Download using mortality profiles to infer behavior in the

Journal of Mammalogy, 84(2):418–430, 2003
USING MORTALITY PROFILES TO INFER BEHAVIOR IN THE
FOSSIL RECORD
TERESA E. STEELE*
Department of Anthropological Sciences, 450 Serra Mall, Building 360, Stanford University,
Stanford, CA 94305-2117, USA
Mortality profiles can be used to investigate modes of accumulation of fossil assemblages,
including predation by ancient nonhuman and human (Homo) hunters. Prey age at death
reflects hunting decisions and opportunities in terms of calories returned for energy spent
and risks taken. Nonhuman carnivores commonly harvest vulnerable individuals (young
and old), whereas humans consistently can take prime adults. As an example of how mortality profiles can be used to illuminate predator behavior, this article examines when the
ability to select prime-age animals emerged during human behavioral evolution. Although
it would be expected that the appearance of this behavior coincided with the appearance
of morphologically and archaeologically modern humans, analyses of archaeological assemblages from western Europe and South Africa suggest that this trait was already present
in archaic people who preceded modern humans. Studying age distributions in fossil assemblages is not without its limitations, including the difficulty of estimating age at death
in fossil specimens, pre- and postdepositional biases, and reconstructing the age structure
and behavior of prey herds. Nevertheless, valuable behavioral information can be gained
by using controlled comparisons of many assemblages.
Key words: age–structure analysis, Canis lupus, Cervus elaphus, elk, human evolution, hunting
strategies, mortality profiles, predation, wolves
Hunters, both human (Homo) and nonhuman, make decisions about which prey to
pursue by considering which individuals
will provide the highest return rate, usually
calories, per unit of time or energy spent
foraging (Stephens and Krebs 1986). In addition to calories, predators may also consider risks involved in hunting, such as the
possibility of spending too much time for
energy return in searching for prey, the likelihood that prey will injure hunters, and for
humans, the number of hunting implements
that might be lost (Frison 1991). Consequently, prey that hunters capture provides
information on hunting strategy and prey
choice.
In species where males are larger than
females, prime males will provide the most
calories of any age or sex group; however,
risks to the hunter may make males unobtainable or less attractive. These risks may
dictate the targeting of more vulnerable individuals, such as the diseased, injured, senile, or young. Consequently, data on age
at death provide information about how
readily a hunter can take the strongest, or
prime, animals versus the weakest or most
vulnerable individuals, usually the young
and old. A hunter of prime animals must be
either stronger or faster than the prey or
skilled enough (meaning technologically
sophisticated for humans) to reduce risks of
injury and increase the probability that the
animal will be taken. Because of these
trade-offs, analyses of ages-at-death distributions, or mortality profiles, and prey in
fossil assemblages can provide information
on predator behavior.
* Correspondent: [email protected]
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SPECIAL FEATURE—MAMMALIAN PALEONTOLOGY
Analyses of mortality profiles found in
archaeological assemblages potentially can
provide information on human behavioral
evolution, because of differences in the way
that humans and other nonhuman predators
select prey. Humans are unique in consistently selecting prime-age prey, and therefore, identifying when humans first developed this ability could signal significant
changes in human language ability, cognitive function, or cultural capacity. Modern
humans (Homo sapiens) dispersed from Africa approximately 40,000–50,000 years
ago and are associated with the Upper Paleolithic, which is characterized in the archaeological record by having more numerous sites, more intensely occupied sites,
standardized but diverse tools, tools made
out of bone and ivory, art objects, and items
of personal adornment (Klein 1999). It is
reasonable to expect that the ability to consistently hunt prime animals also emerged
40,000–50,000 years ago.
MATERIALS
AND
METHODS
Numerous methods exist for assessing age at
death of skeletal specimens (for reviews see
Amorosi 1989; Morris 1972; Pike-Tay 2000;
Wilson et al. 1982); analyses of epiphyseal fusion and tooth eruption are most commonly used
(Klein and Cruz-Uribe 1984; O’Connor 2000;
Reitz and Wing 1999). Age at death can be estimated from teeth using wear stages (e.g.,
Brown and Chapman 1991b; Lowe 1967; Quimby and Gaab 1957), eruption stages (e.g., Brown
and Chapman 1991a), the quadratic–crownheight method (e.g., Klein et al. 1983; Pike-Tay
et al. 2000; Spinage 1972), regression equations
based on known-age samples (e.g., Klein et al.
1983; Morrison and Whitridge 1997), or cementum annuli data (e.g., Hamlin et al. 2000; Keiss
1969; Mitchell 1967; Pike-Tay 1991; Spinage
1973).
Tooth-wear rates may vary between individuals and populations, possibly because of differences in diet (Flook 1970; Hewison et al. 1999;
Skogland 1988) or degree of enamel mineralization (Kierdorf and Becher 1997). Visual assessments of wear can be subject to interobserver variation (Hamlin et al. 2000; Keiss 1969;
Van Deelen et al. 2000), but the quadratic–
419
crown-height method minimizes this by metrically assessing wear (Steele 2002). Paleobiologists are most interested in the overall shape of
a profile, so if there is no systematic bias in age
estimations and if age classes are broad, eruption
and wear methods should be sufficient. The cementum annuli method is of limited use to archaeologists because of the time, expertise, and
equipment involved; because it is frequently applied to incisors in recent specimens, which are
often unidentifiable to species and damaged in
fossil assemblages; because large samples are
necessary to reconstruct a mortality profile accurately; and because most archaeologists are reluctant to destroy irreplaceable fossils (Hamlin
et al. 2000; Klein and Cruz-Uribe 1984; PikeTay 1991).
To create mortality profiles, age estimates are
compiled into histograms or line graphs that
show the proportion (either frequency or percentage) of individuals that died in each age
class. Age classes are defined depending on precision of age estimation, life histories of species
under study, and questions under investigation.
For large mammals, age classes commonly are
1 year or groups of years, such as 10% of life
span, but any consistent, easily definable, and
replicable age classes are suitable. The Kolmogorov–Smirnov test is used to compare the cumulative frequency distributions of 2 histograms
(Klein and Cruz-Uribe 1984; Sokal and Rohlf
1995). In species where it is difficult to estimate
age at death, raw measurements of tooth crown
heights can be compared directly by creating
box plots that include 95% confidence interval
around sample medians (Klein and Cruz-Uribe
1996; Klein et al. 1999). In some species where
body size, and therefore tooth size, differs
through time and across space, crown heights
can be standardized.
Following Kurtén (1953), Van Valen (1964),
and Voorhies (1969), paleobiologists use 2 models of idealized mortality profiles, called catastrophic and attritional, to help interpret age distributions found in assemblages. The idealized
mortality profiles that I use are from Klein
(1982) and are based on a hypothetical population of large mammals that is stationary (size,
survival, and fecundity are not changing) and in
which females have synchronized birth of 1 offspring/year (Fig. 1). Although variations may
occur depending on local conditions or life-history differences such as twinning, the shape of
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Vol. 84, No. 2
FIG. 1.—Idealized catastrophic (left) and attritional (right) mortality profiles for a population of
large mammals that gives birth to 1 offspring/year and is not changing in size. Dark bars refer to
the number of individuals in each age class in a living herd. Hatched bars represent the number of
individuals that died between each age class, the attrition on the herd. Hatched bars correspond
directly between the 2 histograms. These idealized profiles provide guidelines for comparisons of
mortality profiles identified in faunal assemblages. Data from Klein (1982) and Voorhies (1969).
these models (i.e., patterns of age-specific mortality) is generally consistent across taxa with
similar life histories (Caughley 1966, 1977). The
idealized catastrophic profile shows that in a living population, young animals are most abundant and the next age group contains fewer individuals because of high calf mortality. Each
subsequent age class has fewer individuals until
none remain. This model is called ‘‘catastrophic’’ because it represents the mortality profile
that would be found if a stationary herd died at
once, shortly after the season’s births (Caughley
1966, 1977; Deevey 1947; Klein 1982).
The idealized attritional profile shows the
number of individuals that died between each
age class to produce the idealized catastrophic
profile, and therefore, it is a mathematical derivative of the catastrophic profile. These deaths,
caused by disease, malnutrition, and nonhuman
predators, are the natural attrition on a herd. This
model also has a high number of juvenile individuals, but much fewer adults, although they
are still present. Higher mortality in old individuals sometimes produces a rise in the number of
individuals in older age classes; thus, the attritional profile sometimes is described as ‘‘Ushaped’’ or ‘‘J-shaped’’ (Caughley 1966; Klein
1982; Levine 1983; Stiner 1990).
In a fossil assemblage, an age profile that resembles a living herd might indicate 1 of 4 sit-
uations. In a synchronic sample, where all bones
are deposited at once, the assemblage might be
the result of 1) a natural catastrophe, such as a
flood, volcano, or blizzard (Lubinski 2001;
Voorhies 1969); or 2) hunters driving an entire
herd either into a trap or surround or over a cliff
(Frison 1978; Nimmo 1971). In a diachronic assemblage, where bones are accumulated a few
at a time, a similar mortality profile might be
created by people 3) hunting individual animals,
where prey are obtained in proportion to their
presence in the herd; or 4) or setting individual
traps that are equally successful in trapping animals of all ages. When an age profile that resembles the attritional model is reconstructed in
a fossil assemblage, it could represent hunting
of the most vulnerable individuals of the herd or
scavenging, because scavengers would be eating
carcasses produced by attritional factors (Klein
1982, 1994). The idealized catastrophic and attritional profiles are not the only possible age
distributions that might be found, and much variation exists in archaeological and paleontological sites. However, these models still provide
useful guidelines for interpreting faunal assemblages.
Prey availability influences predator choice,
and ungulate herds often change locations and
sexually segregate, depending on season (Bleich
et al. 1997; Bowyer 1984; Geist 1982; Kie and
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Bowyer 1999). High harvest pressure will skew
a herd’s age distribution toward younger individuals (Koike and Ohtaishi 1985; McCullough
1979). These changes potentially could influence
age profiles of harvested prey. Unfortunately, it
is quite difficult to reconstruct prey abundance
at specific sites when looking tens of thousands
of years into the past, because this would require
fundamental assumptions about geomorphology,
habitat, and climate, all of which are difficult to
reconstruct on such a fine scale. These assumptions are as equally presumptuous as the assumption that the prey population is stationary,
although some progress has been made in reconstructing available sex ratios (Berger et al.
2001). Fortunately, in both the archaeological
and the paleontological record, time averaging
is often the rule (Hadly 1999). Seasonal fluctuations in age structure of the prey species will
be averaged out during the course of the year,
or if the site was occupied in only 1 season, will
be averaged over many years. Fluctuations in
age structure over decades or centuries also will
be averaged in the prehistorical record, allowing
researchers to identify ‘‘typical’’ hunting strategies rather than individual hunting strategies.
Fortunately, this is the level of analysis that
helps answer paleoecological questions.
Prey choice also is influenced by factors other
than caloric returns, including chance. Hunters
may choose a species because it is more amenable to being herded or driven. Human hunters
may choose their prey based on hide quality,
which also changes with age or season (e.g.,
McCabe 1982). Humans may choose to target 1
sex, such as male cervids, because they desire
antlers for tools or trophies or canines for ornaments (e.g., d’Errico and Vanhaeren 2002; K.
Hamlin, pers. comm.; Pitts 1979). These factors
will influence age distributions found in fossil
assemblages and can be investigated further as
explanations for deviations from the idealized
profiles.
Once an animal has been harvested, different
aged prey may be handled differently, which
will affect resulting mortality profiles (Bartram
1993; Bunn 1993; Marean 1997). For example,
skulls of adults may be left at the kill site and
not returned to camp because they are too heavy,
or only skulls of adult male deer may be transported to the campsite or worksite for antler processing. Large mandibles may be broken up for
marrow processing, whereas smaller ones re-
421
main whole. Juveniles are more likely to be fully
consumed by predators or subsequent scavengers because of their small size and more cartilaginous bones. Thus, juveniles are often underrepresented in faunal assemblages (Binford and
Bertram 1977; Blumenschine 1987; Munson
2000). Once material has been deposited in a
site, postdepositional destruction will affect
large and small (including juveniles of large species) specimens differently (Klein and Cruz-Uribe 1984; Levine 1983; Lyman 1994). This destruction of juvenile remains limits our ability to
distinguish hunting focusing on prime adults
from that resembling the idealized catastrophic
profile.
To help control for these limitations, as many
age determination methods as feasible should be
applied to a fossil assemblage, and mortality
profiles should be constructed in multiple ways,
such as histograms of estimated ages and box
plots comparing raw crown heights. If the results
are concordant, then the faunal analyst can be
more confident about the mortality profile. Many
samples should be compared to see if a robust
pattern appears. Additionally, comparing samples with similar postdepositional histories will
help control for some biases. Surface qualities
of bone and relative abundance of more and less
dense postcranial parts can be recorded to elucidate potential differences due to postdeposition destruction. The ratio of isolated teeth to
complete mandibles also may provide an indicator of postdepositional destruction. At the
least, mortality profiles should be compared with
juveniles included and excluded, although some
researchers have proposed correction factors to
account for biases against juvenile remains (Ducos 2000; Levine 1983; Marean 1997; Munson
1991).
HUMAN
AND
CARNIVORE HUNTING
Because the mode of accumulation is
known, an example using modern data
demonstrates how mortality profiles can be
used to infer predator behavior and generate
hypotheses for further testing. I reconstructed mortality profiles for 2 samples of Rocky
Mountain elk (Cervus elaphus nelsoni)
from Wyoming and Montana (Fig. 2). One
sample is composed of 98 mandibles of elk
killed by wolves (Canis lupus) that were
collected by Yellowstone National Park bi-
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Vol. 84, No. 2
FIG. 2.—Mortality profiles of Rocky Mountain elk (Cervus elaphus nelsoni) hunted by wolves
(Canis lupus; top) and recent humans (Homo sapiens; bottom). Ages for the samples are based on
quadratic–crown-height method of estimating age at death from tooth crown heights using dp4 and
m1 (see Klein et al. 1983 for more details and formulas). Box plots compare median m1 crown
heights for the 2 samples (see Klein and Cruz-Uribe 1996 for discussion of box plots). In both
analyses, the 2 samples are significantly different (drawings courtesy of R. Klein).
ologists in 1999, primarily from January to
May and from October to November. Many
remains of calves were badly damaged or
fully consumed before park biologists could
collect mandibles, so the wolf-kill sample
is biased against juveniles (D. Smith, pers.
comm.). The other sample consists of 226
mandibles collected from hunter checkpoints in Montana, north of Yellowstone
National Park (Hamlin et al. 2000; Quimby
and Gaab 1957; C. Wolf collected some
data with this sample). I estimated age at
death using a method suitable to fossil assemblages—applying the quadratic–crownheight method to dp4 and m1 (Klein and
Cruz-Uribe 1984; Klein et al. 1983). I generated histograms with 10% of life-span age
classes and considered 21 years to be the
potential maximum longevity of individuals
from this population (Houston 1982).
The wolf-harvested profile is distinct
from the idealized catastrophic profile and
closely resembles the idealized attritional
profile except for the high number of individuals in the oldest age class (19–21 years)
in the wolf-kill profile. To further investigate this discrepancy, I offer 3 hypotheses.
First, the over-abundance of old individuals
is an artifact of the method used to assign
age at death because all individuals with
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SPECIAL FEATURE—MAMMALIAN PALEONTOLOGY
teeth completely worn away were assigned
to the oldest age class. Second, because of
the ease of tracking wolves in snow, the
wolf-kill sample was collected primarily in
winter before young are born in June. The
large number of old individuals could represent the easiest winter prey, and other age
groups could be targeted at other times of
the year. Third, wolves were reintroduced
into Yellowstone after an absence of 60
years (Smith et al. 1999). During that time,
grizzly bears (Ursus arctos) were the primary predator of elk, but bears killed mainly newborns (Knight et al. 1999; Singer and
Mack 1999). If elk population size was increasing during this time, low predation on
adults could have allowed an increase in
abundance of old elk to beyond what is expected in the model.
The human-harvested profile is similar to
the idealized catastrophic profile and different from the idealized attritional profile.
Human hunters took more individuals in
age classes 2 and 3 (2–6 years) than in the
catastrophic profile. I hypothesize that 1)
hunters preferred the younger adults because of their larger size relative to juveniles, but the inexperience of young adults
compared with prime adults made them
easier to take; 2) due to heavy hunting for
antlers, there could be a limited number of
older males available in the prime age classes (K. Hamlin, pers. comm.), and therefore, humans were hunting the next best
antler carriers: younger adult males, along
with females of any age class; or 3) seasonal hunting regulations imposed by Montana Fish, Wildlife, and Parks dictated the
ages of the hunted animals and not hunters’
preference.
Mortality profiles for wolf- and humanharvested elk are significantly different
when complete profiles are compared (Kolmogorov–Smirnov [K-S], z 5 2.375, P ,
0.001). Because the wolf-harvested sample
is biased against juveniles, I also compared
only adults in the samples. The significant
difference remains (K-S, z 5 3.581, P ,
0.001). Box plots of the wolf- and human-
423
harvested samples also indicate that wolves
were hunting older elk than were humans
(Fig. 2). The wolf versus human example
shows that humans are more likely to kill
adult elk, whereas wolves are more likely
to take vulnerable (youngest and oldest)
members of the herd. This is not to say that
nonhuman predators never hunt prime ungulates; it is well documented that they can
take adult animals (Gasaway et al. 1983,
1992; Mech et al. 2001; this study), but
they do not harvest them as frequently as
do humans (Boyd et al. 1994; Carbyn 1983;
Kunkel et al. 1999). Variation is found in
this pattern because many local factors influence what ages are harvested at a particular time, such as the age structure of the
available herd, predator and prey density, or
climatic conditions (Boyd et al. 1994;
McCullough 1979; Mech et al. 2001; Van
Ballenberghe and Ballard 1997).
Klein (1982) also reported a distinction
between human and nonhuman hunting
when comparing Burchell’s zebra (Equus
burchelli) and Cape buffalo (Syncerus caffer) killed by African lions (Panthera leo)
in the Serengeti Plains with chamois (Rupicapra rupicapra) killed by modern hunters
in the Alps and pronghorn (Antilocapra
americana) killed by prehistoric Native
Americans in Wyoming. Additionally, comparative data on modern predators assembled by Stiner (1990) indicate that only humans can consistently and exclusively hunt
prime animals. McCullough (1979) compared published ages of white-tailed deer
(Odocoileus virginianus) harvested by prehistoric hunters in eastern North America
with ages of deer killed by wolves in his
study area in southern Michigan. The humans harvested more prime adults, whereas
the wolves took more juveniles and old individuals.
PREHISTORIC HUMAN HUNTING
The idealized catastrophic profile assumes that predators are capable of selecting randomly from prey herds, i.e., they are
able to harvest all age classes equally. In
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JOURNAL OF MAMMALOGY
reality, skill determines in part which prey
actually will be harvested. Modern humans
lie at an extreme, because they can focus
their hunting on prime-age animals. Below,
I use mortality profiles from fossil assemblages to investigate the emergence of this
behavior.
Acheulean.—The Acheulean stone tool
industry began in Africa 1.7–1.5 3 106
years ago, was present in Europe 500,000
years ago, lasted in both places until about
200,000–250,000 years ago, and is associated with H. ergaster or H. erectus (Klein
1999, 2000b). This tool industry is characterized by large hand axes and a variety
of flake tools. There is no evidence of bows
and arrows or spear throwers during this
time, although wooden spears have been
found (Thieme 1997). Acheulean stone
tools commonly occur near animal bones
on ancient land surfaces, but a functional
relationship between them cannot be assumed. These sites are mainly open-air localities near ancient streams or ponds that
would have naturally attracted humans and
animals (Klein 2000b). The bones could
represent human kills, or they could be natural deaths or carnivore kills that were either left alone or scavenged by other carnivores, including humans.
For example, at the site of Duinefontein,
South Africa, animal bones and stone tools
accumulated around marshy dune swales
200,000–400,000 years ago (Klein et al.
1999). Giant buffalo (Pelorovis antiquus)
from the site follows an attritional pattern
with many old animals and only a few juveniles. Black wildebeest (Connochates
gnou) also is represented by only a few juveniles, but many young adults (about 2
years old) also are present. Continuing excavations have increased the sample and
confirmed these patterns (R. Klein, pers.
comm.). Brown hyenas (Hyaena brunnea)
do not hunt animals the size of black wildebeest, but carnivore marks greatly outnumber stone tool marks on all bones, making the cause of mortality inconclusive
(Klein et al. 1999). Humans may have had
Vol. 84, No. 2
little involvement with the animal remains;
they could have hunted the animals, or they
could have scavenged the remains of natural deaths or other carnivoran kills.
Isolating the role of humans in Acheulean sites is difficult, and carnivore involvement in the form of chew marks and fossilized feces is often obvious (Gaudzinski
and Turner 1996; Klein 2000b). Frequently,
samples are too small to create informative
mortality profiles. True occupation sites
would be useful, such as those in caves, although such sites may not exist for this time
period. However, the collective literature on
Acheulean assemblages suggests that these
early humans were unable to regularly hunt
prime-age prey.
Middle Stone Age (Africa) and Middle
Paleolithic (Europe).—The Middle Stone
Age followed the Acheulean in Africa
spanning from 200,000–250,000 years ago
to about 50,000 years ago and is associated
with H. helmei, which is also referred to as
archaic H. sapiens (Klein 1999, 2000a).
The Middle Paleolithic followed the Acheulean in Europe, persisted until about 35,000
years ago, and is associated with H. neanderthalensis, the Neanderthals (Klein 1999,
2000a). The stone tool industries for these
2 groups are very similar and are also similar to flake tools found in Acheulean assemblages; there is no evidence of bows
and arrows or spear throwers during this
time (Klein 1999). It does appear that stone
points were mounted onto wooden shafts,
possibly to be used as thrusting spears
(Shea 1989, 1998; Shea et al. 2001).
Klasies River Mouth cave I, South Africa
(74,000–128,000 years ago) provides an
example of how an early human group
hunted different species with different strategies (Klein 1978, 1994; Klein and CruzUribe 1996). Mortality profiles of Cape buffalo from this site reflect the idealized attritional profile (Fig. 3). The abundance of
juveniles suggests that Middle Stone Age
people hunted buffalo and did not scavenge
off the natural attrition of the herd, because
other carnivores are likely to consume ju-
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425
FIG. 3.—Mortality profiles of eland (Taurotragus oryx) and Cape buffalo (Syncerus caffer) from
the Middle Stone Age site of Klasies River Mouth, South Africa. When hunting buffalo, Klasies
people primarily took young and old (most vulnerable) individuals of this large and dangerous species. They were able to regularly hunt prime-age eland, potentially by driving them. Data from Klein
(1994; drawings courtesy of R. Klein).
venile carcasses quickly and completely, as
is apparent in the wolf-kill sample presented here. Nonetheless, Klasies people were
able to take only young and old individuals,
presumably because buffaloes were large
and dangerous and Middle Stone Age people lacked projectile technology. In contrast, eland (Taurotragus oryx) from this
site produces a mortality profile that is very
similar to the catastrophic model, indicating
that early people were able to take individuals of all ages of this species. Klein et al.
(1999) suggested that this relatively docile
species was driven either over cliffs or into
blind traps. Other Middle Stone Age sites
in South Africa also show this pattern of
age structure for eland (Klein and Cruz-Uribe 1984, 1996), and historic observations
indicate that this species was amenable to
driving (Klein and Cruz-Uribe 1991). This
example shows how attributes of prey behavior (and other attributes such as body
size) directly affect hunting strategies, so
these attributes must always be considered
when interpreting mortality profiles.
Early humans from similar time periods
and with similar tool technology may have
used different strategies to hunt the same
species. Paleolithic people in southwestern
Europe frequently hunted red deer (Cervus
elaphus) when it was available. Four Middle Paleolithic assemblages show variation
in red deer age structures (Fig. 4). Lazaret
(130,000–170,000 years ago) is from Nice,
France (Valensi 1996), Combe-Grenal layers 1–35 and 36–54 (45,000–71,000 years
ago and 71,000–115,000 years ago) are
from Domme in southwestern France
(Chase 1986; Delpech 1996; Mellars 1996),
and Gabasa (about 46,000 years ago) is
from Aragón near the Spanish Central Pyrenees (Blasco 1997). Preservation in the assemblages is comparable, and all are from
modern archaeological excavations. I compare these samples with 4 Upper Paleolithic
samples spanning 11,000–21,000 years ago
that were accumulated by fully modern humans from northern Spain: El Castillo
(Klein and Cruz-Uribe 1994; data provided
by R. Klein), El Juyo (Freeman et al. 1988;
data provided by R. Klein), Urtiaga (Altuna
1972), and La Riera (Straus and Clark
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JOURNAL OF MAMMALOGY
FIG. 4.—Mortality profiles of red deer (Cervus
elaphus) from Middle and Upper Paleolithic
sites in southwestern Europe. Histograms are
complete age profiles, and box plots compare
only adults. Methods for histogram and box-plot
construction are the same as in Fig. 2. Box plots
compare median m1 crown heights that were
standardized by average unworn crown height
for the sample to control for differences in body
size of red deer (Steele 2002). Mortality profiles
from Middle Paleolithic assemblages overlap
with assemblages from Upper Paleolithic sites.
Similar to modern humans, many Neanderthals
harvested many prime-age red deer. Data from
Steele (2002).
1986). Both samples from Combe-Grenal
and the Lazaret sample show hunting of
adult animals, whereas Gabasa has a high
proportion of young. When only adults are
considered in box plots, Gabasa’s median is
not significantly different from Upper Paleolithic samples, and the Combe-Grenal
and Lazaret samples fall within the range
of prime-age animals. These profiles sug-
Vol. 84, No. 2
gest that some groups of Middle Paleolithic
hunters regularly took prime red deer,
whereas other groups took mostly young
adults.
Other Middle Paleolithic sites show
strong evidence that Neanderthals had the
ability to regularly capture adult prey. Multiple sites ranging from 35,000 to 190,000
years ago in southern France, including La
Borde, Mauran, and Coudoulous, contain
large numbers (87–100%) of either steppe
bison (Bison priscus) or auroch (Bos primigenius—Jaubert and Brugal 1990). Similar sites also are located in Germany and
Russia (Gaudzinski 1996). Assemblages
from each of these sites produced mortality
profiles with high proportions of prime
adult individuals (Brugal and David 1993;
Slott-Moller 1990). The sites are all either
open-air or in sink-hole–type features. Archaeological and ethnographic evidence of
comparable species in North America suggests that these animals could have been
driven, and either sink holes (Jaubert and
Brugal 1990) or constructed barriers could
have been used to trap animals. The site of
Salzgitter Lebenstedt (54,000–58,000 years
ago) in northern Germany also is dominated
by adults of 1 species, reindeer (Rangifer
tarandus—Gaudzinski and Roebroeks
2000). The authors concluded that the site
indicates group kills, but the mortality profile shows an abundance of older adults; the
actual mode of accumulation remains unclear.
Examination of mortality profiles from
several sites reveals that the ability to regularly hunt adults of some prey species
emerged during the Middle Paleolithic of
Europe and Middle Stone Age of Africa.
This behavior apparently evolved in humans before other aspects of modern behavior appeared and before modern skeletal
anatomy became globally distributed approximately 50,000 years ago (Klein 1999,
2000a). Exact modes of prey acquisition remain obscure, and it is unclear if these early
hunters were taking individual prey in proportion to their abundance on the landscape,
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SPECIAL FEATURE—MAMMALIAN PALEONTOLOGY
driving entire herds (both would produce
mortality profiles closer to the idealized catastrophic structure), or targeting prime-age
individuals.
FUTURE RESEARCH
To understand the timing of changes in
human hunting strategies, more comprehensive comparative analyses must be undertaken. Although only a few examples are
presented here, mortality profiles during the
Late Pleistocene show great variation. Future analyses should include data from nonhuman carnivores, so that more paleontological comparisons can be made between
species. This also may allow the contexts
of predation decisions to be investigated.
As controls for archaeological studies, more
paleontological accumulations are needed
to understand better the pre- and postdepositional processes that affect skeletal remains from the time of death until excavation and to isolate the human component
of archaeological assemblages better. The
context of a fossil assemblage must always
be considered, and results should be regarded with caution until a consistent pattern
appears. Only in this comparative framework can behavior be reliably inferred from
fossil assemblages.
Mortality profiles of prey vary with the
predator species, and therefore they provide a powerful tool for illuminating how
predators select from prey populations. It is
possible to use mortality profiles to track
changes in predator behavior in the fossil
record, including the evolution of various
carnivore niches. In this study, I used mortality profiles to track human behavioral
evolution and showed that the human ability to consistently harvest prime-age animals developed before the origins of fully
modern humans. This conclusion is significant because it shows that starting well
back into the Pleistocene, humans hunted
differently from nonhuman predators, a
conclusion made possible by the study of
age distributions reconstructed from fossil
assemblages.
427
ACKNOWLEDGMENTS
I thank E. Hadly for inviting me to participate
in this symposium. I. Aguilera and V. Baldellou
(Huesca Musuem, Huesca, Spain), P. Utrilla and
F. Blasco (Universidad de Zaragoza, Zaragoza,
Spain), J. Altuna and K. Mariezkurrena (Sociedad de Ciencias Aranzadi, San Sebastián/Donostia, Spain), E. Tessier (Museo Arqueológico
de Asturias, Oviedo, Spain), H. de Lumley, A.
Echassoux, and P. Valensi (Laboratoire de Préhistoire du Lazaret, Nice, France), F. Delpech
(Université Bordeaux I, Talence, France), K.
Hamlin (Montana Department of Fish, Wildlife,
and Parks, Bozeman), L. Irby (Montana State
University, Bozeman), and J. Varley and D.
Smith (Center for Resources, Yellowstone National Park, Wyoming) generously provided access to faunal material. I thank E. Hadly, R.
Klein, T. Weaver, and 2 anonymous reviewers
for their comments on an earlier draft and J.
Rick for previous comments; R. Klein provided
some data and the animal and tooth drawings.
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