Trigonias (Greek: "triangular" (trigonos), "ias" [denotes possession][3]) is an extinct genus of rhinocerotid from the late Eocene (Chadronian) some 35 million years ago of North America.

[4] Trigonias was about 2.1 metres (6 ft 11 in) long and, despite lacking horns, looked a lot like modern rhinos.

Its front legs had five toes (as contrasted with three in modern rhinos), the fifth of which was vestigial.

[5] A specimen of T. osborni was estimated to have a weight of about 391 kilograms (862 lb).

Cladogram after Lu, Deng and Pandolfi, 2023:[7]Trigonias Ronzotherium Epiaceratherium Diceratherium Molassitherium Skinneroceras Aceratheriinae (including Teleoceratini) Protaceratherium Menoceras Rhinocerotinae (modern rhinoceroses) Elasmotheriinae