One of the least documented Mexican rodents of all: it is known with certainty from just a single hill in Oaxaca, and it is not even clear whether it still exists, as no confirmed specimen has been trapped for decades despite several search attempts. Its scientific name, meaning delicate in Latin, refers to its slender, dainty body, smaller than that of most of its close relatives within the same genus of Mesoamerican climbing mice. It inhabited the cloud forest and mountain pine-oak forest of a very specific massif, a habitat that has undergone considerable transformation since the last definitively known specimens were collected. Its status, midway between confirmed extinction and a simple lack of recent surveys, makes it a case study in how poorly explored the small mammal fauna of the Mexican mountains remains.
Small rodent with a more graceful build than other species in its genus, greyish-brown fur, large eyes, well-developed ears and a long, prehensile tail. Confused with other species of tree mice in the mountains of Oaxaca, from which reliable separation requires genetic or cranial analysis; its origin from a single known hill is the most useful clue to guide identification.
Small track, 1.3-1.8 cm, with 4 foretoes and 5 hind toes, rarely visible given its climbing habits. Small, elongated droppings 3-5 mm long, left scattered through low vegetation and raised leaf litter. Builds spherical nests of grass and moss among dense vegetation or in tree hollows above ground level, although no recent confirmed records exist to document these tracks and signs with certainty.
Cloud forest and mountain pine-oak forest with dense understorey, generally above 2500 m altitude. Known from a single hill in the Sierra Madre de Oaxaca in southern Mexico, with no confirmed records outside that locality.
Omnivorous, presumably feeding on seeds, fruit, fungi and understorey invertebrates like other species in its genus, although no direct data exists on its specific diet.
Arboreal and climbing in habit, like the rest of its genus, with solitary and probably nocturnal behaviour; its detailed biology is virtually unknown given the absence of recent confirmed records.
No recent record of the species has been confirmed in recent decades despite several search attempts, and the transformation of the mountain forest at its only known locality raises fears that, if it survives, it does so in an extremely reduced population.
Deforestation and transformation of the cloud and pine-oak forest at its only known locality, combined with the extreme geographical restriction of the species, which is limited to a single hill.
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