Hyracodon

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Skeletal reconstruction of Hyracodon Hyracodon skeleton, from Abel, O. (1919). Die Stamme der Wirbeltiere.jpg
Skeletal reconstruction of Hyracodon

Hyracodon
Temporal range: Middle Eocene–Late Oligocene
Hyracodon nebraskensis LACM.jpg
Skeleton in Natural History Museum of Los Angeles
Scientific classification OOjs UI icon edit-ltr.svg
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Perissodactyla
Family: Hyracodontidae
Genus: Hyracodon
Leidy, 1856 [1]
Species
  • H. browni
  • H. leidyanus
  • H. medius
  • H. nebraskensis
  • H. petersoni
  • H. affinis
  • H. eximus
  • H. modestus
  • H. primus
  • H. princeps
  • H. priscidens

Hyracodon ('hyrax tooth') is an extinct genus of perissodactyl mammal from the White River Formation.

Contents

Description

It was a lightly built, pony-like mammal of about 1.5 m (5 ft) long. Hyracodon's skull was large in comparison to the rest of the body. Hyracodon's was a much smaller animal than modern Rhinocerotoides and differed very little in appearance from the primitive horses of which it was a contemporary (32–26 million years ago). It had a short, broad snout and its long, slender limbs had three digits. [2] When put next to its comtemporary, Mesohippus , Hyracodon has a proportionally long neck, with robust vertebrae. Compared to earlier hyracodontids from the Uinta Formation, like Triplopus , Hyracodon has more a more gracile manus structure. The median toe is enlarged whilst the lateral toes are greatly reduced. The molars of Hyracodon are similar to those of modern day Rhinoceros, with the last upper molar assuming a triangular shape. The canines and incisors, however were quite different. In form, the anterior teeth of Hyracodon were small and similar in shape, being pointed and curved. [3]

H. nebraskensis skull, found near Hermosa, South Dakota. Hyracodon nebraskensis skull (cropped).jpg
H. nebraskensis skull, found near Hermosa, South Dakota.

Like the primitive horses, hyracodonts inhabited open forests and wooded steppes and turned from browsing foliage to grazing grass. They died out without leaving any descendants and they mark the end of the phylogenetic branch of hornless, running rhinocerotoids.

References

  1. McKenna, M. C; Bell, S. K. (1997). Classification of Mammals above the Species Level. Columbia University Press. ISBN   0-231-11012-X.
  2. Palmer, D., ed. (1999). The Marshall Illustrated Encyclopedia of Dinosaurs and Prehistoric Animals. London: Marshall Editions. pp. 283–284. ISBN   1-84028-152-9.
  3. Scott, William Berryman (1913). A history of land mammals in the western hemisphere. Smithsonian Libraries. New York, The MacMillan Company.

Sources