Onychomys sp.—Grasshopper Mice // Onychomys arenicola—Mearn's Grasshopper Mouse // Onychomys leucogaster—Northern Grasshopper Mouse // Onychomys pedroensis—San Pedro Grasshopper Mouse // Onychomys torridus-type—Onychomys torridus-type.
Grasshopper mice are represented today by two species in our region, O. leucogaster (Northern Grasshopper Mouse) and O. arenicola (Mearn's Grasshopper Mouse). These more or less represent northern and southern distributions, but with a broad area of overlap in our region.
Onychomys differs from Peromyscus and Reithrodontomys in a number of ways, but discrimination of fossils is largely dependent on mandible and dental characteristics. The cheekteeth of Onychomys are simpler than those of either of the two other genera mentioned, having cusps separated by relatively broad reentrants lacking styles or cuspids (Fig. 1). Dentaries, unlike those of Peromyscus, have large coronoid processes (see figure in the Peromyscus account).
Fig. 1. Lateral view of left dentary. The broad reentrants of m1 are apparent.
Grasshopper mice are more predatory than most mice and, although they will take seeds as part of their diet, they depend heavily on arthropods and are infamous among mammalogists for "running" a trap line and feeding on the captives. Riddle (1999b:589) notes that "a convincing case can be made for viewing these animals as being well-adapted to a predatory existence analogous in many ways to large mammalian carnivores."
Literature. Riddle 1999b.
Several records document the presence of the genus but the species is indeterminate.
Late Blancan: La Union (Morgan and Lucas 2003).
Mid Wisconsin: Papago Springs Cave (Czaplewski and Mead et al. 1999); Tank Trap Wash (Van Devender et al. 1987).
Late Wisconsin: Bennett Ranch #1 (Van Devender and Bradley 1990); Brass Cap Point (Mead et al. 1983); Murray Springs (Mead et al. 2005); Navar Ranch (Van Devender et al. 1987); Wolcott Peak (Mead et al. 1983).
Literature.Czaplewski and Mead et al. 1999; Mead et al. 1983; Mead et al. 2005; Morgan and Lucas 2003; Van Devender and Bradley 1990; Van Devender et al. 1987.
Synonyms. Onychomys torridus.
Until 1979, southern populations of Onychomys were assigned to a single species, O. torridus. At that time, chromosome morphology showed that there were consistent differences between populations to the west and those to the east. Later studies of protein and mitochondrial DNA have strengthened the evidence that two separate species are involved (Riddle 1999a). As currently known, O. arenicola is distributed throughout the lower portions of Trans-Pecos Texas and southern and central New Mexico except for a small area in the southwestern part of the state immediately adjacent to Arizona.
Characteristics of O. arenicola are similar to those of O. leucogaster except that the former is slightly smaller.
Mid/Late Wisconsin/Holocene: Sierra Diablo Cave (UTEP).
Late Wisconsin: Lower Sloth Cave (Logan 1989).
Late Wisconsin/Holocene: Fowlkes Cave (Dalquest and Stangl 1984b); Muskox Cave (Logan 1981); Pendejo Cave (Harris 2003).
Literature. Dalquest and Stangl 1984b; Harris 2003; Logan 1981, 1983; Riddle 1999a.
Onychomys leucogaster is by far the more common grasshopper mouse in the fossil faunas of the region. Today, it is distributed widely in arid and semiarid habitats ranging from sandy areas within creosotebush desert to sagebrush and steppe habitat. Although usually a creature of low to mid elevations in the Southwest, it has been taken in meadows in montane spruce-fir forest (Jones et al. 1960).
Fig. 1. Painting of Onychomys leucogaster by Louis Agassiz Fuertes.
Rancholabrean: Papago Springs Cave (Skinner 1942).
Wisconsin: Big Manhole Cave (Harris 1993c).
Early/Early-Mid Wisconsin: Lost Valley (Harris 1993c).
Mid Wisconsin: Pendejo Cave (Harris 2003); Screaming Neotoma Cave (Glennon 1994).
Mid/Late Wisconsin/Holocene: Sierra Diablo Cave (UTEP)
Mid/Late Wisconsin: Dark Canyon Cave (Harris 1993c); Pit N&W Animal Fair (Harris 1993c).
Late Wisconsin: Animal Fair 18-20 ka (Harris 1989); Brass Cap Point (Mead et al. 1983); Cueva Quebrada (Lundelius 1984); Harris' Pocket (Harris 1970a); Lower Sloth Cave (Logan 1983); Muskox Cave (Logan 1981); Screaming Neotoma Cave (Glennon 1994); Stalag 17 (Harris 1993c); TT II (Harris 1993c); U-Bar Cave 14-15 ka (Harris 1989).
Late Wisconsin/Holocene: Balcony Room (Harris 1993c); Fowlkes Cave (Dalquest and Stangl 1984b); Isleta Cave No. 1 (Harris 1993c); Isleta Cave No. 2 (Harris 1993c); Pendejo Cave (UTEP); Sheep Camp Shelter (Harris 1993c).
Literature. Dalquest and Stangl 1984b; Glennon 1994; Harris 1970a, 1989, 1993c, 2003; Logan 1981, 1983; Lundelius 1984; Jones et al. 1960; Mead et al. 1983; Skinner 1942.
The species is more robust and larger than the extant O. leucogaster and with the lower third molar less reduced (Gazin 1942).
Late Blancan: 111 Ranch (Morgan and White 2005); Curtis Ranch (Gazin 1942).
Literature. Gazin 1942; Morgan and White 2005.
Onychomys torridus-type is used here to indicate one of the smaller grasshopper mice (O. arenicola or O. torridus. The southwestern New Mexican records are close to the current division line between those two species, as is the Murray Springs record (though more surely within the O. torridus present range). The records (as O. torridus) from Isleta No. 1 and Isleta No. 2 are rejected pending further study.
Mid/Late Wisconsin: U-Bar Cave (Harris 1993c).
Late Wisconsin: Murray Springs (Mead et al. 2005).
Late Wisconsin/Holocene: Howell's Ridge Cave (Harris 1993c).
Isleta Cave No. 1 (Harris 1993c); Isleta Cave No. 2 (Harris 1993c).
Literature. Harris 1993c; Mead et al. 2005.
Last Update: 9 Mar 2013