Equus calobatus—Stilt-legged Onager // Equus cumminsii—Cummins's Ass // Equus francisci—Stilt-legged Onager // Equus fraternus—Fraternal Horse
The position of this taxon in relation to E. francisci is unclear. Kurtén and Anderson (1980) cite E. calobatus as the largest of the stilt-legged horses (subgenus Hemionus), whereas E. francisci (E. tau of Kurtén and Anderson) is said to be the smallest of the North American Pleistocene horses (Dalquest 1979). Winans (1985) considered E. calobatus to be a junior synonym of E. francisci. Vanderhill (1986), in considering Blancan to Irvingtonian specimens from fossil beds revealed by the incision of the Rio Grande Valley, referred material to this taxon, retaining E. calobatus as valid.
Late Blancan: 111 Ranch (Morgan and White 2005: ?); La Union (Morgan and Lucas 2003: ?); Santo Domingo (Morgan and Lucas 2003: ?).
Early Irvingtonian: Adobe Ranch (Morgan and Lucas 2003: cf.).
Irvingtonian: El Paso (UTEP).
Dalquest 1979; Kurtén and Anderson 1980; Morgan and Lucas 2003; Morgan and White 2005; Vanderhill 1986; Winans 1985.
Kurtén and Anderson (1980) viewed this species as belonging to the subgenus Asinus. Also see the discussion in Scott (2005). The species was described on the basis of upper teeth (Gidley 1907), with lower dentition later referred. A lower jaw containing all cheek teeth (Fig. 1) is available from Chihuahua with the only locality data given as "First terrace above Rio Grande floodplain on south side of river." Without more data, it is assumed here to be Blancan Pleistocene, though it could be from apparently pre-Pleistocene Blancan sites such as occur along the Rio Grande Valley immediately downstream to the southeast (Strain 1966; Akersten 1972).
Fig. 1. Right lower toothrow of Equus cumminsii (UTEP 156-1) from the Blancan of Chihuahua, Mexico. The image has been manipulated to better show occlusal details. Length of toothrow at occlusal surface, 152.3 mm.
Late Blancan: 111 Ranch (Morgan and White 2005: ?); First Terrace (UTEP).
Akersten 1972; Kurtén and Anderson 1980; Morgan and White 2005; Scott 2005; Strain 1966.
Synonyms. Equus tau.
Dalquest (1979) considered Equus francisci to be a synonym of Equus tau, and E. tau to be the only small, stilt-legged horse of the Pleistocene. He characterized it as the smallest of the North American Pleistocene horses.
Winan (1985, 1989) considered this a valid species (or species group) of stilt-legged horse. In these, the length to proximal width of the metacarpal is generally greater than 5.0 and that of the metatarsal, greater than 6.0 (Winans 1989).
Occurrence in the Balcony Room site of Dry Cave is based solely on a single, partial upper tooth (Figs. 1 and 2) that is appreciably smaller than that of E. conversidens; teeth from Villa Ahumada likewise are identified to this taxon on the basis of size.
The La Brisca horse remains included a large horse and E. cf. tau, with the latter tentatively identified on the basis of small size (Van Devender et al. 1985).
Fig. 1. Occlusal views of an upper cheek tooth of E. conversidens (left) and that of E. francisci (right). Scale is in mm.
Fig. 2. Longitudinal lateral and internal views of the specimen identified as E. francisci. Scale in mm.
Rancholabrean: Papago Springs Cave (Skinner 1942); Villa Ahumada (UTEP: ?).
Sangamon: La Brisca (Van Devender et al. 1985).
Mid/Late Wisconsin/Holocene: Sierra Diablo Cave (UTEP).
Late Wisconsin: Balcony Room (Harris 1993c); Bonfire Shelter (Bement 1986); Burnet Cave (Schultz and Howard 1935: cf.); Cueva Quebrada (Lundelius 1984); White Mesa (Morgan and Rinehart 2007: cf.).
Bement 1986; Dalquest 1979; Harris 1993c; Lundelius 1984; Morgan and Rinehart 2007; Schultz and Howard 1935; Skinner 1942; Van Devender et al. 1985; Winan 1985, 1989.
This is considered a nomen dubium by Winans (1985). Cosgrove (1947) gives no information that would allow placement to any currently recognized species of our region.
Pleistocene. Ceremonial Cave (Cosgrove 1947).
Cosgrove 1947; Winans 1985.
Last Update: 8 Nov 2013