Biomedical Engineering Reference
In-Depth Information
Skeletal maturation involves achievement of full adult limb
length prior to full adult body length. The actual timing of
the fusing of the various epiphyseal elements varies
between the sexes and among the species, but the basic
pattern of fusion remains fairly constant in all primates.
Dental maturation, particularly the full eruption of the last
(third) molar, usually occurs around the same time as
skeletal maturity. The final component of the adult body
physique to mature is body weight.
Middle (or prime) age adulthood, the longest of the
three phases of adulthood, is characterized by morpho-
logical stability with few, very gradual changes over the
years. The term adult in the literature generally refers to
this phase. Most of the changes which do occur during this
period are cyclic in nature and related to breeding/
seasonal fluctuations and are thus temporary in nature.
Pathological conditions related to aging, e.g. arthritis,
develop during this period, but they do not noticeably
affect the morphology or the behavior of the animal. Since
the rate of development of some pathological conditions is
influenced by environmental conditions, the actual chro-
nological age of animals in their prime may vary even
within a single species ( DeRousseau et al., 1986; Kessler
et al., 1986b ).
Aged adulthood is the last phase in the life cycle.
There are no specific criteria that separate prime from
aged animals but rather the cumulative effect of
numerous morphological changes over the years. Systems
typically affected by aging are the musculoskeletal,
ophthalmological, neurological, and immunological
systems. Most of the pathologies seen in nonhuman
primates are those common to all mammalian species,
including humans. In addition to pathological conditions
per se, aged adulthood is also characterized by a general
reductioninbodysize(i.e.wasting) and a decline in
breeding success.
The basic morphological characteristics distinguishing
the different life cycle phases are constant in primates, but
vary considerably between species, and even between sexes
of the same species, in their degree of expression. In
addition to genetic factors, social and environmental factors
contribute significantly to the morphology of nonhuman
primates. In species with structured social orders, the
morphology of an individual may be altered by rank due to
access to food or other less tangible factors. Environmental
conditions can also affect the morphology of individuals as
evidenced in comparisons between free-ranging and labo-
ratory animals ( Knezevich and DeRousseau, 1985; Kessler
et al., 1986b; Turnquist, 1983, 1984a, 1985; Turnquist and
Kessler, 1990b; Zihlman et al., 2007 ). This effect is not
necessarily only the result of nutritional differences, but
also the result of differences in physical space and types of
supports provided as well as social and psychological
factors.
Dental and Skeletal Maturation
The sequence and age of dental eruption are now available
for many primate species ( Smith et al., 1994; Swindler,
2002; Zihlman et al., 2007; Setchell and Wickings, 2004;
Henderson, 2007; Harvati, 2000 ). The data show varia-
tions in the sequence of eruption in some teeth. In general,
however, the first permanent teeth to erupt in higher
primates are the first molars and the last to erupt are either
the premolars and canines or the third molars. The
sequence of eruption of the second molars, the incisors,
the third molars, and the premolar
canine complex varies
among species. In most Old World monkeys and great and
lesser apes, the second molars erupt after the incisors and
the third molars after the premolars and canines. In mostly
foliverous Colobus, however, the second molars erupt
after the central incisors and before the lateral incisors, but
the premolar
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third molar sequence is the same as
in other Old World monkeys. In New World monkeys,
there is considerable variation in the sequence of second
and third molar eruption relative to the other teeth
( Cheverud, 1981; Fleagle, 1999; Schultz, 1933; Swindler,
1985, 2002; Turnquist and Kessler, 1990a,b ). There is
some evidence that dental eruption, like skeletal maturity,
may be affected by environmental conditions, including
captivity ( Phillips-Conroy and Jolly, 1988; Zihlman et al.,
2007 ).
The appearance and development of ossification
centers in the extremities and the fusion of epiphyseal
plates provide a means for evaluating the age of immature
animals ( Michejda, 1987 ).Duetothesmallsizeofthe
manual skeleton in many species of nonhuman primates,
Silverman et al. (1983) recommend the knee and ankle
complexes for evaluating skeletal maturation over the
hand-wrist region preferably used for humans. Each
species appears to have its own distinct timing for skeletal
development, but actual data are not available for many
species ( Watts, 1990b ). Watts (1986) summarized the
scant primate data available on the development of ossi-
fication centers both pre- and postnatally and discussed
the apparent major differences in timing and sequence.
The same article also summarized all the then available
data on the age and sequence of epiphyseal fusion in
primates. Since environmental conditions (e.g. laboratory
versus free-ranging) affect both of these factors, published
standards for even the most common primate (rhesus
macaques) should be used with caution. Cheverud's
(1981) evaluation of epiphyseal fusion in skeletal material
of known age, free-ranging rhesus macaques from Cayo
Santiago, and the evaluation by Silverman et al. (1983) of
skeletal maturation in rhesus macaques of known age born
and raised at the Oregon Regional Primate Research
Center (ORPRC) should be consulted when evaluating
skeletal development.
canine
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