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Dental development of known-age chimpanzees Pan troglodytes (primates pongidae).

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AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY 86229-241 (19911
Dental Development of Known-Age Chimpanzees, Pan
troglodytes (Primates, Pongidae)
ROBERT L. ANEMONE, ELIZABETH S. WATTS, AND
DARIS R. SWINDLER
Department of Anthropology, State University of New York, Geneseo, New
York 14454 (R.L.A.);Department of Anthropology, Tulane University,
New Orleans, Louisiana 70118 (E.S.WJ; Department of Anthropology,
University of Washington, Seattle, Washington 98195 (D.R.S.)
KEY WORDS
Dental standards, Mandibular dentition, Growth
and development
ABSTRACT
Interpretation of dental development of fossil hominids requires understanding of and comparison with the pattern and timing of dental
development among living humans and pongids. We report the first study of
crown and root calcification in the lower permanent molar teeth among
chimpanzees (Pan troglodytes) of known chronological age. A series of 99
lateral head radiographs of 16 captive-born chimpanzees were analyzed.
Radiographs were taken at irregular intervals throughout the entire postnatal
period of dental development from birth to 13 years of age. Permanent
mandibular molars were rated on a n eight-point maturation scale from initial
radiographic appearance through crown and root calcification and apical
closure of the root canals. In addition, we were able to document initial crown
calcification and completion, as well as root completion and apical closure in
incisors, canines, and premolars. Our results show several differences from the
widely cited developmental schedule for pongid dentitions of Dean and Wood
(Folia Primatol. 361111-127, 1981). We found a much greater degree of
temporal overlap in calcification of the crowns of adjacent molars, a pattern
very unlike that usually seen in human dental development, which is characterized by delays between the onset of crown calcification in the molar series.
Also, the ages and durations of crown and root formation in our chimp sample
differ from the estimates proposed by Dean and Wood. By more clearly
establishing the nature of developmental schedules and the timing of major
events in the pongid dentition, these results should aid in the ongoing
controversies concerning the human or pongid nature of dental development
among Plio-Pleistocene hominids.
During the past few years there has been a
resurgence of interest among physical anthropologists in understanding the pattern
and timing of dental development among
Plio-Pleistocene hominid fossils (Lewin,
1987; Dean, 1987a, Beynon and Dean, 1988).
Attention has been focused on ascertaining
whether early hominids resembled modern
great apes or humans in their characteristic
schedules of dental development, including
tooth calcification and eruption sequences
(Dean, 1985; Smith, 1986,1987;Grine, 1987;
Conroy and Vannier, 1987, 1988; Mann et
al., 1987; Mann, 1988; Wolpoff et al., 1988).
@
1991 WILEY-LISS,INC
Independent approaches utilizing the presence of incremental growth markings in dental enamel have been used to ascertain the
timing of events in the dental development of
fossil hominids (Bromage and Dean, 1985;
Bromage, 1985, 1987; Dean et al., 1986;
Beynon and Wood, 1986,1987; Dean, 1987b;
Beynon and Dean, 1987). The point of departure for much of this research is Mann’s
Received March 5,1990; accepted November 21,1990.
Address reprint requests to Robert L. Anemone. Department of
Anthropology, Tulane University, New Orleans, LA 701 18.
230
R.L. ANEMONE ET AL.
(1975) monograph on the dental remains of
the Plio-Pleistocene hominids of southern
Africa. Relying heavily on the sample of
immature dentitions of Paranthropus robustus from Swartkrans, Mann (1975) argued
that the shared patterns of delayed development and eruption of the permanent molar
sequence between both robust and gracile
australopithecines and modern humans
strongly suggest a prolonged period of childhood dependency among these fossil taxa.
Elsewhere, Mann (1972:382) defined human
culture as a “set of learned behaviors that
modify the environment and are crucial to
the survival of the species.” Reasoning that a
long period of childhood dependency is best
explained as a n adaptation for learning the
skills involved in tool manufacture and usage, Mann(1975:84)stated that the evidence
of prolonged dental development among australopithecines is “the first direct morphological data for the presence of culture in this
hominid group.”
Mann’s (1975) opinion that fossil hominids
shared basically human schedules of growth
and development has only very recently been
reexamined by a series of workers (Bromage,
1985, 1987; Smith, 1986, 1987; Conroy and
Vannier, 1987,1988). Bromage (1987) questions the argument that the presence of prolonged dental development necessarily indicates a culture-bearing existence. A more
serious problem is Mann’s (1975) apparent
conclusion that the presence of a human
pattern of dental development among australopithecines implies human timing of developmental events (e.g., eruption of M1 a t 6
years, rather than a t 3.5 years, a s in apes),
and Smith’s (1986)counterargument that a n
apelike pattern implies a pongid rate of development. We see no valid basis for inferring rate from pattern, recognizing that
these two aspects of development may be
independent of each other.
An underlying theme in much of the discussion of dental development among fossil
hominids is the question of standards of
dental development for living humans and
great apes (Smith, 1986, 1987; Mann et al.,
1987; Lewin, 1987).While standards for both
the pattern and the timing of dental development among modern humans have been well
established in a number of longitudinal studies (Schour and Massler, 1940; Gleiser and
Hunt, 1955; Fanning, 1961; Moorrees, 1959;
Moorrees e t al., 1963; Demirjiran, 1986),the
same is not true for nonhuman primates
(Swindler, 1985). Longitudinal studies of
dental development involving animals of
known chronological age have been published for very few primate taxa, notably
Macaca mulatta (Hurme and Van Wagenen,
1961; Swindler and Gavan, 1962), Cebus
albifrons (Fleagle and Schaffler, 19821, and
Macaca nemestrina (Sirianni and Swindler,
1985). Published longitudinal studies of the
development of the pongid dentition are restricted to the emergence of the deciduous
(Nissen and Riesen, 1945) and permanent
(Nissen and Riesen, 1964) dentition of the
chimpanzee. The pongid standards for tooth
development cited in much of the recent
literature (e.g., Smith, 1986,1987;Bromage,
1987)are from a single cross-sectional radiographic study of museum specimens of unknown chronological age (Dean and Wood,
1981). Recently we have had the opportunity
to study a longitudinal series of lateral head
radiographs of chimpanzees (Pan troglodytes) of known chronological age. In this
paper we present findings on the development of the mandibular dentition in a n attempt to improve the published standards
for pongids.
MATERIALS AND METHODS
The subjects used in this study were 16
(eight male and eight female) chimpanzees
born and reared at the Yerkes Laboratories
of Primate Biology. Fifteen of these animals
were raised specifically for a longitudinal
study of growth and development (Nissen,
1942). Their growth (Gavan, 1953, 19711,
skeletal maturation (Nissen and Riesen,
1949a), and dental emergence (Nissen and
Riesen, 1945, 1964) have been reported in
previous publications. Information on the
parentage and treatment of the animals, as
well as the radiographic procedures, may be
found in these papers (see especially Nissen
and Riesen, 1949a). In addition to the 15
animals known as the Normative Group, we
have included data on one female, animal
120, who was used in a n experimental study
of the effects of light deprivation. Her skeletal development was found to be delayed
(Nissen and Riesen, 1949b). We include a
single X-ray of this animal, taken a t 48
months, in our sample because her dental
development appears to have been unaffected. Comparing her molar calcification
stages to those of the only other chimp with a
radiograph a t that age (male 61), she shows
identical stages in M1 and M2 and is actually
advanced in initial calcification of the M3
crown.
231
DENTAL DEVELOPMENT IN CHIMPANZEES
Although the lateral head radiographs
were collected a s part of the longitudinal
study, they are analyzed mainly in crosssectional fashion here due to certain inherent limitations of the data. While radiographs were taken for most animals every 2
to 3 months during the first few years of life
and yearly after about 4 years of age, lateral
head radiographs were not taken for each
animal at each examination. This resulted
in, for our purposes, many missing data
points (see Table 1and Fig. 1).The frequency
and length of these gaps make it difficult to
track longitudinally the development of individual teeth in individual animals from initial calcification to crown and root completion. In those individuals for whom sampling
is relatively complete, however, the longitudinal nature of the data allows estimation of
the rate a t which certain events in the dental
development of individual chimpanzees typically occur. For example, we can sometimes
determine the crown or root calcification
times for various teeth in individuals, a s well
a s the amount of time individual animals
remain in a given dental stage for various
teeth a t various different stages. Where possible, these kinds of inferences are drawn in
our analyses.
The eight dental stages used to describe
the development of chimp molar teeth were
modified versions of those defined by Demirjiran (1986) and Demirjiran et al. (1973) for
human molar development. They are illustrated in Figure 2 and described in Table 2.
The first four stages describe the development of the crown of the tooth from initial
calcification (A) through complete calcification to the level of the cementoenamel junction (D). The final four stages reflect increasing growth in length of the roots,
culminating in apical closure (H). We were
able to apply this model of dental development only to the permanent molar teeth
because anterior teeth were not easily observed on the lateral radiographs. Rather
than use the attainment of dental stages as a
basis for a dental maturity scoring system
(Demirjiran, 1986; Demirjiran et al., 19731,
we simply describe the calcification schedule
of the lower molar teeth in our chimpanzee
sample. We have also included, where the
data allow, observations on age a t initial
calcification as well as crown and root completion for the antemolar dentition. All radiographs were scored by one of us (R.L.A.),
while another of us (D.R.S.)examined nearly
all of the available radiographs and verified
the identifications. All radiographs of animals younger than 120 months were scored a
second time (by R.L.A.), a t the end of the
study, to verify the reliability of stage identification. There were very few differences in
the rescoring of radiographs, and none of
more than one dental stage. The age a t which
a dental stage was attained in a n individual
animal was recorded a s the age a t the first
radiographic appearance of that stage. This
procedure was used, rather than the standard procedure of using the mean age of the
TABLE 1 . Lateral head radiographs for individuals of Pan troglodytes
Individual'
M/55
M/57
MI59
M/61
M/65
M/67
M/71
M/79
F/90
F/94
F/98
FA00
F/102
FA04
F/ 106
F/120
Total
Aee2
120/156
120/132/144/156
84/96/108/120/132
8/24/36/48/108/120/132/144/156
15/18/27/42/96/120
10/12/96/108/120/132/144
1 day/2/4/7/84/96/108/120/132
1 day/72/84/96/120
24/36/108/120/132/144/156
3 weeks/21/108/120/132/144/156
12/108/120/132/144
12/18/96/108/120/132/144
15/33/96/108/120/132
1 day/2/4/6/8/12/72/84/96/108/120/132
1 day/2/10/18/21/24/96
48
Number
2
4
5
9
5
7
6
12
7
1
99
'M designates a male;F designates a female. The numbers are the animal identification numbers from the Yerkes
Primate Laboratories.
21n months, except where noted.
232
R.L.ANEMONE ET AL.
*
Number
of
Radiographs
O
10
m
-
0
Fig. 1. Histogram depicting the sample of lateral head radiographs of chimpanzees (Pan
troglodytes 1 on which this study is based. A total of 99 radiographs were examined. All ages are
in postnatal months except 1D = 1 day and 3W = 3 weeks.
roots of M1 can be said to begin development
a t approximately 24 months. All radiographs of individuals 72 months of age
(n = 1) and older (84 months, n = 2; 96
months, n = 5; 108 months, n = 4)show the
terminal stage of first molar development
(stage H) in which the cessation of root
growth is marked by apical closure. These
data might suggest that M1 roots take between 4 and 7 years to grow, but a closer
RESULTS
examination indicates otherwise. The atLower permanent molars
tainment of stage G in two animals a t 48
Figures 3-5 depict the calcification sched- months (F/120 and W61) suggests that apiule for the permanent lower molar teeth in cal closure takes place closer to 60 months.
our sample of Pan troglodytes. Initial calcifi- I n both M2 and M3, stage G is almost always
cation (stage A) of the crown of M1 was followed in the next year by the attainment
observed radiographically in all one day old of stage H. If this is also true for M1, we can
(n = 3) and three week old ( n = 1)chimpan- estimate a period of 3 years growth for the
zees (Fig. 3). The crown of M1 is completely roots of M1 in these animals. Due to the lack
calcified (stage D) by about the end of the of radiographs available for animals 60
second year of life. None of the animals months of age (Fig. 1 ), this suggestion must
observed had a complete M1 crown a t 18 remain speculative.
months ( n = 3, see Fig. 6), while all animals
Calcification of the second molar was first
older than 18 months had M1 in at least observed in one of two animals a t 15 months
stage D, including two animals at 21 months, of age (Fig. 4).By 18 months of age, two other
two at 24 months, and one a t 27 months. All individuals show initial calcification of M2
animals older than 27 months a s well as one (Fig. 6). By 21-27 months of age, all individindividual at 21 months (Fig. 7 ) had, in uals observed ( n = 5) have M2 in stage B
addition to a complete M1 crown, significant (Fig. 7). Eighteen months then appears to be
M1 root formation (Le., stages E-H). Since a good estimate for the onset of radiographiroot formation of molar teeth begins as calci- cally visible calcification of M2. Crown comfication of the crown reaches completion, the pletion first occurs at 48 months (n = 2) and
first radiographic appearance of a stage and
the last previous radiograph for t h a t individual (Swindler and Gavan, 1962; Fleagle and
Schaffler, 1982; Sirianni and Swindler,
1985),due to the sometimes significant gaps
between radiographs for individual animals.
Consequently, our results for the age at attainment of various dental stages must be
considered a s maximum values.
-
DENTAL DEVELOPMENT IN CHIMPANZEES
233
TABLE 2. Description of dental deuelopmental stages
of molar teeth in Pan troglodytes
Stages
A
11
c
Stane
DescnDtion
Initial cusp calcification is visible as one or a
series of small inverted cones in the upper
part of the crypt; there is no fusion of these
points
Initial points of calcification are fused, forming
a regularly outlined occlusal surface
Enamel formation is completed at the occlusal
surface with extension towards the cervical
region; dentine deposition has begun below
the enamel crown, and the pulp chamber has
a smoothly curved superior border
Crown is completely calcified to the
cementoenamel junction, and the beginnings
of root formation are present in the form of a
spicule
Radicular bifurcation is visible, while root
length is always less than crown height
Radicular bifurcation is further developed,
giving the roots a funnel shape; root length is
equal to or greater than crown height
Root canals are parallel sided with open apices
Completion of root length marked by apical
closure
D
E
F
G
H
Fig. 2. Develo mental stages used for molar teeth of
Pun troglodytes.&e Table 2 for description of criteria for
these stages.
is not evident at 42 (n = 1)and 36 months
(n = 2) of age. Two and one-half years is thus
a reasonable minimum estimate for the duration of calcification of the crown of M2. The
roots of M2 complete their growth (stage H)
at an age of 96 months (two of nine, 108
months (six of nine), or 120 months (six of
six). Second molar root formation can be
conservatively estimated as ranging between 3 and 6 years, with a more likely range
of 4-5 years.
The early developmental stages of M3 are,
unfortunately, poorly represented in this
data set (Fig. 5). The earliest calcification of
M3 appears in 1 individual at 42 months
(Fig. 8) and in one of two a t 48 months. The
fact that M3 is present in stage B or C in two
individuals at 72 months indicates that it
would almost certainly be present in these
individuals by at least 60 months. The best
suggestion that can be made from these data
is that M3 is first calcified at close to 48
months of age. Completion of the crown of
M3 occurs in two of three radiographs at 84
months and in all seven radiographs taken
at 96 months. A maximum estimate of 4.5
years for crown completion times of M3 can
be derived from one animal who was in stage
A a t 42 months and in stage D at 96 months
(W65). This value is a maximum (for this
individual), because no radiographs are
available between the ages of 42 and 96
lndividu
F190
Fl94
F198
F11 0 0
F l l 02
FllO4
FI106
F1120
MI55
MI57
MI59
Mi61
MI65
MI67
MI71
MI79
1D 3 W
2
4
7
6
8
10
12
15
18
21
24
27
33
36
F
D
A
42
48
72
84
E
B
c
B
C
A
A
A
?
B
B
B
E
B
9 6 108
H
H
H
H
H
H
B
C
D
D
H
G
H
D
B
B
B
A
A
E
C
G
D
H
H
F
H
E
B
A
H
Y
Fig. 3. Attainment of dental stages for M, o f P a n troglodytes. The letters A-H represent the
eight dental stages used in this study (illustrated in Fig. 2 and described in Table 2),and ?
indicates that the area in which the tooth is normally found was not present on the radiograph.
lndividua
F/90
Fi94
Fig8
F11 0 0
F11 0 2
F l l 04
Fl106
FI120
MI55
MI57
MI59
M/61
MI65
MI67
MI71
MI79
12
15
18
21
24
27
33
36
c
B
42
48
72
84
E
F
B
X
A
X
C
X
A
B
B
96 108120
G
H
H
H
G
G
H
G
H
G
H
G
D
H
H
B
A
B
A
F
G
G
F
H
G
H
G
H
G
D
C
C
X
E
H
H
H
Fig. 4. Attainment of dental stages for M, o f P a n troglodytes. The letters A-H represent the
eight dental stages used in this study (illustrated in Fig. 2 and described in Table 2);? indicates
that the area in which the tooth is normally found was not present on the radiograph, and x
indicates the absence of any calcification for the tooth.
Individual 1 8
F190
F194
Fl98
FIIOO
X
FllO2
Fl104
FllO6
F/120
MI55
MI57
MI59
MI61
MI65
MI67
MI71
MI79
21
24
27
33
36
42
48
72
84
C
D
X
X
X
X
9 6 108 1 2 0 1 3 2 1 4 4 1 5 6
E
E
F
G
H
F
G
G
H
E
F
H
D
D
E
F
G
D
E
F
G
D
E
F
G
D
A
C
D
X
X
A
B
E
C
D
D
E
D
E
E
E
F
G
F
E
F
F
F
G
F
H
G
?
F
G
H
H
H
G
H
H
Fig. 5. Attainment of dental stages for M, ofPan troglodytes. The letters A-H represent the
eight dental stages used in this study (illustrated in Figure 2 and described in Table 21; ?
indicates that the area in which the tooth is normally found was not present on the radiograph,
and x indicates the absence of any calcification for the tooth.
DENTAL DEVELOPMENT IN CHIMPANZEES
Fig. 6 . M/65 a t 18 months. Note that M1 is in stage C while M2 is in late stage A, with molar
cusps well developed but not quite fused to form a completely outlined occlusal surface. All
permanent teeth except M3 can be seen in their crypts in this radiograph. The entire deciduous
dentition is in occlusion.
Fig. 7. F/94 at 21 months. Note the beginnings of radicular bifurcation in M1, indicating the
attainment of stage E. M2 is in stage B, and all the other permanent teeth except M3 are clearly
present in their crypts.
235
236
R.L. ANEMONE ET AL
Fig. 8. M/65 at 42 months. M1 is in occlusion in stage F, M2 is in stage C, and M3 is in stage
A.
months. Another animal (IW79) had M3 in already present in stage A in four of five
stages B, C, and D a t ages 72, 84, and 96 radiographs (Fig. 6). Similarly, M3 is present
months, respectively. Assuming 1 year for in stage A in one individual a t 42 months
the transition from stage A to stage B indi- while M2 is still in stage C (Fig. 8).
cates 3 years of crown growth. The available
Lower permanent antemolar dentition
data do not rule out M3 crown completion
times anywhere in the range of 3-4.5 years.
Calcification of both permanent lower preThird molar root completion occurs at 132 molar teeth begins at 18 months in our sammonths (one of nine animals), 144 months ple of chimpanzees. Except for two radio(four of seven), or 156 months (four of four). graphs of poor quality in which the premolar
Simply looking a t the range in starting age region cannot be seen (FA06 a t 18 and 21
(84-108 months) and age at completion months of age), all animals of 18 months
(132-156 months) of the root gives a n over- (n = 21, 21 months (n = 11, and 24 months
estimate of the actual time involved. Looking (n = 3) of age show initial calcification of
a t these radiographs in a longitudinal fash- both P3 and P4. Time of crown completion of
ion, it is clear that most individuals remain the premolars is difficult to determine due to
in a single stage between D and H for a t most gaps in our data. One animal at 42 months
2 years, and usually for 1 year. This allows us ( W 6 5 ) has crowns of P3 and P4 one-half to
to estimate minimum and maximum values three-quarters complete, while another at 72
months (W79) has complete crowns of
for M3 root growth of 4-5 years.
These results indicate a substantial unerupted P3 and P4 as well as some initial
amount of overlap in the crown development root formation on P3. These few data suggest
of adjacent molars among chimps. In our crown completion of P3 and P4 between 5
sample of chimpanzees, M1 is radiographi- and 6 years of age. Apical closure of the
cally present a t birth and reaches crown premolar roots occurs in all individuals
completion a t 2 years of age o r slightly ear- (n = 14) a t either 9 or 10 years of age.
Permanent lower incisor teeth first aplier. By 15-18 months of age, however, when
M1 is in either stage B or stage C, M2 is pear radiographically in one individual (F/
DENTAL DEVELOPMENT IN CHIMPANZEES
104)at 6 months (11)and 8 months (12).Both
permanent incisors are, however, absent in
two other animals aged 7 months (W71) and
8 months (W61). All animals 10 months of
age and older have both permanent lower
incisors present. Incisal crown completion is
attained by about 3 years of age, as seen in
animals with crowns of both I1 and I2 complete a t 33 months (F/102),36 months (F/90),
and 42 months (W65). The condition of the
permanent lower incisors in another 36month-old animal W 6 1 ) is, unfortunately,
impossible to determine. Apical closure of
the incisor roots has apparently occurred by
about 7 years of age ( n = 4).
The permanent canine is visible in one
(F/104) of four animals a t 12 months and in
one (W65) of two a t 15 months of age. By 18
months of age and older, the permanent
canine is always present in our sample. The
canine crown is completely calcified by about
7 years of age ( n = 4) or slightly older. The
canine root reaches apical closure at about
12 years of age ( n = 7).
DISCUSSION
The question of which standards of human
dental development should be used in attempting to describe the patterns and rates
of dental development among fossil hominids has recently been the subject of serious
debate (Smith, 1986, 1987; Mann et al.,
1987; Lewin, 1987). It is therefore surprising, considering the many fewer available
data, that there has been little discussion of
the suitability of the standards used to describe dental development among pongids.
While there is a tendency to view the dentitions of fossil hominids in a dichotomous
fashion’as sharing either a “human” or a
“pongid” pattern of dental development
(Mann, 1975), most recent investigators
(e.g., Smith, 1986; Conroy and Vannier,
1987; Beynon and Dean, 1987,1988; Beynon
and Wood, 1987) are considering more seriously the possibility that some or all of the
fossils have had unique patterns and/or
rates of dental development. In any event,
longitudinal data on animals of known age
are needed to characterize pongid dental
development accurately, and until now these
have been lacking. The data presented here
allow a clear characterization of the developmental pattern and rate of the chimpanzee
dentition.
The most commonly cited reference on
pongid dental development is the pioneering
contribution of Dean and Wood (1981).These
237
authors made a radiographic analysis of a
cross-sectional museum sample of the skulls
and jaws of 175juvenile wild-shot apes (Pan
troglodytes, Pongo pygmaeus, and Gorilla
gorilla). This paper was the first reasonably
successful attempt at developing standards
of dental development among apes for comparison with the well known human standards. The developing ape teeth were scored
on a nine-point maturation scale very similar to the eight-point scale used in this study.
Using published data on gingival emergence
of the chimpanzee dentition (Nissen and Riesen, 1945, 1964), a series of extrapolations
were made to estimate the age a t which
dental development events occur among
pongids. Since these animals were obviously
of unknown age a t death, Dean and Wood
(1981) made the following assumptions: 1)
crown calcification time for all molars is 2.5
years and 2) roots of similar tooth types
calcify in the same period of time.
Dean and Wood (1981:113) clearly understood the limitations inherent in their use of
cross-sectional data, and stated that “without longitudinal data i t is impossible to establish the variability of dental development
with chronological age; only the relative dental developmental age of a n ape skull can be
established from cross-sectional data such as
these.” In any event, their work, and especially their Figure 2 (Dean and Wood,
1981:116; adapted as part of our Fig. 9), has
been cited as a n important reference on dental development among the pongids and the
crux of the comparison of fossil hominid dentitions with those of modern pongids (Smith,
1986,1987; Bromage, 1987; Dean, 1987a, b).
The results reported here, a s well a s our
reading of the literature, indicate that both
of the above assumptions may be invalid and
that the time scale of pongid dental development needs recalibration.
In support of their assumption that all
three molars calcify in approximately the
same amount of time among pongids, Dean
and Wood (1981) cite two longitudinal studies ofhuman dentition. In the first, Moorrees
et al. (1963) estimate the time for crown
calcification of the human M1 a s 2.1 years
and for M2 and M3 a s 2.8 years. In the
second, Gleiser and Hunt (1955)present no
data on crown calcification times for M2 and
M3. Their article concerns the first molar, for
which they estimate crown completion times
of 41.5 months sd = 5.6) for boys and 39.3
months (sd = 4.2/months) for girls, and
which they describe as “the tooth which un-
238
R.L. ANEMONE ET AL
Human
I I I I I I I I I I I I I I I I I I I ]Years
1 2
3
4
6
5
7
9 10 11 12 13 14 15 16 17 18 19 20
8
Pongid
I1
I2
B.
C
P,
p4
M,
M
M
I
c-
I:
C
P
P
M
M
M
I I I I I I I I I I I I I I I I I I I /Years
1 2
3
4
5
6
7
8
9 10 11 12 13 14 15 16 17 18 19 20
Fig. 9. Crown and root calcification and gingival emergence schedule for human ( A ) )and
pongid (B)samples (After Dean and Wood, 19811,and forPun troglodytes (C).Plottedvalues are
means or estimated means. Solid lines show crown formation; dashed lines show root formation;
E, gingival emergence. Emergence data in both B and C are from Nissen and Riesen, (1964).
DENTAL DEVELOPMENT IN CHIMPANZEES
dergoes the fastest amelogenesis . . . in the
permanent dentition” (Gleiser and Hunt,
1955:270).Both Fleagle and Schaffler (1982)
and Sirianni and Swindler (1985) found a
progressive lengthening of the period of
crown calcification from the first to the third
permanent molar in their longitudinal studies of Cebus albifrons and Macaca nemestrina, respectively. In examining our data, we
find no support for the assumption of equal
periods of calcification for each of the permanent molars in Pan troglodytes. Our best
estimates for molar crown calcification times
are 2 years for M1,2.5 years for M2, and 3.5
years for M3.
Lacking sufficient temporal information
on root development, Dean and Wood (1981)
made the assumption that the roots of similar tooth types (e.g., all molars, all premolars) develop in the same period of time.
Moorrees et al. (1963) indicate that the situation is somewhat more complex among humans, where M1 root calcification time is
estimated a s 3.6 years, M2 as 4.8 years, and
M3 a s 4.5 years. The data on human premolar root calcification times indicate little difference between P3 and P4, but a significant
sexual difference, with males ranging from
5.3 to 5.4 years and females from 4.6 to 4.9
years (Moorrees et al., 1963). Fleagle and
Schaffler’s (1982) data on C. albifrons similarly show differences in P3 and P4 root
development times of males (P3 106.03
weeks, P4 105.95 weeks) and females (P3
93.86 weeks, P4 96.32 weeks) but no intrasexual differences between the P3 and P4.
Their data also indicate a lengthening period
of root calcification from the first to the third
molar in both male and female C. albifrons
(Fleagle and Schaffler, 1982).Likewise, Sirianni and Swindler’s (1985)study ofM. nemestrina also documents a n increase in root
calcification time from the first to the third
molar in both males and females, but no
significant differences in the root calcification times of P3 and P4. Similarly, the data
presented here suggest variation in the root
calcification times of the molar teeth, but not
the premolars, among Pan troglodytes. We
estimate that the root of M1 develops for a
period of 3-4 years, M2 and M3 roots develop
for approximately 4-5 years, and the roots of
both P3 and P4 calcify in 4-5 years.
In spite of the problems with these two
assumptions (crown calcification times of 2.5
years for all molars and equal period of root
development for similar tooth types), they
form the basis for much of Dean and Wood’s
239
(1981) proposed schedule of dental development among pongids. Our data suggest a
substantially different schedule of dental development for P. troglodytes (Fig. 9).Perhaps
the most significant difference between our
results and those of Dean and Wood (1981)
can be seen in the period of crown calcification of the molar dentition and in the degree
of overlap in development of adjacent molars. Dean and Wood (1981) apparently
found no overlap between the developing
crowns of adjacent molars and indicated sequential 2.5 year periods of crown calcification for these teeth, beginning a t birth (Ml),
2.5 years of age (M21,and 5 years of age (M3).
Our results show a substantial amount of
overlap in the crown development of adjacent molars. This is a particularly interesting finding in that it accentuates the major
difference between human and pongid
schedules of molar development, that of delayed onset of calcification of the molar series in humans (Moorrees et al., 1963).Fanning and Moorrees (1969) suggest that
temporal overlap in calcification of second
and third mandibular molar crowns occurs
at low frequencies in some modern human
populations, including Europeans (4%) and
aboriginal Australians (14%). While suggestive, these data do not strongly contradict
the evidence for important differences between pongid and human schedules of molar
calcification. Our results serve to distinguish more easily between human and
pongid developmental schedules by indicating a greater degree of temporal overlap in
the calcification of the crowns of adjacent
molar teeth in chimpanzees than apparent
in earlier published studies (e.g., Dean and
Wood, 1981). These results are consistent
with, and to some extent explain, the progressive delay in eruption of the permanent
molar teeth among humans compared with
apes relative to chronological age, to eruption of the anterior teeth, and also to epiphyseal union noted by Schultz (1956). Differences between our estimates and those of
Dean and Wood (1981)in the period of molar
root formation appear to be of only minor
importance (Fig. 9).
While our results for the antemolar dentition are less compelling than those for the
molars, we were in most cases able to estimate the onset and completion of crown and,
to a lesser extent, root calcification. Premolar development in our sample begins somewhat earlier than estimated by Dean and
Wood (1981).We have clear evidence of ini-
240
R.L. ANEMONE ET AL
tial calcification of both P3 and P4 at 18
months, while Dean and Wood (1981) published ages of slightly greater than 2 years
for these events. Premolar crown completion
in both their estimate and ours occurs at
about 5 years of age for both P3 and P4.
Conversely, our data indicate a slightly later
onset of calcification of the incisors (6-10
months) than those of Dean and Wood (1981)
( 2 4 months). No major differences are apparent in the development of the canine
crown or root or in the development of the
roots of any other permanent mandibular
teeth.
In summary, our analysis of a mixed longitudinal series of lateral head radiographs of
chimpanzees of known chronological age has
allowed us t o modify published standards of
dental development for modern pongids.
Concerning the development of the lower
permanent molar teeth, for which our data
are most complete, our results indicate the
following: 1)The duration of crown calcification of adjacent molar teeth overlaps to a
considerable extent. This contrasts with the
usual human schedule of delayed onset of
crown calcification among adjacent molar
teeth. 2) The duration of crown and root
development appears to increase from the
first to the last molar tooth. 3)Ages at initial
calcification and completion of the crowns
and roots of the lower permanent molars, as
well as some of the antemolar teeth, differ
from the previously published estimates of
Dean and Wood (1981).
ACKNOWLEDGMENTS
Funding for collection of the original
growth data and radiographs, as well as
maintenance of the chimpanzees was provided by the Samuel s.Fels Fund and grant
RR00165 from the Yerkes Laboratories of
Primate Biology (Orange Park, Florida). We
thank the Yerkes Regional Primate Research Center of Emory University for use of
the X-rays on which this study is based. We
also thank Ron Pretzer and Ray Mayo of
Instructional Resources at SUNY Geneseo
for their help in preparing Figures 6-8 (R.P.)
and Figures 2 and 9 (R.M.).
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