Class Mammalia
Order Perissodactyla
Family Equidae
Winans (1989) recognized two species (or species groups) of stout-legged horses in the late Rancholabrean of North America: large horses which she assigned to the Equus laurentius group and a small horse assigned to the E. alaskae group. She did note (p. 295) that "It is possible that some of the groups which I have defined encompass more than one species, . . ." Harris and Porter (1980) recognized three species: E. scotti (later re-identified as E. occidentalis by Harris [2013]), E. niobrarensis, and E. conversidens. Based on tooth enamel patterns, Barrón-Ortiz and Theodor (2011:148) found three morphological groups of stout-legged Equus in the late Pleistocene: ". . . a medium stout-legged equid (specimens previously identified as E. conversidens, E. fraternus, and E. lambei), a large stout-legged horse (specimens previously identified as E. complicatus, E. niobrarensis, and E. mexicanus) and E. occidentalis." In contrast, Weinstock et al. (2005) suggested that based on molecular data, a single species of caballine (=stout-legged) horses and a single species of stilt-legged horses may have have made up the entire North American late Pleistocene equine fauna. It should be noted, however, that their sample is highly biased toward northern North America with only one specimen (from Gypsum Cave, Nevada) from south of Wyoming.
The conclusions of Weinstock et al. (2005) do not hold up with the morphological data from the Southwest. Weinstock et al. imply that the morphological differences seen within North American stout-legged horses are adaptations of a single species to different environments. However, occurrences of two to three "morphological species" in what basically is geographic and chronologic sympatry (as at Dry Cave) renders this unlikely since interbreeding would quickly break down the morphological differences. On the other hand, it is easy to visualize different species morphologically adapted to different environments occasionally overlapping in space and time.
In attempting to characterize the equine fauna of Dry Cave, measurements of horses from McKittrick and Rancho La Brea were taken as representing E. occidentalis, and those from San Josecito Cave as representing E. conversidens. No suite of measurements suitable for multivariate analyses for E. niobrarensis were available to me except those identified as such from Dry Cave (I consider the summary measurements of Winans' [1985] Rancholabrean "big horses" to include both E. occidentalis and E. niobrarensis).
Separation of the Dry Cave horses (plus a few from other sites in New Mexico) into multivariate categories equivalent to the samples of E. occidentalis and E. niobrarensis left an intermediate category hypothesized as a third species, E. niobrarensis. This is shown especially well in a cluster dendrogram (Gower paired-group) of second phalanges (Fig. 1).
Fig. 1. Dendrogram showing clustering of second phalanges, interpreted as representing E. conversidens (red), E. niobrarensis (blue-green), and E. occidentalis (magenta). Specimens with labels starting with 192/ are from San Josecito Cave; those starting with CIT are from McKittrick; the remainder are from UTEP specimens.
Utilizing a variety of univariate measurements, the specimens used as representing E. occidentalis and E. conversidens agree well with Winans' (1985) summary univariate statistics for Rancho La Brea and San Josecito, respectively, indicating correct assignments. The Southwestern specimens hypothesized as E. niobrarensis, which would be placed in the "big horses" category by Winans (1985), differ in various measurements (e.g., proximal metacarpal width) from Winans Rancho La Brea sample (also in Winans' "big horses" category) by p = <0.001; that sample also differs from Winans' San Josecito sample ("little horses") by p = <0.001. The overall result of both univariate and multivariate analyses is division into three groups best considered as separate species. It thus appears that the late Rancholabrean large horses of Winans include at least two species.
Literature.
Harris and Porter 1980; Winans 1985, 1989
Synonyms. Equus alaskae, Equus semiplicatus.
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. 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. At 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 while freely acknowledging that
Winans may be technically correct.
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. 2. 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.
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.
Sites.
Quaternary: Nash Draw (Harris 1993c: ?).
Pleistocene: Mockingbird Gap (Morgan and Lucas 2005); Sapillo Creek (Wolberg 1980); Tucumcari (Morgan and Lucas 2005).
Rancholabrean: Badlands Ranch (Morgan and Lucas 2005); Roswell (Morgan and Lucas 2005); Starvation Draw (Morgan and Lucas 2005).
Late Rancholabrean: Mountain Breeze (Morgan and Lucas 2005).
Mid Wisconsin: Papago Springs Cave (Czaplewski and Mead et al. 1999); Pendejo Cave (Harris 2003); U-Bar Cave (Harris 1987).
Mid/Late Wisconsin: Dark Canyon Cave (Tebedge 1988); Hampton Court (Harris and Porter 1980); NW Talus Slope (Harris and Porter 1980); Pit N&W Animal Fair (Harris 1993c).
Mid/Late Wisconsin/Holocene: Sierra Diablo Cave (UTEP).
Late Wisconsin: Algerita Blossom Cave (Harris 1993c); Animal Fair (Harris 1993c; Harris and Porter 1980); Balcony Room (Harris 1993c); Big Manhole Cave (Harris 1993c); Bison Chamber (Harris 1989);Camel Room (Harris 1993c: cf.); Charlies Parlor (Harris and Porter 1980); Blackwater Draw Fauna (Lundelius 1972); Fain Ranch (Pasenko and Agenbroad 2012: cf.); Harris' Pocket (Harris and Porter 1980); Howell's Ridge Cave (Harris 1993c:cf.); Human Corridor (Harris and Porter 1980); Jal Horse Quarry (Schultz 1943);Mystery Light Cave (this volume: cf.); Omega Cave (Harris 1993c); Pendejo Cave (Harris 2003); Salt Creek (UTEP: cf.); Stalag 17 (Harris and Porter 1980); Shelter Cave (this volume); TT II (Harris and Porter 1980); U-Bar Cave 13-14 ka (Harris 1989); U-Bar Cave 14-15 ka (Harris 1989: cf.).
Late Wisconsin/Holocene: Burnet Cave (Harris 1993c); Isleta Cave No. 2 (Harris 1993c: cf.); Pendejo Cave (Harris 2003); Williams Cave (Ayer 1936).
Literature.
Ayer 1936; Czaplewski and Mead et al. 1999; Fiedel 2009; Harris 1987, 1989, 1993c, 2003; Harris and Porter 1980; Lundelius 1972; Morgan and Lucas 2005; Pasenko and Agenbroad 2012; Schultz 1943; Tebedge 1988; Winans 1985, 1989; Wolberg 1980.
Synonyms. Equus caballus caballus, E. caballus laurentius, E. excelsus, E. laurentius, E. midlandensis, E. scotti of the Southwest.
Horse taxonomy has been plagued by an overload of described forms. The taxon recognized by Harris and Porter (1980) as E. niobrarensis appears to have been recognized under a number of synonyms (for reasoning behind the synonymy, see Harris and Porter 1980; Winans 1985). Equus laurentius, especially, has been used relatively recently in the literature. However, Scott et al. (2003), in a poster presentation, and later in a full, evidenced publication (Scott et al. 2010), showed that E. laurentius is based on modern domestic horse material only a few hundred years old. Various other authors, including Winans (1985), also have suggested this (interestingly, Winans in her 1989 work nevertheless applied the name to one of her species groups). Winans (1985) considered E. niobrarensis to be a synonym of E. scotti and, in her 1989 paper, assigned the Dry Cave horses to E. mexicanus, to which she also assigned the Rancho La Brea horses generally labeled as E. occidentalis. See the latter account for the problems with this assignment. Also, Scott et al. (2010) note a problem with the name, E. mexicanus.
Fig. 1. Comparison of first phalanges of E. niobrarensis (top) and Equus conversidens. Left images are of presumed anterior first phalanges and right images of posterior first phalanges.
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. niobrarensis from E. conversidens.
Sites.
Pleistocene: Agua Negra (Morgan and Lucas 2005); Gobernador (Morgan and Lucas 2005); Jemez Springs (Morgan and Lucas 2005); Nash Draw (Harris 1993c: cf.); Perico Creek (Morgan and Lucas 2005); Plaza Larga Creek (Morgan and Lucas 2003); Steins (Morgan and Lucas 2005); Tome (Morgan and Lucas 2005); West Fork Kutz Canyon (Morgan and Lucas 2005).
Late Irvingtonian or Early Rancholabrean (?): Taiban Creek (Morgan and Lucas 2005).
Early Rancholabrean: Albuquerque Gravel Pits (Morgan and Lucas 2005).
Rancholabrean: Alkali Spring (Morgan and Lucas 2005); Casados Ranch (Morgan and Lucas 2005); Jal (Morgan and Lucas 2005); Tramperos Creek (Morgan and Lucas 2005); Twenty Five Mile Stream (Morgan and Lucas 2005).
Mid Wisconsin: Pendejo Cave (Harris 2003); U-Bar Cave (Harris 1987: cf.).
Mid/Late Wisconsin: Dark Canyon Cave (Harris and Porter 1980); Pit N&W Animal Fair (Harris 1993c).
Late Wisconsin: Anderson Basin et al. (Morgan and Lucas 2005); Animal Fair (Harris and Porter 1980); Balcony Room (Harris 1993c); Big Manhole Cave (Harris 1993c); Bison Chamber (Harris and Porter 1980); Blackwater Draw Fauna (Slaughter 1975); Camel Room (Harris and Porter 1980); Charlies Parlor (Harris and Porter 1980); Cueva Quebrada (Lundelius 1984: E. cf. scotti); Harris' Pocket (Harris 1989); Human Corridor (Harris and Porter 1980: ?); Lake Estancia (Morgan and Lucas 2005); Placitas (Hibben 1941); Salt Creek (UTEP: cf.); Sandia Cave, Sandia Level (Hibben 1941); Sandia Gravel Pit (Morgan and Lucas 2005); Stalag 17 (Harris and Porter 1980); TT II (Harris and Porter 1980); U-Bar Cave 14-15 (Harris 1989: cf.).
Late Wisconsin/Holocene: Isleta Cave No. 1 (Harris 1993c: cf.); Isleta Cave No. 2 (Harris 1993c: cf.); Burnet Cave (Schultz and Howard 1935); Beyond Bison Chamber (Harris 1993c: cf.).
Literature.
Harris 1987, 1989, 1993c, 2003; Harris and Porter 1980; Hibben 1941; Lundelius 1984; Morgan and Lucas 2003, 2005; Schultz and Howard 1935; Scott et al. 2003; Scott et al. 2010; Slaughter 1975; Winans 1985, 1989.
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.
Sites.
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).
Literature.
Bennett 1980; Colbert 1950); Harris 1987, 1989, 1993c; Harris and Porter 1980; Hibben 1941; Willoughby 1974; Winans 1985.
Last Update: 16 Jun 2013