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Dung, diet, and the paleoenvironment of the extinct shrub-ox
(Euceratherium collinum) on the Colorado Plateau, USA
Manny Kropf
a,
⁎, Jim I. Mead
a,c
, R. Scott Anderson
a,b
a
Laboratory of Quaternary Paleontology, Quaternary Sciences Program, Northern Arizona University, Flagstaff, AZ 86011, USA
b
Center for Environmental Sciences and Education, and Quaternary Sciences Program, Northern Arizona University, Flagstaff, AZ 86011, USA
c
Department of Geology, Northern Arizona University, Flagstaff, AZ 86011, USA
Received 17 May 2006
Available online 7 November 2006
Abstract
Fossil remains of Euceratherium collinum (extinct shrub-ox) have been found throughout North America, including the Grand Canyon. Recent
finds from the Escalante River Basin in southern Utah further extend the animal's range into the heart of the Colorado Plateau. E. collinum teeth
and a metapodial condyle (foot bone) have been recovered in association with large distinctively shaped dung pellets, a morphology similar to a
‘Hershey's Kiss’(HK), from a late Pleistocene dung layer in Bechan Cave. HK dung pellets have also been recovered from other alcoves in the
Escalante River Basin including Willow and Fortymile canyons. Detailed analyses of the HK pellets confirmed them to be E. collinum and
indicate a browser-type diet dominated (>95%) by trees and shrubs: Artemisia tridentata (big sagebrush), Acacia sp. (acacia), Quercus (oak), and
Chrysothamnus (rabbit brush). The retrieval of spring and fall pollen suggests E. collinum was a year-round resident in the Escalante River Basin.
© 2006 University of Washington. All rights reserved.
Keywords: Pleistocene; Dung; Bechan Cave; Escalante River Basin; Euceratherium; Paleoenvironment; Microhistology; Pollen
Introduction
The shrub-ox, Euceratherium collinum (Artiodactyla, Rumi-
nantia, Bovidae, Ovibovini), along with several related taxa,
represent a little studied and poorly understood group of extinct
North American ovibovids (Frick, 1937; Scott, 1962; Martin
and Wright, 1967; Nelson and Neas, 1980; Harris, 1985). Eu-
ceratherium is the earliest known ovibovid to enter North
America, appearing in the early Irvingtonian Land Mammal
Age of the Pleistocene, possibly 1.1 Ma (Kurtén and Anderson,
1980). The morphology of the animal and its relationship to
other bovids is inferred from a moderate amount of skeletal
material found in two caves, including the type locality in
northern California (Sinclair and Furlong, 1904; Furlong, 1905;
Sinclair, 1905). Radiocarbon dates taken on dung pellets,
having a distinctive shape resembling a ‘Hershey's Kiss’(HK)
and assumed by Mead and Agenbroad (1992) to belong to
Euceratherium, indicate extinction as late as 11,500
14
CyrBP.
However, the rational for the identification of the dung has not
been presented until now.
One of the most remarkable finds in the American Southwest
has been the preservation of dung remains from Pleistocene
animals such as Mammuthus (mammoth; Mead et al., 1986a),
Nothrotheriops (ground sloth; Martin et al., 1961), and various
pellet-producing artiodactyls, including Oreamnos harringtoni
(Harrington's mountain goat; Mead et al., 1986c) in dry caves
(Davis et al., 1984; Mead et al., 1984; Agenbroad et al., 1989;
Mead and Agenbroad, 1992; Mead et al., 2003). Large
distinctively shaped dung pellets (HK pellets), with an average
cylindrical diameter of 14.5 mm and length of 19.3 mm, tapered
on one end only, with a flat to concave shape on the opposite end
(giving them their distinctive ‘Hershey's Kiss’morphology), are
located in numerous alcoves and caves within the Escalante
River Basin, southern Colorado Plateau (Table 1;Mead and
Agenbroad, 1992). The purpose of this study is to characterize
and identify the HK dung pellets, previously assumed to belong
to Euceratherium collinum, and to describe the diet from
extracted microhistological remains and pollen preserved in the
pellets. This study permits a better understanding of the natural
history of an extinct and enigmatic herbivore.
Quaternary Research 67 (2007) 143 –151
www.elsevier.com/locate/yqres
⁎Corresponding author. 780 South 9th Avenue, Tucson, AZ 85701, USA.
E-mail address: mannyandsusan@netzero.net (M. Kropf).
0033-5894/$ - see front matter © 2006 University of Washington. All rights reserved.
doi:10.1016/j.yqres.2006.10.002
HK pellets are represented in six alcoves on the Colorado
Plateau (Table 1;Fig. 1). Excavations completed in the early
1980s at Bechan Cave first revealed the presence of a stratum,
up to 40 cm thick (>300 m
3
), containing dung (predominantly
Mammuthus) and skeletal remains of Pleistocene mammals
dating between 14,700 and 11,000
14
CyrBP(Mead et al.,
1986a). The HK dung pellets were found in loose association
with E. collinum skeletal remains (a dentary second molar
(M
2
) and a metapodial condyle; Kropf, 2005).
Surveys conducted in Fortymile Canyon and Willow Gulch
in the middle to late 1980s recovered HK pellets, similar in
morphology and size to those found in Bechan Cave (Mead and
Agenbroad, 1992). HK pellet samples were collected from the
loosely compacted flat surface sediments within alcoves and
from sloping erosional deposits. Table 1 presents the alcoves
containing these distinctive dung pellets. HK dung pellets were
dated directly and by stratigraphic association by Mead and
Agenbroad (1992).
Study area
The Escalante River Basin, located in southern Utah at the
center of the Colorado Plateau, contains countless deeply
entrenched canyons formed predominantly in the Navajo
Sandstone. The formation has numerous alcoves and caves
that provide a unique arid habitat for the preservation of late
Pleistocene deposits containing the dry-preserved remains of
plant macrofossils, pollen, dung, and skeletal material (Agenb-
road et al., 1989).
Climate in the Escalante River Basin today is semiarid with
seasonal rains and a mean annual temperature of 10–12°C.
Vegetation communities in the Escalante River Basin include
desert scrub along slick rock areas, riparian vegetation along
permanent stream beds, hanging gardens near seeps, sagebrush
along the dry sandy areas just above the stream beds, and a xeric
landscape dominated by an open pinyon–juniper woodland
above the canyon walls (Withers and Mead, 1993).
Bechan Cave is located in a semiarid tributary of the
Colorado River just north of the confluence with the Escalante
River in southern Utah. The cave, carved into the Navajo and
Kayenta sandstone formations, is a single large room approxi-
mately 53 m deep. Fortymile Canyon and Willow Gulch are
western tributaries of the Escalante River located less than
10 km west of Bechan Cave (Fig. 1). The numerous alcoves
within the two entrenched canyons are shallow yet long, with
high cliff overhangs.
Shrub-ox dung and diet
Dung morphology
Dung can be identified in several ways, including deter-
mining the morphological differences between whole dung
Table 1
Locations of Euceratherium remains in the Intermountain West
Location Deposit Remains Age Reference/Species
(1) Bechan Cave, UT Cave Tooth, dung 11,630± 150 yr* Mead and Agenbroad, 1992,E. collinum
(2) Cottonwood Alcove,
UT Site 42SA20858
Alcove Dung 12,510 ± 190 yr* Mead and Agenbroad, 1992,E. collinum
(3) Grobot Grotto,
40 Mile Canyon, UT
Alcove Dung 20,930 ± 400 yr*
18,320 ± 290 yr*
Mead and Agenbroad, 1992,E. collinum
(4) Hooper's Hollow,
40 Mile Canyon, UT
Alcove Dung 18,840 ± 350 yr
dated by assoc.
Mead and Agenbroad, 1992,E. collinum
(5) Oak Haven,
Willow Gulch, UT
Alcove Dung 9169 ± 100 yr to
11,690± 660 yr
dated by assoc.
Mead and Agenbroad, 1992,E. collinum
(6) Shrub-ox Alcove,
Willow Gulch, UT
Alcove Dung 12,690 ± 180 yr to
23,100 ± 660 yr
dated by assoc.
Mead and Agenbroad, 1992,E. collinum
(7) Eastern Grand Canyon Caves Cave –Late Pleistocene Mead et al., 2003 E. collinum
AZ; CB:8:1 CC:5:3 Phalanx calcaneus
(8) Rio Arriba County, NM Valley deposits Cranial fragment,
part horn core
Pleistocene Simpson, 1963 E. collinum
(9) Deadman Cave,
Pima County, AZ
Cave, pebbly silt Mandible with teeth 8000–12,000 yr BP Mead et al., 1984 E. collinum
(10) Anza Borrego
State Park, CA
Sands, muds,
silts and clays
No bones described 1.7–2.0 Ma Downs and White, 1968,
Opdyke et al., 1977 mentioned E. collinum
(11) Muskox Cave,
Eddy County, NM
Cave No bones described Pleistocene Logan, 1981 mentioned Preptoceras
sinclairi (Bush-ox)
(12) Burnet Cave,
Carlsbad, NM
Aeolian and
colluvial deposits
Cranium with horn cores,
palate with teeth, metacarpal,
1st and 2nd phalanx,
astragalus
Rancholabrean Shultz and Howard, 1935, assigned
to E. collinum morrisi and Preptoceras
sinclairi neomexicana
(13) Mineral Hill Cave,
Carlin, NV
Mixed gravel
and rocks
Phalange not mentioned McGuire, 1980 E. collinum
* = direct radiocarbon analysis.
144 M. Kropf et al. / Quaternary Research 67 (2007) 143–151
specimens, comparing dung pellet size and weight, and
utilizing dietary information in association with craniodental
morphology (Mead and Agenbroad, 1989). The type of graze
or browse consumed by herbivores typically determines dung
morphology (Mead and Agenbroad, 1989). For instance
Equus (horse), Mammuthus, and Nothrotheriops tend to pass
large fragments through their guts, forming large boluses (Fig.
2). Many ruminants such as Odocoileus (deer), Antilocapra
(pronghorn), Cervus (elk), Oreamnos (mountain goat), Ovis
(bighorn sheep), and Ovibos (musk-ox) tend to produce small
Figure 1. Map of the Colorado Plateau illustrating general locations of Euceratherium collinum sites in the Intermountain West. Numbered locations are listed in
Table 1.
Figure 2. Dung comparison: A, Nothrotheriops shastensis (GRCA 59620). B, Mammuthus (GLCA 382). C, modern Bison, dry diet (NAUQSP 7322). D, modern
Odocoileus (NAUQSP 6042). E, modern Equus (NAUQSP 6057). Photos by Sandra L. Swift.
145M. Kropf et al. / Quaternary Research 67 (2007) 143–151
dung pellets a centimeter or two in diameter (Fig. 3;Guthrie,
1992). Large bovids will produce large pellets or plates of
dung (Fig. 2), but with a high water content the dung forms an
amorphous mass (patty or cow pie) such as typical for Bison
(bison) and Bos (cattle). The HK pellets from the dry alcoves
are large cylindrically shaped pellets with a distinctive
‘Hershey's Kiss’type morphology (Fig. 3B). The pellets of
Ovibos moschatus and Bootherium (the extinct helmeted
muskoxen) tend to have a similar morphology, but the
Bootherium pellets (average diameter and length of
18.13 mm and 21.15 mm, respectively) are much larger.
Cervus elaphus produces a pellet that is generally similar in
size to the HK pellets, but more oval-shaped with both ends
rounded or tapered to a point. The HK morphology is
common in the six alcoves listed in Table 1 from the Colorado
Plateau and distinct from other known pellet-producing
artiodactyls.
Skeletal differences due to diet
All pellet-producing artiodactyls can be separated into three
feeding categories: browsers, grazers, and mixed feeders.
Species that feed predominantly on tree and shrub foliage
(≥90%) and eat ≤10% grass are considered browsers. Grazers
are defined as those species consuming at least 90% of their diet
as grass and ≤10% tree and shrub foliage. Mixed feeders are
those species that have between 10 and 90% grass in their diet
(Janis and Ehrhardt, 1988; Pérez-Barbería et al., 2001). Using
approximate measurements of the skull and dentary from
published material and photos taken of E. collinum specimens
at the Museum of Paleontology, University of California,
Berkeley, analysis of the craniodental morphology of E.
collinum can establish the animals’feeding category (Janis
and Ehrhardt, 1988; Janis, 1995; Solounias et al., 1995;
Mendoza et al., 2002).
Solounias et al. (1995) suggest that the best discriminator of
diet among extant ruminants is the presence of a prominence or
protuberance on the anterior part of the maxillary fossa (Figs. 4
and 5). The robustness of this protuberance varies in bovids due
to differences in the biomechanics of mastication. Among
grazers the masseter muscle, which originates from the
maxillary fossa, is generally larger than in browsers, because
of the tougher, more abrasive nature of their diet of grasses. The
connection for the larger masseter muscle produces a large
protuberance near the maxillary fossa (typically >3 mm;
Solounias et al., 1995;Fig. 5), while in browsers the
protuberance is small or barely visible (typically < 1 mm;
Solounias et al., 1995;Fig. 4). In mixed feeders the
protuberance is intermediate in size between grazers and
browsers. Examination of several maxillae of E. collinum
indicates the almost imperceptible sign of a protuberance near
the maxillary fossa—osteological evidence that E. collinum
was a browser and not a grazer or mixed feeder.
Additional analysis was preformed on craniodental vari-
ables involving hypsodonty index (the third lower molar tooth
height divided by the length of the second lower molar; Janis
and Ehrhardt, 1988), relative muzzle width (dividing the
premaxillary width by the palatal width; Janis and Ehrhardt,
Figure 3. Dung pellet comparison: A, modern Cervus (NAUQSP 6146). B,
Euceratherium collinum (GLCA 2788). C, modern Odocoileus (NAUQSP
6042). Photos by Sandra L. Swift.
Figure 4. Ventral view of Euceratherium collinum skull (Specimen 1009
Museum of Paleontology, University of California). Arrow designates slight
protuberance near the maxillary fossa.
Figure 5. Ventral and Dorsal view of Ovis canadensis skull-mixed feeder/grazer
(from Olsen, 1973 and modified. Reprinted courtesy of the Peabody Museum of
Archaeology and Ethnology, Harvard University). Arrow designates protuber-
ance near the maxillary fossa.
146 M. Kropf et al. / Quaternary Research 67 (2007) 143–151
1988), and relative length of the premolar tooth row (length of
the lower premolar row compared to the lower molar row;
Mendoza et al., 2002). The craniodental variables for bovids
appear to have significant overlap between browsers and mixed
feeders, but significant distinction occurs between grazers and
all other feeding types. For two of the craniodental variables,
E. collinum falls within the mean for mixed feeders, but for
the relative length of the premolar tooth row the E. collinum
value tended to be closer to browsers. Because of the abrasive
nature of grasses, the hypsodonty index for grazers is almost
always higher than for browsers or mixed feeders and has
always been considered a good indicator of diet, but Janis
(1988) states that animal habitat may be more important in
determining the degree of hypsodonty than dietary preference.
Ungulates preferring open habitats and ground-level vegetation
tend to be more hypsodont, because of grit accumulation on
plant material. In summary, E. collinum shared similarities
with browsers and mixed feeders in relative muzzle width and
hypsodonty index, but it was more similar to browsers in
relative length of the premolar tooth row. E. collinum was
clearly not a grazer.
Dung and diet
Large remains of plants can be easily recognized in the
boluses of Mammuthus and Nothrotheriops shastensis; how-
ever, identifying plant macrofossils is much more difficult in
pellet-producing ruminants. Ruminants tend to chew all their
food into finer components (Mead and Agenbroad, 1989).
Therefore, in order to place the HK dung pellets into a definitive
dietary classification, a detailed analysis using techniques of
microhistology and palynology was utilized to determine diet
and paleoenvironment.
Microhistology is the study of microfossil plant remains,
consisting of insoluble parts such as phytoliths and cuticles
that have traveled through and survived the digestive track of
the animal. Research in general has shown that a good
relationship exists between the plants consumed and the plant
microfossils excreted as dung, but there is potential for error
due to some plant species, such as forbs, not surviving
digestion (Sparks and Malechek, 1968; Todd and Hansen,
1973; Gardner et al., 1993). Pollen is able to survive most
environmental degradation and digestion. Analysis of pollen
from dung can help recreate a more regional picture of the
paleoenvironment (Bradley, 1999). However, pollen from
dung may not be representative of the diet of the animal,
because the animal may ingest it directly through the
consumption of a flower, or indirectly, if the pollen settled
or attached to the leaves of the plants in its diet (Thompson et
al., 1980; Mead et al., 1986b; Davis and Anderson, 1987).
Few studies of the dung of animals living today have shown a
high correlation between the plant species consumed and the
pollen present in the dung (Mead et al., 1987). However,
pollen can help designate the time of year plants were
consumed (Thompson et al., 1980; O'Rourke and Mead, 1985;
Mead et al., 1987).
It is immediately apparent from the preliminary results of
the microhistology data in Table 2 that the HK pellets are
from a browser, with ≥95% of each pellet consisting of tree
or shrub foliage and ≤5% grass. In contrast, the diet of O.
harringtoni was varied and consisted of grasses, sedges,
shrubs, and conifer trees (a mixed feeder), while Mammuthus
and Bison dung consisted predominantly of grasses and sedges
(grazers; see Tables 2, 3, and 5 in Mead and Agenbroad,
1989). Could the restrictive dietary results from the HK pellets
be a result of food availability? This is unlikely, because we
know from analysis of Mammuthus and Bison dung, in the
same stratigraphic unit as Euceratherium in Bechan Cave, that
grasses and sedges were present and available in the region,
yet the producer of the HK pellets did not consume these
plants. The diet suggested by the microhistological data
indicates a non-grazer, and since E. collinum was the only
non-grazer whose skeletal remains were found at Bechan
Cave, we conclude that the HK pellets were produced by E.
collinum.
The main dietary components recovered from the E. collinum
HK pellets included Artemisia tridentata,Acacia sp., Oe-
nothera sp. (evening primrose), Quercus,Rhus sp. (sumac), and
Chrysothamnus sp. (Table 2—includes the microhistological
results for E .collinum HK pellets 1 thru 12 and pollen analysis
for pellets 6, 7, and 12). In pellets 6 and 7, Artemisia pollen was
found in association with plant fragments of Chrysothamnus and
Quercus. As previously mentioned, pollen can designate the
time of year plants identified in the pellet were consumed. The
presence of abundant Artemisia pollen (70% to 87%) in the two
pellets suggest the browse plants, Chrysothamnus and Quercus,
were consumed during the fall when Artemisia generally
blooms. A large percentage of spring pollen (78%) from either
Amelanchier (serviceberry) or Quercus was recovered from
pellet 12. It suggests the predominant browse, Acacia, was
consumed during the spring when Amelanchier and Quercus
typically bloom. Our investigation into the dietary habits of E.
collinum indicates a change in the dominant browse consumed
from spring to fall and suggests E. collinum had a year-round
presence in the region.
Dung morphometrics
In addition to dietary evidence, the sizes, weight, length, and
diameter of dung pellets from a variety of extinct and extant
artiodactyl species (Antilocapra americana,Cervus elaphus,
Odocoileus spp., Oreamnos americanus,Oreamnos harring-
toni,Ovis canadensis,Bootherium, and Lama (llama)), were
compared to the HK pellets. The dried fecal material was
weighed using a triple beam balance and measured using
electronic digital calipers. Length of fecal pellets was measured
along a line parallel to the direction the dung was expelled,
which is the direction of taper typically exhibited by one end of
the pellet. Alces alces (moose), Camelops (extinct camel), and
their ancestors were not included in this analysis, because of
their much larger size (Mead et al., 1986c). However, Lama was
included because of the similarity in fecal pellet size and
because several sites containing extinct fossil llama (Hemiau-
chenia and Palaeolama) occur in close proximity to the Colorado
Plateau (Kurtén and Anderson, 1980; Harris, 1985). All fossil and
modern dung samples were curated at the Laboratory of
147M. Kropf et al. / Quaternary Research 67 (2007) 143–151
Quaternary Paleontology, Northern Arizona University, where
comparative materials include extant and confirmed extinct
species.
Ninety-four complete pellets of the distinctive HK shape
were analyzed in our study. Comparative samples of modern A.
americana and extinct Bootherium were fewer in number. The
smaller sample of specimens for these mammals does not
seriously affect the outcome of this analysis; they were included
only to show the wide morphological variability between
specimens. Simple statistical analysis was used to determine
means and standard deviations between dung weight and size
within individual species (Table 3). The results of individual
measurements of dung pellets from nine species of artiodactyls
are shown in Figures 6 and 7. Some similarities were noted
between three artiodactyl species: Lama,Bootherium,C.
elaphus, and the HK pellets.
The following results were obtained after testing for
significant differences between HK pellets and Lama,
Bootherium, and C. elaphus pellets. Diameters and weights
of HK pellets were significantly different (p < 0.05) from the
diameters and weights of Lama,Bootherium, and C. elaphus
pellets. HK pellets are significantly different (p < 0.05) in
length from Lama and Bootherium pellets; however, C.
elaphus pellets did not test significantly longer or shorter
(p > 0.05) in lengt h.
Discussion and conclusions: the natural history of
Euceratherium collinum
Previously confirmed identities of extinct herbivore dung
from the dry alcoves and caves of the Colorado Plateau include
Bison,Mammuthus,Nothrotheriops, and Oreamnos harringtoni.
Table 3
Dung measurements
O. americanus O. canadensis O. hemionus
Dia. Lt. Wt. Dia. Lt. Wt. Dia. Lt. Wt.
Mean 8.71 12.16 0.22 8.82 13.86 0.25 9.00 12.84 0.32
Stdev 1.28 2.04 0.06 0.87 1.77 0.06 1.54 2.37 0.17
C. elaphus HK pellets Lama
Dia. Lt. Wt. Dia. Lt. Wt. Dia. Lt. Wt.
Mean 13.97 19.46 0.70 14.54 19.25 1.06 10.25 17.29 0.41
Stdev 1.72 2.73 0.31 2.01 2.59 0.21 1.21 2.73 0.12
O. harringtoni Bootherium A. americana
Dia. Lt. Wt. Dia. Lt. Wt. Dia. Lt. Wt.
Mean 11.47 15.59 0.43 18.13 21.15 1.45 9.43 11.56 0.19
Stdev 0.93 1.98 0.09 0.98 1.60 0.20 0.62 2.08 0.03
Dia. = diameter, Lt. = length, Wt. = weight, Stdev = Standard deviation.
Table 2
Percent relative density of plant fragments and pollen for 12 E. collinum HK pellets
Microhistological analysis was performed on all 12 dung pellet samples. Pollen analysis was only performed on dung pellets 6, 7, and 12. Abbreviations: m,
microhistology sample: p, pollen sample (in shaded columns).
148 M. Kropf et al. / Quaternary Research 67 (2007) 143–151
Here we provide evidence confirming the identity of the dung
of yet another extinct herbivore, Euceratherium collinum, that
produced dung pellets with a distinctive morphology that are
typically larger in size than pellets of other artiodactyl species
presently known from the Colorado Plateau (i.e. C. elaphus,
Ovis, and Odocoileus). The HK pellets were also found in
association with E. collinum skeletal material, the only skeletal
remains of a large mammal recovered at Bechan Cave. Analysis
of the craniodental morphology and microhistology has
provided correlative evidence that E. collinum was the most
likely producer of the HK dung pellets. The HK dung
specimens from Bechan Cave were collected from a late
Pleistocene stratigraphic unit dating from 14,700 to 11,000
14
C
yr BP (Mead et al., 1986a). There is no confirmed skeletal
evidence of C. elaphus,O. americanus, or llama (various
extinct forms) recorded on the Colorado Plateau from the late
Pleistocene. C. elaphus fossil remains have been found as near
as New Mexico, Texas, and Oklahoma, but are more common
east and north of Missouri (Kurtén and Anderson, 1980;
Thomas and Toweill, 1982; Harris, 1985). Fossil sites contain-
ing late Pleistocene remains of Hemiauchenia have been
located no closer than southeastern Arizona and the Albuquer-
que Basin (Lindsay, 1978; Morgan and Lucas, 2000). O.
americanus remains have not been found any farther south than
Idaho and northern Wyoming (Mead and Lawler, 1994).
Ever since Eames’(1930) description of plant macrofossils
in dung of extinct Nothrotheriops shastensis, the use of
Pleistocene dung has been important in recreating the
paleoecology of the American Southwest. Previous studies of
Pleistocene dung from the Colorado Plateau have provided
good data on the diets and paleoenvironments of extinct N.
shastensis,Oreamnos harringtoni, and Mammuthus. From the
Bechan Cave dung, Mead and Agenbroad (1989) investigated
the dietary history of two extinct species, N. shastensis and
Mammuthus. The two dominant dietary components included
grasses and sedges, with other plant remains consisting of
Atriplex (saltbush), Artemisia tridentata,Betula occidentalis
(water birch), Picea pungens (blue spruce) and cactus (Mead et
al., 1986a; Mead and Agenbroad, 1989).
Although Artemisia tridentata and Quercus sp. are well
represented in the diet of E. collinum and as pollen in the dung
layer of Bechan Cave, both are now uncommon near the cave.
Quercus is typically found in cooler microenvironments in
canyons where moisture is readily available year round. Withers
and Mead (1993) interpret the gradual disappearance of Quer-
cus gambelii within Fortymile Canyon as indicating a period of
increasingly warmer climate with less precipitation. Artemisia
tridentata also prefers cooler and more mesic conditions and
therefore is not as common today in the canyons.
In summary, E. collinum was a year-round browser in the
Escalante River Basin where the open, steppe-type paleoenvir-
onment was dominated by grasses, sagebrush, and oaks.
Evidence of Betula occidentalis and Picea pungens at Bechan
Cave does suggest that, at minimum, an open boreal forest
occurred in close proximity to the canyon habitat of E.
collinum. However, there is no evidence E. collinum browsed
these plants, indicating the animal restricted its diet to the
steppe-type plants along the edges of the forests. Previous local
plant and dietary research, along with data supplied by E.
collinum HK pellets, indicates cooler and more mesic condi-
tions. However, the environment inhabited by E. collinum
changed during the Pleistocene/Holocene transition, with
warmer and dryer conditions forcing a reorganization of the
local plant community. Sub-alpine trees moved to higher
elevations, while Quercus and Artemisia became less common
and retreated to cooler habitats with more available moisture
within the canyons (Withers and Mead, 1993; Anderson et al.,
2000). Even though the local environment underwent signifi-
cant change during the Holocene, the extinction of E. collinum
within the Escalante River Basin is puzzling, because appro-
priate environments containing several of its favorite foods,
sagebrush and oaks, are still present within the canyons or in
nearby plateaus and mountains. Analysis of the dung contents
has yet to address the carrying capacity of local environments.
This aspect of changing environments has not been a focus in
relation to the late Pleistocene extinction event/process.
Figure 7. Bar graph comparing weight of dung pellets. Kilograms in parentheses
are average body weights of adult male ruminants. Error bars illustrate one
standard deviation.
Figure 6. Bar graph comparing diameter and length of dung pellets. Kilograms
in parentheses are average body weights of adult male ruminants. Error bars
illustrate one standard deviation.
149M. Kropf et al. / Quaternary Research 67 (2007) 143–151
Acknowledgments
We thank the National Park Service and staff at Glen Canyon
National Recreation Area for their permits and support in the
1980s during the initial investigations into late Pleistocene
remains in Willow Canyon, Fortymile Canyon, and Bechan
Cave. Thanks also to the Museum of Paleontology at the
University of California, Berkeley, for access to their fossil
vertebrate collections; and to Susan Hall for editorial assistance.
We thank the following for continued help on the fossils curated
in the National Park Service Repository and studies of dry caves
of the Colorado Plateau: Mary C. Carpenter, Larry C. Coats,
Sandra L. Swift, Larry D. Agenbroad, Ken L. Cole, and Marci
Hollenshead. Laboratory of Paleoecology Contribution Number
99.
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