Urtinotherium was a representative of the large family Paraceratheriidae, and almost reached the proportions of Paraceratherium. It is known from several findings in central and eastern Asia, though no complete skeletons are known. The holotype fossil (catalog number IVPP V.2769) includes a complete lower jaw 71.5 cm (28.1 in) in length, comparable to the smallest known of Paraceratherium. The jaw is wedge shaped, very low in height, and with elongated branches. The symphysis was solid and extended to the beginning of the second premolars. The jaw's dentition is complete, having three front incisors and canine. The first two incisors protrude forward with a crown length of 4.9 cm (1.9 in), with forms similar to daggers. The other incisors and canines had much smaller crowns. Between each tooth is a small space, similar to its phylogenetically primitive relatives such as Juxia. Its back teeth, which are separated from the front teeth by a small diastema, consist of four premolars and three molars. These are similar in structure to those of Paraceratherium, with small premolars and larger molars. The latter have low crowns (are brachyodont) and had few enamel folds.[3]
Urtinotherium pertains to the Paraceratheriidae subfamily Paraceratheriinae. These in turn are part of the superfamily Rhinocerotoidea and therefore represent close relatives of modern rhinoceroses. The paraceratheres are distinguished by the formation of large sharp incisors in their upper and lower jaws, while rhinoceroses only have a two on the lower jaw. Urtinotherium was thought of by Leonard Radinsky to be a transitional form between earlier paraceratheres, like Juxia, and later forms, such as Paraceratherium and Indricotherium (now Paraceratherium transouralicum).[5]
This genus represents a primitive form of paracerathere that developed in the late Eocene. It is possibly descended from Juxia, which lived during the Middle Eocene in northern China, and which shares with it having a full set of teeth in its jaws. However, Urtinotherium differs by its larger body size and greater specialization in the incisors.[6]Urtinotherium and later Paraceratherium form the most derived section of the largest known rhinocerotoid lineage. In their specialization emphasizes that compared to Urtinotherium, they possessed significantly reduced dentition with only a couple of incisors in the lower jaw.[7]
The first description of Urtinotherium was published in 1963 by Zhou Ming-Zhen and Chiu Chan-Siang, based on the lower jaw. The type species is recognized as Urtinotherium incisivum. The genus name comes from the location, and from the Ancient Greek word θηρίον (therion) meaning "beast". The species name refers to its elongated incisivos.[3]
^Radinsky, L.B. (1966). "The families of the Rhinocerotoidea (Mammalia, Perissodactyla)". Journal of Mammalogy. 47 (4): 631–639. doi:10.2307/1377893. JSTOR1377893.