Age DeterminationTwo approaches are
commonly used to determine an animal’s age at death. One
deals with long bone fusion while the other focuses on
dentition. Both have their pros and cons, and it is advised
that data from both be presented whenever possible (Crabtree
1990).
Long bone fusion rates published by Silver (1969) serve as
the standard reference for animal bone archaeologists.
Fusion rates of the epiphysis at the end of a bone, or
epiphyseal fusion, vary by bone, location of fusion area
(top or bottom of bone), and species. Epiphyseal fusion is a
widely used method among practicing zooarchaeologists, but
it is not without its problems. Fusion rates are relatively
imprecise and the affects of varying nutrition are poorly
understood (Davis 1987:39). Crabtree (1990:162) also notes
that in addition to nutrition, different breeds and
castration also influence fusion rates. Fusion data have
limited applicability in that they cannot assess the age of
an animal after the latest point of fusion. For example, the
latest fusion rates from sheep occur on the proximal humerus
at 3.5 years (Silver 1969:252); therefore, once all centers
have already fully fused, this method cannot be used to
calculate advanced ages.
Ovicaprine fusion rates are calculated by grouping those
bones that fuse at approximately the same stage in the
animal’s life. The number of fused bones is divided into the
sum of the fused and unfused bones for a particular age
class, and is then expressed as a percentage. This value
represents the frequency of ovicaprines surviving beyond a
particular age class. An example drawn from the raw scores
for the ovicaprine fusion data is illustrated in
Table 2.
For example, 22 bones are associated with centers that fuse
at around 10 months old. The value is then divided into the
total number of bones (34) for this particular age class.
The result shows that 64.7% of the ovicaprines survived
their first 6-10 months of life. The sum of the percentage
values does not equal 100 because each age class is treated
as a self-contained data set and is considered individually
from other age categories. Therefore, the percentage values
are specific to the age group in which they appear.
 A total of 122 proximal/distal bone ends were used to
compute ovicaprine mortality from the 8th century Moabite
Fortress at Mudaybic, presented in
Figure 7  . Each bar is
divided into an upper and lower register; the upper
represents the remains of those animals surviving beyond
that particular age class, while the lower value represents
the remains of animals killed within that age category. The
observed mortality profile is considered in light of
expected profiles that are product specific, that is,
whether animals were raised for meat or dairy products. Meat
producing economies with sheep normally kill young males
once they achieve optimal weight gain, after which time the
added bulk they accumulate is disproportionate to the amount
of fodder required. Slaughter, then, is an economic
consideration as it seeks to establish balance between the
greatest bulk of the animal and the amount of food needed to
achieve it. Animals are usually killed in their second or
third year of life, while only a few males surviving into
their later years are used for breeding (Payne 1973:281). As
seen in Figure 7 , the kill off rate for age classes
corresponding to animals in their second and third year
peaks, albeit only marginally, at 18-30 months. Many animals
are also culled from the herd from earlier (10 months) and
later (36-42 months). Significant kill off peaks at
different times could indicate interest in both meat and
dairy production, and perhaps some of the remains from older
animals represent a few milk producing females. Since the
body part distribution (below) indicates whole animals were
not regularly kept at the site, exploitation strategies
probably did not focus on large scale dairy production.
Dental attrition rates were defined by Payne (1973) and
Grant (1982). Codes for some of the main domesticated
animals, such as cattle, sheep, goats, and pigs, have been
determined to correspond to a specific age or stage. The
state of dental wear is assumed to reflect the age of the
animal; teeth from the oldest individuals will exhibit the
greatest amount of attrition, whereas those from younger
individuals exhibit less wear and are more often
characterized by cusps in pristine condition.
 Payne’s model (1973) can be used to score the teeth of sheep
and goats. His method specifically applies to mandibular
molars and premolars. The method also requires that
mandibular teeth be still set into the jaw rather than
recording wear stages for isolated lower teeth. The reason
is that scores for each tooth are considered as a series of
datum points. An animal’s age at death can be more
accurately estimated if the attrition scores from two or
more teeth can be recorded from the same jaw, converging on
a relatively small age range. Using isolated teeth results
in less accurate estimates for age at death, expressed as
greater age ranges, thereby inhibiting interpretation of the
data. In Figure
8
we see two halves of ovicaprine mandibles
from two different animals. Based on the wear on the chewing
surface of the teeth, which mandible is from the older
animal? Check for the answer at the end the article
following the works cited.
It should be noted that not all kinds of tooth wear are
directly linked to an animal’s age. Grant (1978:104) noted
abrasive foods can influence the rate and nature of wear, as
can soil types with more grit and greater acidity. Also, if
an animal experienced injury or an abscessed tooth, it may
prefer to chew on the unaffected side. By avoiding
irritation, this would artificially inflate the degree of
wear on the opposite overused side of the jaw. Premature
incisor loss will also affect an animal’s ability to graze,
thereby influencing tooth wear.
Dental eruption sequences are also used for determining age
and are species specific (Silver 1969). This method is
especially useful for recognizing ages for juveniles and
sub-adults. However, it should be noted that poor nutrition
can affect an animal’s tooth eruption. One of the
limitations of dental eruption sequences is that it cannot
be applied to species with rootless incisors (Hesse and
Wapnish 1985:76). Incisors without closed roots continue to
grow throughout the life of the animal, as enamel is
constantly accreted to the base of the crown (Davis
1987:42).
There are advantages to relying on dental information for
establishing an animal’s age at death, which have been
clearly outlined by Payne (1973:281, 1985:145) and Klein and
Cruz-Uribe (1984:43). Dental information can identify the
presence of the young and the very old in a herd, since
teeth continuously record the age of an individual
throughout the course of its life. Due to this biological
fact and that teeth are generally more durable and numerous
than long bones, they are an excellent source of aging data.
However, it is important to note that tooth wear tends to
under-represent very young individuals (less than 6 months
old); their teeth are not as durable and are more easily
destroyed (Wapnish and Hesse 1988:89).
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