The fossil record of Megatheriinae (Tardigrada, Megatheriidae) in Argentina extends from the Colloncuran (Middle Miocene of Patagonia) to the Lujanian (Late Pleistocene—Early Holocene of the Pampean region). In the Late Miocene of north-western Argentina, Megatheriinae is represented by just three species belonging to a single genus, Pyramiodontherium. Here, we describe a partial mandible and the phalanges of a third digit of the manus recovered from the Saladillo Formation (Upper Miocene) of Tucumán Province, and assign them to Anisodontherium sp. Anisodontherium is primarily characterized by mesiodistally compressed molariforms, an anterior margin of the coronoid process located posterior to m4, and a posterior margin of the mandibular symphysis located anterior to m1. While these features can also be observed in A. halmyronomum from the Arroyo Chasicó Formation (Buenos Aires Province, Pampean region), Anisodontherium sp. is smaller and more slender than the former. The shape of each molariform of Anisodontherium affects the total length of the molariform tooth row, and thus the interpretation of some characters used in cladistic and paleobiological analyses. The material described here adds to the knowledge of the mandibular and dental anatomy of early megatheriines. In addition, the occurrence of Anisodotherium in Tucumán Province provides the first record of this genus outside the Pampean region, and increases the diversity of megatheriines during the Late Miocene—Pliocene of north-western Argentina.