Trachytherus is an extinct genus of mesotheriid notoungulate that lived from the Late Oligocene to the Early Miocene in what is now South America.

The most notable difference between the two genera was in the zygomatic arch; in the anterior region, the insertion surface of the lateral masseter was highly developed, but not as large than in Mesotherium.

The first upper incisor was highly developed, continuously growing (hypsodont) and arched, with an enamel band only on the labial side.

Several other species have been assigned to Trachytherus, such as T. medocensis, T. ramirezi, T. alloxus, T. subandinus, T. modestus, T. grandis, found in Bolivia, Peru, and Argentina.

[1] Though at times considered a grazer, Trachytherus had a complex dietary habit that was not exclusively or predominantly based on grasses.