Ectocion

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] It reached 6 to 12 kg and was similar in size and morphology to Copecion. Both these herbivorous ungulates likely occupied similar ecological niches.^[4]

Ectocion Temporal range: Paleocene - Eocene
Ectocion osbornianus
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Family:	†Phenacodontidae
Genus:	†Ectocion Cope, 1882
Species
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

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.^[5]