Dinohippus

Dinohippus Temporal range: Late Miocene–Late Pliocene PreЄ Є O S D C P T J K Pg N
Dinohippus leidyanus skeleton
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Order:	Perissodactyla
Family:	Equidae
Subfamily:	Equinae
Tribe:	Equini
Genus:	†Dinohippus Quinn, 1955
Species
Dinohippus interpolatus Dinohippus mexicanus Dinohippus spectans Dinohippus leardi Dinohippus leidyanus

Dinohippus (Greek: Terrible horse) is an extinct herbivorous mammal belonging to the tribe Equini, subfamily Equinae, which was endemic to North America from the late Hemphillian stage of the Miocene through the Zanclean stage of the Pliocene (10.3—3.6 mya) and in existence for approximately 6.7 million years.^[1][2]

Taxonomy

Skull

Dinohippus was named by Quinn in 1955^[3] and assigned to Equidae by Quinn that same year, by B. J. MacFadden (1986)^[4] and R. L. Carroll (1988);^[5] and to Equini by MacFadden.

It was the most common horse in North America and like Equus, Dinohippus did not have a dished face. It has a distinctive passive "stay apparatus," formed by bones and tendons, to help it conserve energy while standing for long periods. Dinohippus is the first horse to show a rudimentary form of this character, providing additional evidence of the close relationship between Dinohippus and Equus.^[6] Dinohippus was originally thought to be a monodactyl horse, but a 1981 fossil find in Nebraska shows that some were tridactyl.^[7]

Morphology

Three specimens were examined for body mass by M. Mendoza, C. M. Janis, and P. Palmqvist as well as M. T. Alberdi, J. L. Prado, and E. Ortiz-Jaureguizar.^[8][9]

• Specimen 1: 567.7 kg (1251 lbs)
• Specimen 2: 536.5 kg (1182.7 lbs)
• Specimen 3: 224.0 kg (493.8 lbs)

Fossil distribution

Fossil distribution is widespread throughout North America with more than 30 sites from Florida to Alberta, Canada to Central Mexico.

Species

Dinohippus interpolatus

Foot bones

Dinohippus interpolatus (synonymized with Pliohippus bakeri), D. leardi, D. leidyanus (syn. Pliohippus edensis, Pliohippus osborni)

• Taxonomy: Hippidium interpolatum was named by Cope (1893) and said originally to have been placed in. Its type locality is Goodnight Bed Formation. Hippidium interpolatum was a grazing and browsing animal.
• Morphology: One specimen was examined by M. Mendoza, C. M. Janis, and P. Palmqvist. The body mass was estimated to be 119.7 kg (263.8 lbs).^[10]

Mendoza et al. (2006:99) state that D. leidyanus body mass ~200 kg.

Dinohippus mexicanus

Dinohippus mexicanus (synonymized with Equus mesamexicanus, Hippotigris ocotensis, Protohippus muelleri),

• Taxonomy: was named by Lance in 1950 and recombined as Asinus mexicanus by Quinn (1955); it was recombined as Dinohippus mexicanus by May and Repenning (1982), MacFadden (1984), MacFadden (1986) and Kelly (1998).^[11][12]
• Morphology: One specimen was examined by M. Mendoza, C. M. Janis, and P. Palmqvist. The body mass was estimated to be 259.7 kg (572.5 lbs).^[13]

Dinohippus spectans

Dinohippus spectans (synonymized with Equus mesamexicanus, Hippotigris ocotensis, Protohippus muelleri),

• Taxonomy: was named by Cope in 1880, Zittel (1893), Roger (1896), Matthew (1899), Trouessart (1905), Merriam and Sinclair (1907), Cope and Matthew (1915), Osborn (1918), Merriam and et al. (1925), Hay (1930), Stirton (1940), Quinn (1955), Macdonald (1959) and Shotwell (1963). It was recombined as Hippidion spectans by Trouessart (1892), Trouessart (1898) and Hay (1902); it was recombined as Protohippus spectans by Matthew (1909); it was considered a nomen dubium by Macdonald (1992). It was again recombined as Dinohippus spectans by Creely and et al. (1982), Kelly and Lander (1988), Hulbert (1989), Kelly (1995) and Kelly (1998).^[14][15]

Sister taxa

Astrohippus, Calippus, Equus (synonymized with Allozebra, Asinus, Onager, Plesippus, Neohippus, Equus semiplicatus, Equus tau), Hippidion, Onohippidium, Pliohippus, Protohippus (syn. Eoequus)

References