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Class Mammalia
Order Perissodactyla
Family Equidae


Equus conversidens—Mexican Horse // Equus occidentalis—Western Horse // Equus pacificus—Pacific Horse // Equus scotti—Scott's Horse

†Equus conversidens Owen 1869—Mexican HorseRegional Pleistocene distribution of Equus conversidens

Synonyms. Equus alaskae, Equus semiplicatus.

Scott (1996) noted that there are three incompatible morphological concepts of Equus conversidens in the literature: a small, stout-legged horse with a lack of infundibulae in the lower incisors and with the molar ectoflexids not entering into the metaconid-metastylid isthmus; a horse with similar morphology but having infundibulae in the lower incisors; and a horse similar to the latter but having stilt-legged metapodials. The first definition is that followed here and by Harris and Porter (1980) among a number of other researchers.

Equus deciduous and permanent incisors lacking infundibula The nomenclatural position of the medium-small horse with only moderately slender metapodials (ratio of the length to the proximal width of the metacarpal generally less than 5.0 and that of the metatarsal less than 6.0) has been all over the place, as noted above. Winans (1985) treated E. conversidens as a nomen nudum since it was named solely on the basis of dental characters, which she found non-diagnostic. However, the name has been widely used. In recent times, the name E. alaskae has been used in the literature based on the treatment of species or species groups of Winans (1985, 1989). I have chosen to retain the name E. conversidens for this medium-small, extinct horse.

Several specimens of lower incisors assigned by Harris and Porter (1980) are available and lack an infundibulum. The illustrated specimen (Fig. 1) was referred by Harris and Porter (1980) to E. occidentalis, but since has been compared with a specimen of E. conversidens of similar age and appears to represent the latter species. Width at the di3s is 67.8 mm. The specimen is the same as drawn as Fig. 6 J in Harris and Porter (1980).

Fig. 1. Anterior lower jaw of Equus showing the lack of an infundibulum in i1 and i2 and possibly in the deciduous incisors, although di3 is slightly scooped. This has been listed (Harris and Porter 1980) as E. occidentalis, but in comparison with a specimen of E. conversidens of similar age appears to pertain to this species. UTEP 26-1064.

Winans (1989) considered the small horses of Dry Cave, which includes the taxon here, as representative of the Equus alaskae group, and Harris (1993c) listed it under that name.

Tebedge (1988) seemed to indicate that the Dark Canyon Cave specimens fall into this taxon, but being unsure of the nomenclature, merely listed it as Equus sp. Since UTEP horse material from Dark Canyon Cave is identified as E. conversidens, Tebedge's material is recorded as the same.

The third phalanx of this species differ notably from that of E. scotti (Fig. 2), presumably not only as a result of size differences, but of adaptations to different environments. The third phalanx is very similar to that of Equus asinus.

Fig. 2. Third phalanges of Equus scotti (left) and E. conversidens.

Three views of the third phalanges of <i>E. scotti</i> and <i>E. conversidens</i>

In their tables of measurements and figures, Harris and Porter (1980) listed various sites within Dry Cave only by site number; they are cited here by the site name.

The youngest dates cited by Fiedel (2009) for the species are 11,330 ± 70 and 10,870 ± 45 BP.


Quaternary: Nash Draw (Harris 1993c: ?).

Pleistocene: Mockingbird Gap (Morgan and Lucas 2005); Sapillo Creek (Wolberg 1980); Tucumcari (Morgan and Lucas 2005).

Irvingtonian: El Golfo (Croxen et al. 2007: cf.).

Irvingtonian/Rancholabrean: Manix Lake (Jefferson 1991b: cf.).

Early Rancholabrean: Shoshone Zoo (Jefferson 2014).

Rancholabrean: Badlands Ranch (Morgan and Lucas 2005); Bitter Springs Playa (Jefferson 1991b: cf.); Canovas Creek (Morgan 2015); Goler Gulch (Jefferson 2014); Pinto Basin (Jefferson 1991c: cf.); Piute Valley (Jefferson 1991b: cf., withdrawn [Jefferson 2014]); Rancho de Enmedio (White et al. 2010); Roswell (Morgan and Lucas 2005); Starvation Draw (Morgan and Lucas 2005); Tesopaco (Carranza-Castañeda and Roldán-Quintana 2007); United Energy Solar Ponds (Jefferson 1991b: cf.); Valley Wells (Jefferson 1991b: cf., withdrawn).

Late Rancholabrean: Mountain Breeze (Morgan and Lucas 2005).

Early Wisconsin: Stevens Lake (Jefferson 1991b).

Mid Wisconsin: Papago Springs Cave (Czaplewski and Mead et al. 1999); Pendejo Cave (Harris 2003); Te´rapa (Carranza-Castañeda and Roldán-Quintana 2007); U-Bar Cave (Harris 1987).

Mid/Late Wisconsin: Big Manhole Cave (Harris 1993c; UTEP); Dark Canyon Cave (Tebedge 1988); Diamond Valley (Springer et al. 2009); Hampton Court (Harris and Porter 1980); NW Talus Slope (Harris and Porter 1980); Pit N&W Animal Fair (Harris 1993c); Rancho La Brea (Stock and Harris 1992).

Mid/Late Wisconsin/Holocene: Shelter Cave (Harris data); Sierra Diablo Cave (UTEP).

Late Wisconsin: Algerita Blossom Cave (Harris 1993c); Animal Fair (Harris 1993c; Harris and Porter 1980); Antelope Cave (Reynolds, Reynolds, Bell, and Pitzer 1991); Balcony Room (Harris 1993c); Bison Chamber (Harris 1989); Blackwater Draw Fauna (Lundelius 1972); Burnet Cave (Harris 1993c; Harris data); Camel Room (Harris 1993c: cf.); Charlies Parlor (Harris and Porter 1980); China Lake (Jefferson 1991b: cf.); Conkling Cavern (Harris data); Fain Ranch (Pasenko and Agenbroad 2012: cf.); Gypsum Cave (Jefferson et al. 2015); Harris' Pocket (Harris and Porter 1980); Howell's Ridge Cave (Harris 1993c:cf.); Human Corridor (Harris and Porter 1980); Isleta Cave No. 2 (Harris 1993c: cf.); Jal Horse Quarry (Schultz 1943); Kokoweef Cave (Reynolds, Reynolds, et al. 1991); Mystery Light Cave (this volume: cf.); Omega Cave (Harris 1993c); Pendejo Cave (Harris 2003); Salt Creek (UTEP: cf.); Stalag 17 (Harris and Porter 1980); TT II (Harris and Porter 1980); U-Bar Cave 13-14 ka (Harris 1989); U-Bar Cave 14-15 ka (Harris 1989: cf.); Williams Cave (Ayer 1936).

Literature. Ayer 1936; Carranza-Castañeda and Roldán-Quintana 2007; Croxen et al. 2007; Czaplewski and Mead et al. 1999; Fiedel 2009; Harris 1987, 1989, 1993c, 2003; Harris and Porter 1980, Jefferson 1991b, 1991c, 2014; Jefferson et al. 2015; Lundelius 1972; Morgan 2015; Morgan and Lucas 2005; Pasenko and Agenbroad 2012; Reynolds, Reynolds, et al. 1991; Reynolds, Reynolds, Bell, and Pitzer 1991; Schultz 1943; Scott 1996; Springer et al. 2009); Stock and Harris 1992); Tebedge 1988; White et al. 2010; Winans 1985, 1989; Wolberg 1980.


Equus occidentalis Leidy 1865—Western HorseRegional Pleistocene distribution of Equus occidentalis

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) treated E. occidentalis as a nomen dubium and assigned the Rancho La Brea horse to E. mexicanus. In her 1989 paper, Winans included E. mexicanus in her E. laurentius group and assigned the larger horses from Dry Cave to that group. It should be understood that my use of E. occidentalis is solely to indicate relationship to the Rancho La Brea horse, and is not meant as a nomenclatural statement.

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 associates nicely with the Rancho La Brea specimens in cluster and principal components analyses (see Fig. 2 of the Equus account). 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 infundibulae (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 the name of E. scotti.


Early Irvingtonian: Adobe Ranch (UTEP).

?Late Irvingtonian/Rancholabrean: Emery Borrow Pit (Jefferson 1991b).

Rancholabrean: Arbogast Ranch (Jefferson 1991b: cf.); Bakersfield Canal Cutting (Jefferson 1991b); Camarillo Hills (Jefferson 1991b); Canovas Creek (Morgan 2015); Cool Water Coal Gasification Site (Jefferson 1991b); Coronado Beach, San Diego (Jefferson 1991b); Irish Canyon (Jefferson 1991b: cf.); Lake View Hot Springs (Jefferson 2014: cf.); Metro Rail Hollywood Tunnel (Jefferson 2014); Nash Draw (UTEP: ?); Park La Brea A (Jefferson 2014);Park La Brea B (Jefferson 2014); San Buenaventura (Jefferson 1991b); Santa Maria Oil Spring (Jefferson 1991b); Santa Paula (Jefferson 1991b).

Wisconsin: Carpinteria (Wilson 1933: cf.).

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

Mid Wisconsin: McKittrick (Schultz 1937); Pendejo Cave (UTEP: ?); U-Bar Cave (Harris 1987: cf.).

Mid/Late Wisconsin: Diamond Valley (Springer et al. 2009); Rancho La Brea (Stock and Harris 1992: cf.); U-Bar Cave (UTEP).

Late Wisconsin: Balcony Room (Harris 1993c: ?); Calico Lakes (Jefferson 1991b: cf.); Charlies Parlor (UTEP); China Lake (Jefferson 1991b: cf.); Dove Springs Megafaunal Loc. (Jefferson 2014: cf.); Gypsum Cave (Jefferson et al. 2015: cf.); Human Corridor (Harris 1993c); Isleta Cave No. 2 (UTEP); Luz Solar Trough (Jefferson 1991b); Salt Creek (UTEP: ?); Sandia Cave, Folsom Level (Hibben 1941: cf.); Solar One (Jefferson 1991b: cf.); Ventana Cave (Colbert 1950).

Literature. Bennett 1980; Colbert 1950); Harris 1987, 1989, 1993c; Harris and Porter 1980; Hibben 1941; Jefferson 1991b, 2014; Jefferson et al. 2015; Morgan 2015; Schultz 1937; Springer et al. 2009); Stock and Harris 1992); Willoughby 1974; Wilson 1933); Winans 1985.


Equus pacificus Leidy 1868—Pacific HorsePleistocene regional distribution of Equus pacificus


Late Blancan/Irvingtonian: Anza-Borrego (Murray 2008: ?).

Rancholabrean: Las Vegas Wash, Big Wash (Jefferson et al. 2015).

Literature. Jefferson et al. 2015; Murray 2008.


Equus scotti Gidley 1900—Scott's HorseRegional Pleistocene distribution of Equus scotti

Synonyms. Equus bautistensis, Equus caballus caballus, E. caballus laurentius, E. excelsus, E. laurentius, E. midlandensis, E. niobrarensis.

Comparison of the first phalanges of Equus conversidens and Equus scotti

Fig. 1. Comparison of the first phalanges of E. scotti (top) and E. conversidens (bottom). Anterior phalanges are on the left and posterior phalanges on the right.

This is a medium-size horse that commonly occurs together with E. conversidens in Southwestern fossil faunas. Harris and Porter (1980) give a number of measurements separating E. scotti (as E. niobrarensis) from E. conversidens.

Equus scotti p3-m3

Scott (1998:76A) synonymized Equus bautistensis with E. scotti, basing this on:

1) large size; 2) short, stout metapodials; 3)bilobate protocones in P3-4 with a strong anterior heel; 4) ectoflexids in M1-2 which approach but do not fully penetrate the molar isthmus; and 5) closed infundibulae in I1-2 and an open infundibulum in I3.

Fig. 2 (far right). Right p3-m3 of E. scotti (UTEP 22-1528) showing the cheek tooth characteristics of E. scotti.

Equus scotti R p4 Equus scotti anterior lower jaw showing L i1-2 and R i1-3

Fig. 3 (left). Anterior lower jaw of E. scotti showing L i1-2 and R i1-3.
Fig. 4 (near right). Right P4 of
E. scotti showing nature of the protocone (bottom of figure).

Many of the records listed below were published as E. niobrarensis. Pending general acceptance of E. niobrarensis as a synonym of E. scotti (assuming such acceptance occurs), separate lists of site records are given for those published as E. niobrarensis but not examined by me on the one hand and for sites from which I have identified E. scotti, on the other.

Sites: A Site records for horse remains identified in the literature as E. niobrarensis (or synonyms) and not studied by me.

Pleistocene: Agua Negra (Morgan and Lucas 2005); Denton Ranch (Morgan and Lucas 2006); Gobernador (Morgan and Lucas 2005); Jemez Springs (Morgan and Lucas 2005); Perico Creek (Morgan and Lucas 2005); Plaza Larga Creek (Morgan and Lucas 2003); Sandia Gravel Pit (Morgan and Lucas 2003); Tome (Morgan and Lucas 2005); West Fork Kutz Canyon (Morgan and Lucas 2005).

Late Blancan/Early Irvingtonian: Elsinore: Mimomys (Pajak et al. 1996).

Irvingtonian: Bautista Badlands (Frick 1921); Elsinore: Microtus/Mammuthus (Pajak et al. 1996).

Early Irvingtonian: El Casco, San Timoteo Badlands (Albright 2000).

Late Irvingtonian: Elsinore: Pauba Formation (Pajak et al. 1996).

Late Irvingtonian or Early Rancholabrean (?): Taiban Creek (Morgan and Lucas 2005).

Rancholabrean: Alkali Spring (Morgan and Lucas 2005); Casados Ranch (Morgan and Lucas 2005); Jal (Morgan and Lucas 2005); Park La Brea A (Jefferson 2014); Tramperos Creek (Morgan and Lucas 2005); Twenty Five Mile Stream (Morgan and Lucas 2005).

Early Rancholabrean: Albuquerque Gravel Pits (Morgan and Lucas 2005).

Mid Wisconsin: T&eacue;rapa (Carranza-Castañeda and Roldán-Quintana 2007).

Late Wisconsin: Anderson Basin et al. (Morgan and Lucas 2005); Blackwater Draw Fauna (Slaughter 1975); Lake Estancia (Morgan and Lucas 2005); Sandia Cave, Sandia Level (Hibben 1941); Sandia Gravel Pit (Morgan and Lucas 2005);

Sites: B Sites from which I have identified horse remains as E. scotti or which have been identified in the literature as E. scotti. Material that I have reexamined since it was originally published as E. niobrarensis has a citation to the publication and the acronym UTEP.

Pleistocene: Lemitar (Morgan et al. 2009: cf.); Nash Draw (Harris 1993c, UTEP); Steins (Morgan and Lucas 2005, UTEP: ?).

Latest Blancan: Caballo (Morgan et al. 2011); La Union (Morgan and Lucas 2003); Santo Domingo (Morgan and Lucas 2003); Virden (Morgan and Lucas 2003).

Irvingtonian: El Golfo (Croxen et al. 2007: aff.).

Early Irvingtonian: Hells Canyon (Morgan and Lucas 2005); Adobe Ranch (Morgan and Lucas 2003); Tijeras Arroyo (Morgan and Lucas 2005).

Medial Irvingtonian: Gutierrez Gravel Pit (Morgan and Lucas 2005).

Mid Wisconsin: Lost Valley (UTEP); Pendejo Cave (Harris 2003; UTEP); U-Bar Cave (Harris 1987; UTEP).

Mid/Late Wisconsin: Dark Canyon Cave (Harris and Porter 1980; UTEP: cf.); Pit N&W Animal Fair (Harris 1993c; UTEP: ?).

Late Wisconsin: Algerita Blossom Cave (UTEP); Animal Fair (Harris and Porter 1980; UTEP); Balcony Room (Harris 1993c; UTEP); Big Manhole Cave (Harris 1993c; UTEP); Beyond Bison Chamber (Harris 1993c; UTEP: cf.); Bison Chamber (Harris and Porter 1980; UTEP: ?); Burnet Cave (Schultz and Howard 1935, Harris data); Camel Room (Harris and Porter 1980; UTEP); Charlies Parlor (Harris and Porter 1980; UTEP); Circus Route (UTEP); Conkling Cavern (Harris data); Cueva Quebrada (Lundelius 1984: cf.); Harris Pocket (Harris 1989; UTEP); Human Corridor (Harris and Porter 1980; UTEP: cf.); Isleta Cave No. 1 (Harris 1993c; UTEP); Isleta Cave No. 2 (Harris 1993c; UTEP); Placitas (Hibben 1941; UTEP: ?); Salt Creek (UTEP: cf.); Shelter Cave (Harris data: cf.); Sierra Diablo Cave (UTEP: cf.); Stalag 17 (Harris and Porter 1980; UTEP); TT II (Harris and Porter 1980; UTEP); U-Bar Cave 14-15 ka (Harris 1989; UTEP: cf.).

Literature. Croxen et al. 2007; Frick 1921; Harris 1987, 1989, 1993c, 2003; Harris and Porter 1980; Hibben 1941; Jefferson 1991b; Lundelius 1984; Morgan and Lucas 2003, 2005, 2006; Schultz and Howard 1935; Scott 1998; Scott et al. 2003; Scott et al. 2010; Slaughter 1975; Winans 1985, 1989.


Last Update: 29 Sep 2015