Thomas's Big-eared Brown Bat is a medium-sized bat with large ears. It is recorded in Argentina’s Yungas forests, eats insects, and roosts in buildings or natural caves.
Its fur is soft and dense, with dark brown upperparts. The belly hairs are dark at the base and yellowish at the tips. Large ears are joined by a band of skin across the forehead.
It feeds on insects and uses both buildings and natural caves as roosts, including in Yungas forest landscapes.
The flight membranes are pale grey or brown and slightly translucent. The membrane around the tail is almost hairless, with a long, slender calcar supporting it.
In Argentina, it is a medium-sized bat with a forearm length of 45–49 mm.
An extinction-risk assessment has not been added yet.