Thomas's Big-toothed Deermouse shares its genus and unusually large teeth with two other giant rodent species endemic to the Mexican mountains. It differs from them by inhabiting a distinct mountain massif in southern Oaxaca, neatly illustrating how a single rodent lineage has fragmented into separate species as the different mountain ranges became isolated from one another. It lives in cloud forest and mid- to high-elevation pine forest, moving along the understorey floor in search of seeds, fruit and invertebrates. Its name honours the British zoologist who first described numerous Mesoamerican mammal species in the late 19th and early 20th centuries. It is one of several endemic rodent species in Oaxaca whose survival depends on preserving the region's already restricted mountain forest.
A large rodent for a Mesoamerican murid, with dark brown fur, large ears, and teeth notably well developed in proportion to the skull. Thomas's Big-toothed Deermouse differs from other species in its genus by its range in southern Oaxaca, with no geographical overlap with sister species in Veracruz and other areas of Oaxaca.
Tracks and signs include tracks with 4 fore toes and 5 hind toes, the hind track 2-2.5 cm long. Elongated droppings 8-10 mm long, left scattered along surface runways beneath dense understorey vegetation. It builds grass and moss nests in hollows beneath fallen logs or roots in the damp soil of the cloud and mountain pine forests it inhabits.
Cloud forest and mid- to high-elevation mountain pine forest with dense understorey, generally between 2000 and 3000 m altitude. Endemic to an area of the southern Sierra Madre de Oaxaca in southern Mexico.
Omnivorous, feeding on seeds, fruit, fungi and invertebrates from the mountain forest floor.
Terrestrial, with solitary and territorial behaviour. It is probably nocturnal, like the other rodents in its genus.
Populations are considered to be in decline due to the ongoing loss of the cloud forest and mountain pine forest on which Thomas's Big-toothed Deermouse depends, an already restricted mountain ecosystem in the southern Sierra Madre de Oaxaca.
Deforestation and fragmentation of mountain forest caused by agricultural and livestock expansion in southern Oaxaca.
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