2010 Overboard in the Mojave - Biological Science - California State ...

on inland lakes, such as the Salton Sea, Imperial County.
The remaining species frequent coastal marine waters or
inland areas from the San Joaquin Valley, central California
northward (Pyle, 1961; Cogswell and Christman,
1977; Garrett and Dunn, 1981) (Table 2).
Extant species of migratory birds represented in the
assemblage are presently absent from southern California
during the summer (Pyle, 1961). They migrate northward
in the spring following inland portions of the north–
south Pacific Coast fly-way. During Pleistocene pluvial
periods, this fly-way would have included the lakes of the
Colorado and Mojave Deserts, those east of the Sierra
Nevada Mountains, and the western part of Lake Lahontan
(Snyder et al., 1964). Many of these species are also
known from the late Pleistocene deposits of China Lake,
Inyo County, California, and Fossil Lake, Lake County,
southeastern Oregon ( Jefferson, 1985b).
Two-thirds of the extant species (Gavia arctica,
Podiceps nigricollis, Aechmophorus occidentalis, Pelecanus
erythrorhynchos, Phalacrocorax auritus, Mergus merganser,
Haliaeetus leucophalus, Aquila chrysaetos, and Larus spp.),
represented by 80% NISP of the fossil avian specimens
(Table 3), presently prefer or feed exclusively on small
fish (Cogswell and Christman, 1977; Garrett and Dunn,
1981). Gila bicolor mojavensis represents an abundant
food source for these predators. Modern representatives
of the remaining taxa (Cygnus columbianus, Branta
canadensis, Anas crecca, Anas platyrhynchos, Aythya sp.,
Oxyura jamaicensis, Fulica americana, Grus sp., Actitis sp.),
feed on a variety of water plants and freshwater invertebrates
(Cogswell and Christman, 1977; Garrett and
Dunn, 1981). The owl, Bubo virginianus, is the only bird in
the assemblage that feeds primarily on small mammals.
Mammalian herbivores
Among the larger herbivores, three taxa of ground sloth,
Megalonyx, Paramylodon, and Nothrotheriops, are present.
All are poorly represented in the assemblage (Table
4). Megalonyx is known from the West Coast and eastern
two-thirds of the United States, and ranged from South
America into Canada and Alaska. Stock (1925) suggested
that this animal was adapted to forest or woodland habitats.
The habitat and dietary preferences of Paramylodon,
which also ranged through North and South America, are
not well known. Given its association with other presumed
grassland animals, Stock (1925, 1930) maintained
that Paramylodon was a grazer. Based on analysis of the
feeding mechanism in Paramylodon, Naples (1989) argued
that it was a grazer-browser. Considering the varied
environments within an extensive geographic range, both
Megalonyx and Paramylodon were probably mixed feeders.
Nothrotheriops shastensis ranged throughout the
george t. jefferson
southwestern United States and northern Mexico. It is
well represented in cave assemblages from northeastern
California through southern Nevada, and Arizona
where it browsed on desert shrubs and plants typical of a
juniper-sage brush savannah habitat (Martin et al., 1961;
Hansen, 1978). This selective folivore/browser (Naples,
1987) appears to have inhabited a broad spectrum of
floral assemblages, but was limited latitudinally and altitudinally
by minimum winter temperatures (McDonald et
al., 1996).
Lepus sp. is the only small mammalian herbivore well
represented in the assemblage. Jack rabbits typically inhabit
grassy and brush covered areas. The order Rodentia
is represented by a single cricetid humerus.
The relatively abundant but fragmentary remains of
mammoth can not be identified to species. However, they
probably represent the well-known middle and late Pleistocene
form, Mammuthus columbi (= M. imperator). M.
columbi ranged throughout the United States and likely
browsed and/or grazed (Davis et al., 1984) in small herds
similar to extant elephants. Evans (1961) suggested that
juvenile mammoths were the favored prey of the scimitartooth
cat, Homotherium serum. The American mastodon,
Mammut americanum, is absent in the assemblage, and has
not been identified from any Rancholabrean LMA sites
within the Mojave Desert or Colorado Desert regions
( Jefferson, 1991c).
Fossil horses are well represented in the assemblage
(Table 4), and at least two forms, Equus conversidens and
Equus sp. (large) have been identified. The occurrence
Table 4. Relative abundance of mammalian taxa,
Manix Formation
Taxon NISP % NISP
Megalonyx sp. _ 1 0.1
Nothrotheriops sp. cf. N. shastensis _ 2 0.3
Paramylodon sp. _ 1 0.1
Mammuthus sp. _ 37 5.2
Lepus sp. 11 1.6
Cricetidae 1 0.1
Canis sp. cf. C. dirus _ 5 0.7
Canis latrans 5 0.7
Arctodus sp. _ 1 0.1
cf. Ursus sp. 1 0.1
Felis (Puma) sp. 3 0.4
Homotherium sp. cf. H. crenatidens _ 1 0.1
Homotherium sp. cf. H. serum _ 2 0.3
Equus conversidens _ 52* 7.4
Equus sp. (large-size) _ 67* 9.5
Camelops sp. cf. C. hesternus _ 371 54.7
Camelops sp. aff. C. minidokae _ 5 0.7
Hemiauchenia macrocephala _ 117 16.6
Antilocapara sp. 2 0.3
Ovis canadensis 17 2.5
Bison sp. cf. B. antiquus _ 1 0.1
Note: Total number of identified specimens is 703, and total % NISP is
101.5. Data are in part from Jefferson (1985a, 1987).
NISP = number of identified specimens
% NISP = number of specimens identified for each taxon divided by the
total number of identified specimens
* = may represent more than one species _ = extinct taxon
48 2010 Desert Symposium