Trigonias (Greek: "triangular" (trigonos), "ias" [denotes possession]) is an extinct genus of rhinocerotid from the late Eocene (Chadronian) some 35 million years ago of North America.
Trigonias was about long and, despite lacking horns, looked a lot like modern rhinos. The front feet bore 4 toes (as contrasted with three in modern rhinos), the fifth of which was entirely reduced. The median digit was already the largest, whilst the second and the fourth formed a symmetrical pair. The hind feet had only 3 digits.
The shape of the anterior incisors in the upper jaw of Trigonias assume a chisel-like shape. The other 2 incisors are less derived. Trigonias also bore a reduced upper canine, unlike most rhinocerotids. In the lower jaw, the second incisor grew large and tusk-like, and there was no canine. Trigonias also had small premolars when compared to the molars. The dental formula of Triognias was .
A specimen of T. osborni was estimated to have a weight of about .
Cladogram after Lu, Deng and Pandolfi, 2023: