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Temporal range: Paleocene - Eocene
Ectocion Ralstonensis.jpg
Ectocion osbornianus
Scientific classification e
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Perissodactyla (?)
Family: Phenacodontidae
Genus: Ectocion
Cope, 1882
  • E. cedrus Thewissen, 1990
  • E. collinus Russell, 1929
  • E. ignotum Novacek et al., 1991
  • E. major Patteron & West, 1973
  • E. mediotuber Thewissen, 1990
  • E. nanabeensis Beard & Dawson, 2009[1]
  • E. osbornianus Cope, 1882
  • E. parvus Granger, 1915
  • E. stockeyae Montellano-Ballesteros et al., 2021[2]
  • E. superstes Granger, 1915

Ectocion (sometimes Ectocyon) is an extinct genus of placental mammals of the family Phenacodontidae. The genus was earlier classified as Gidleyina (Simpson 1935) and Prosthecion (Patterson and West 1973)[3]

Paleocene specimens of these hoofed, ground-dwelling herbivores have been found in Canada (Alberta, Saskatchewan) and the United States (Colorado, Montana, North Dakota, and Wyoming). Eocene specimens have been found in Mexico and the United States (Colorado, Mississippi, Wyoming).[3]

One of the dramatic effects of the Paleocene–Eocene Thermal Maximum (PETM) was some animals evolving smaller bodies. Fossilized Ectocion jaw bones show that this genus was smaller during (E. parvus, 55.5 mya) the PETM than its relatives before (E. osbornianus, 55.6 mya) and after (E. osbornianus, 55.3 mya) the brief climatic peak period.[4]


  1. ^ Beard, K. C.; Dawson, M. R. (2009). "Early Wasatchian Mammals of the Red Hot Local Fauna, Uppermost Tuscahoma Formation, Lauderdale County, Mississippi". Annals of Carnegie Museum. 78 (3): 193–243. doi:10.2992/007.078.0301.
  2. ^ Montellano-Ballesteros, M.; Fox, R. C.; Scott, C. S. (2021). "A new, "dwarfed" species of the phenacodontid "condylarth" Ectocion from the late Paleocene of Alberta, Canada, and its implications". Canadian Journal of Earth Sciences: 1155–1169. doi:10.1139/cjes-2019-0234.
  3. ^ a b Ectocion in the Paleobiology Database. Retrieved May 2013.
  4. ^ Gingerich, Phil (2009). "Big Little Big". Smithsonian National Museum of Natural History.