Dinocerata

Skull of Prodinoceras, one of the earliest dinoceratan genera

Over the course of their evolution, dinoceratans underwent a great increase in body size, from a weight of 175 kilograms (386 lb) in the earliest species to a weight of up to 4,500 kilograms (9,900 lb) in the largest species, co-inciding with the development of fully graviportal limbs with a digitigrade posture. Later members of the order are noted for their distinctive pairs of horns that develop from the maxillary and parietal bones of the skull, along with the development of elongated upper canines. The upper incisors were also lost, and the bilophodont nature of the molar teeth was enhanced.[1]

Uintatheriids are suggested to have been browsers.[1]

The oldest and most primitive members of the group, such as Prodinoceras, appeared virtually simultaneously during the late Paleocene in North America and Asia, indicating connection between the two landmasses, with uintatheres contiuing to exchange between the landmasses during the Eocene, as suggested by the presence of Uintatherium in both North America and China. Uinatheres became extinct towards the end of the Middle Eocene, for unknown reasons.[1]

The affinities of the group within Placentalia have historically been contentious. A 2015 phylogenetic study recovered Dinocerata as part of Laurasiatheria, closely related to ungulates and "condylarths", with Dinocerata placed as the sister group to the South American native ungulate group Xenungulata.[2] A close relationship with Xenungulata was first proposed in 1985, with the proposed clade containing both groups named Uintatheriamorpha,[1] though other authors have suggested that these similarities are likely to be due to convergence.[3]

Dinocerata is generally divided into two families, "Prodinoceratidae", containing the most primitive genus Prodinoceras,[1] with some authors also choosing to include the genus Probathyopsis[4], and Uintatheriidae, containing all other genera. Members of Prodinoceratidae are likely ancestral to Uintatheriidae.[1] The Asian uintatheriid genus Gobiatherium is often placed into its own separate subfamily Gobiatheriinae, with all other uintatheriids belonging to the subfamily Uintatheriinae.[5]

• Order Dinocerata
  • Family Prodinoceratidae
    • Prodinoceras
    • ?Probathyopsis[4]
  • Family Uintatheriidae
    • Gobiatherium
    • Probathyopsis
    • Bathyopsis
    • Uintatherium
    • Eobasileus
    • Tetheopsis