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Temporal range: 35–5 Ma
Late Eocene
Scientific classification e
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Artiodactyla
Family: Merycoidodontidae
Subfamily: Aclistomycterinae
Lander 1998
Genus: Aclistomycter
Wilson 1970
  • Aclistomycter middletoni Wilson 1970

Aclistomycter is an extinct genus of oreodont during the early Chadronian subepoch (42—39.9 mya, Late Eocene) existing for approximately 2.1 million years [1] from the Chambers Tuff Formation near Adobe Springs in Presidio County, Texas.

Aclistomycter was a very small herbivorous artiodactyl with a short face, small, but tusk-like canine teeth. The type specimen (TMM 41213-1) consists of a skull and jaws and two other specimens are referred to it: TMM 41216-11, skull with C-M^3; TMM 41211-9, skull fragment with M^1-M^3.


Generic characters assigned by Wilson (1970):

  • Medium small merycoidodontid with very large and deep, probably perforated, antorbital fossae.
  • Brachycephalic.
  • Posterior part of skull extended.
  • Molar teeth with thick enamel and deep fossettes.
  • Posterior base of zygomatic processes wide, making the skull broad posteriorly.
  • Bullae thought to be inflated (though the bullae are not exposed in the figures of the type specimen illustrated by Wilson).


Aclistomycter was named and assigned to Merycoidodontidae and the Merycoidodontinae by Wilson (1971). But Lander (1998) erected a new subfamily for it, the Aclistomycterinae. [2][3] Wilson recognized it was more primitive than Leptauchenia and Lander placed it as more derived than the bathygenines but basal to leptaucheniines and other more derived merycoidodontids.


A single specimen was examined by M. Mendoza for body mass and estimated to have a weight of 87.9 kg (193.7 lbs). [4]


  1. ^ PaleoBiology Database: Aclistomycter, basic info
  2. ^ J. A. Wilson. 1971. Early Tertiary vertebrate faunas, Vieja Group. Trans-Pecos Texas: Agriochoeridae and Merycoidodontidae. Texas Memorial Museum Bulletin
  3. ^ B. Lander. 1998. Oreodontoidea. In C. M. Janis, K. M. Scott, and L. L. Jacobs (eds.), Evolution of Tertiary mammals of North America 402-425
  4. ^ M. Mendoza, C. M. Janis, and P. Palmqvist. 2006. Estimating the body mass of extinct ungulates: a study on the use of multiple regression. Journal of Zoology