deermouse is presumably nocturnal.

Movements, Home range and Social organization. No information.

Status and Conservation. Classified as Endangered on The IUCN Red List. Endemic Thomas's Big-toothed Deermouse has decreasing populations, and is protected by the Federal government of Mexico.

Bibliography. Bradley et al. (2007), Carleton (1989), Musser (1964), Pena & Dominguez (2014b), Platt et al. (2015), Werbitsky & Kilpatrick (1987).