Dinocerata, from Ancient Greek δεινός (), "terrible", and κέρας (), "horn", or Uintatheria,[Blackwelder, R. E. Classification of the Animal Kingdom. Carbondale: Southern Illinois University Press. 1963. p. 71] is an extinct order of large herbivorous hoofed mammals with horns and protuberant canine teeth, known from the Paleocene and Eocene of Asia and North America. With body masses ranging up to they represent some of the earliest known large mammals.[Spencer G. Lucas, Robert M. Schoch 19. "Dinocerata" in: Evolution of Tertiary Mammals of North America: Volume 1, Terrestrial Carnivores, Ungulates, and Ungulate like Mammals (1998)]
Description
Uintatheriids are suggested to have been browsers. Over the course of their evolution, dinoceratans underwent a great increase in body size, from a weight of in the earliest species to a weight of up to 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
and
Parietal bone 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.
Evolution
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 (probably via
Beringia), with uintatheres continuing to exchange between the landmasses during the Eocene, as suggested by the presence of
Uintatherium in both North America and China. Uintatheres became extinct towards the end of the Middle Eocene, for unknown reasons.
Classification
The affinities of the group within
Placentalia have historically been contentious. A 2015 phylogenetic study recovered Dinocerata as part of
Laurasiatheria, closely related to
and "
", with Dinocerata placed as the sister group to the South American native ungulate group
Xenungulata.
A close relationship with Xenungulata was first proposed in 1985, with the proposed clade containing both groups named Uintatheriamorpha,
though other authors have suggested that these similarities are likely to be due to convergence.
Taxonomy and phylogeny
Dinocerata is generally divided into two families, "Prodinoceratidae", containing the most primitive genus
Prodinoceras, with some authors also choosing to include the genus
Probathyopsis and Uintatheriidae, containing all other genera. Members of Prodinoceratidae are likely ancestral to Uintatheriidae.
The Asian uintatheriid genus
Gobiatherium is often placed into its own separate subfamily Gobiatheriinae, with all other uintatheriids belonging to the subfamily Uintatheriinae.
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Order Dinocerata
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Family Prodinoceratidae
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Family Uintatheriidae
