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Class Mammalia
Order Perissodactyla
Family Equidae


Equus occidentalis Leidy 1865—Western HorsePleistocene distribution of Equus occidentallis

The position of E. occidentalis in relation to other Southwestern taxa is unclear, with the taxon having been erected on the basis of an isolated tooth that does not appear diagnostic at the species level. The Rancho La Brea horse has long been assigned to this species, but because the name cannot be associated with diagnostic material, Winans (1985) treats E. occidentalis as a nomen dubium and assigns the Rancho La Brea horse to E. mexicanus. In her 1989 paper, Winans includes E. mexicanus in her E. laurentius group and assigns the larger horses from Dry Cave to that group.

Winans' assignment of the larger Dry Cave horses to a taxon equivalent to E. occidentalis creates a problem, however. Relying on measurements by Willoughby (1974) of the Rancho La Brea (RLB) specimens traditionally treated as E. occidentalis (= Winans' E. mexicanus), the Dry Cave (DC) horses average smaller with the exception of the horse (UTEP 31-57) identified by Porter and Harris as E. scotti; the metacarpal of the latter is very close to the means of the RLB metacarpals of E. occidentalis (length: RLB 253 mm, DC 254 mm; width at middle: RLB 38.6 mm, DC 41.4 mm). Another problem is that the Rancho La Brea taxon apparently lacks an infundibulum on any of the lower incisors (Bennett 1980), whereas the Dry Cave horses identified as E. niobrarensis have them.

For the present, the largest elements from the late Wisconsin of Dry Cave, including UTEP 31-57, are referred to E. occidentalis; in view of nomenclatural problems, this assignment is meant only to indicate likely conspecificity with the Rancho La Brea horse. A large anterior lower mandible from the Early or Early Mid Wisconsin with deciduous and permanent incisors lacking infundibuli (UTEP 26-1064) earlier referred to this species is transferred to E. conversidens; see that account). The Dry Cave horses identified by Harris and Porter (1980) as E. niobrarensis are retained under that name.


Early/Early-Mid Wisconsin: Rm Vanishing Floor (Harris and Porter 1980).

Mid Wisconsin: U-Bar Cave (Harris 1987: cf.)

Late Wisconsin: Animal Fair 18-20 ka (Harris 1989: cf.); Balcony Room (Harris 1993c: ?); Charlies Parlor (Harris 1989: ?); Human Corridor (Harris 1993c); Sandia Cave, Folsom Level (Hibben 1941: cf.); Ventana Cave (Colbert 1950).


Bennett 1980; Colbert 1950); Harris 1987, 1989, 1993c; Harris and Porter 1980; Hibben 1941; Willoughby 1974; Winans 1985.


Last Update: 30 May 2013