Trigonias

This article is about the extinct rhinoceros. For the bivalves, see Trigoniidae.

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 Temporal range: late Eocene[1]
T. osborni
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Order:	Perissodactyla
Family:	Rhinocerotidae
Genus:	†Trigonias Lucas, 1900
Type species
†Trigonias osborni
Species[2]
†T. osborni †T. wellsi
Synonyms
†Procaenopus Figgins, 1934[2]

Description

Trigonias was about 2.1 metres (6 ft 11 in) 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.^[5] The median digit was already the largest, whilst the second and the fourth formed a symmetrical pair. The hind feet had only 3 digits. ^[6]

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 3,1,4,33,0,4,3 × 2 = 42.^[6]

A specimen of T. osborni was estimated to have a weight of about 391 kilograms (862 lb).^[7]

Cladogram after Lu, Deng and Pandolfi, 2023:^[8]

Rhinocerotidae	Trigonias Ronzotherium Epiaceratherium Diceratherium Molassitherium Skinneroceras Aceratheriinae (including Teleoceratini) Protaceratherium Menoceras Rhinocerotinae (modern rhinoceroses) Elasmotheriinae