close

Вход

Забыли?

вход по аккаунту

?

Dental development in South African australopithecines. Part II Dental stage assessment

код для вставкиСкачать
AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY 86:137-156 (1991)
Dental Development in South African Australopithecines.
Part II: Dental Stage Assessment
GLENN C. CONROY AND MICHAEL W. VANNIER
Department of Anatomy and Neurobiology and Department of
Anthropology fG.C.C.1Mallinckrodt Institute of Radiology (M.W.V.),
Washington University School of Medicine, St. Louis, Missouri 63110
KEY WORDS
Australopithecus, Computerized tomography, Human evolution, Dental maturation
ABSTRACT
Dental development stages of six immature Australopithecus
robustus individuals from Swarktrans (SK 61, SK 62, SK 63, SK 64, SK 438,
SK 3978) and seven immature Australopithecus africanus individuals from
Taung, Sterkfontein, and Makapans (Taung 1, Sts 2, Sts 8, Sts 18,Sts 24, Stw
327, MLD 2) are described. These stages were assessed using the system
devised by Demirjian and colleagues and were based on a data set comprising
over 350 computed tomographic (CT) scans taken a t 1 and 2 m m slice
intervals. It is concluded that patterns of dental development may have
differed between A . robustus and A. africanus even though the chronology of
development (i.e., the length of time for dental development to occur)may have
proceeded relatively rapidly in both species. These data provide unique
information regarding the timing and pattern of dental maturation in australopithecines and can be used to compare and contrast developmental patterns
among early hominids, modern humans, and nonhuman primates.
The concept of physiological age in living
subjects is based on the degree of maturation
of different body tissue systems. Over the
years, several biological ages have been developed to assess this: skeletal age, secondary sex character age, dental age, and so
forth (Moorrees et al., 1963; Smith, 1989).
Given that most fossil taxa are best known
from teeth and jaws, the aging system most
appropriate to paleontological study is, of
course, dental age. Fortunately, dental aging
patterns are quite robust in that many studies have shown that they are little, if at all,
affected by altered environmental conditions
(Nissen and Riesen, 1964; Demijian, 1986;
Smith, 1991). Until fairly recently, dental
eruption, or emergence as it is called here,
has been the main criterion used to assess
dental maturity in both living and fossil
subjects (Weidenreich, 1937; Broom and
Robinson, 1951; Garn et al., 1957; Garn and
Lewis, 1963; Wallace, 1977). However, dental emergence represents only one stage in
the continuous process of tooth migration to
the occlusal level. Within the past few decades researchers have recognized that as-
@ 1991 WILEY-LISS, INC
pects of tooth and root formation, rather
than tooth emergence alone, are more reliable indicators of dental maturity (e.g.,
Moorrees et al., 1963; Demijian et al., 1973;
Mann, 1975; Dean and Wood, 1981; Fleagle
and Schaffler, 1982; Smith, 1986; Beynon
and Dean, 1988; Simpson et a]., 1990).
Over the past few years, two issues concerning australopithecine dental development have become particularly controversial: 1) are dental development patterns
distinctive between A . robustus and A . africanus (Broom and Robinson, 1951; Mann,
1988; Mann et al., 1987; Dean, 1985; Grine,
1987; Conroy, 1988;Beynon and Dean, 1988)
and 2 ) are dental development chronologies
distinctive between australopithecines and
modern humans (Mann, 1975; Bromage and
Dean, 1985; Smith, 1986; Dean, 1987,1988;
Conroy and Vannier, 1987,1992;Simpson et
Received March 5,1990; accepted November 12,1990,
Address reprint requests to Dr. Glenn C. Conroy, Department
o f h a t o m y and Neurobiology, Box 8108,Washington University
School of Medicine, St. Louis, MO 63110.
138
G.C. CONROY AND M.W. VANNIER
al., 1990; Wolpoff et al., 1988).Thepattern of
dental development refers to the way (or
order) in which various teeth develop and
emerge in relation to one another, while the
chronology of dental development refers to
the absolute length of time required for dental maturation to take place (see Conroy and
Vannier, 1991; Dean, 1988). As is well
known, the chronology (absolute time) of
dental maturation in modern humans takes
about twice as long to complete as in modern
pongids. Even though dental development
patterns may be more humanlike in one
australopithecine species than in another,
this does not necessarily imply that such
development followed a humanlike chronology. In other words, chronology and pattern
are two separate issues in that a humanlike
pattern may still have developed during an
absolute growth period comparable to that of
extant pongids. At present, determination of
an absolute chronological age for any given
fossil specimen is only attainable by perikymata counts, and these indicate a rapid maturation rate for australopithecine teeth
(Dean, 1987; Beynon and Dean, 1988). Such
conclusions are, of course, only as reliable as
the assumptions they are based upon.
The purpose of this study is to provide
basic dental development data on a large
sample of immature South African australopithecines, including representatives of both
Australopithecus africanus and A. robustus
(Taung 1,Sts 2, Sts 8, Sts 18,Sts 24, Stw 327,
MLD 2, SK 61, SK 62, SK 63, SK 64, SK 438,
SK 3978).These data can be used to compare
and contrast dental maturation patterns
among australopithecines, modern humans,
and nonhuman primates.
MATERIALS AND METHODS
Our assessment of dental development in
South African australopithecines is both
qualitative and quantitative and is based on
the evaluation of over 350 computed tomographic (CT)scans taken at 1and 2 mm slice
thicknesses. All scans were taken on a Siemens DR3 CT scanner in the Radiology Department of the Hillbrow Hospital, Johannesburg, South Africa. The uncompressed
512 x 512 CT scans and digital radiographs
(topograms) were stored on 8 inch doublesided, double-density, floppy disks and
brought back to our laboratories at Washington University Medical School, where they
were analyzed on a Siemens Evaluscope-DR
reviewing console. Hard copies of all images
were made using a Matrix Instruments MI10 camera. Extended bone range window
settings were used since the heavily mineralized fossils were well beyond +1,000
Hounsfield units (with the x-ray tube operated a t 125 kvp), the upper limit of normal
CT viewing.
All measurements were made directly on
the CT images by using the x-y digitizer pad
and DISTANCE program built into the Evaluscope-DR reviewing console. A cautionary
note is in order concerning the measurements provided here. In CT scans the most
accurate measurements are those in which
the object of interest is in the precise plane of
section of the CT beam. When taking serial
CT slices through a complex three-dimensional structure like a mandible, individual
teeth are rarely oriented precisely in the
plane of the CT beam. For this reason, contiguous 1 and 2 mm thin CT sections were
taken through the entire specimen so that
details of root andlor crown formation could
be followed through successive slices. We
have recorded measurements only to the
nearest millimeter and only for those measures that would be difficult or impossible to
obtain otherwise without some destruction
of the original specimen (e.g., crown lengths
of unerupted teeth, root lengths, enamel
thicknesses, and so forth). Scales are provided with each CT scan so that others may
evaluate structures of interest to them that
may not be discussed here.
The imprecision of the absolute measurements does not affect the assessment of dental stages. These stages, as defined by
Demirjian et al. (19731, are based on a qualitative assessment of crown and root formation. Eight distinct stages are identified for
each developing permanent tooth (Fig. 1).
Observations are also recorded for many of
the deciduous teeth.
RESULTS
Australop ithecus robust us
SK 438 (Table 1;Fig. 2). SK 438 is part of
an immature mandible with emerging left
dp4 and unerupted M1. The followingresults
are based on a contiguous series of nine
parasagittal CT scans taken at 1mm intervals.
The absence of wear facets on dp4 indicates that it had not yet come into occlusion.
The emerging tooth is rotated so that its
occlusal surface faces in a posterosuperior
DENTAL STAGE ASSESSMENT
direction. Enamel thickness at the midpoint
of the tooth is estimated between 1 and
2mm. Crown height and root lengths are
approximately 5 4 mm.
There is no evidence of P4 calcification
(stage 0).
Enamel formation on the unerupted M1 is
complete a t the occlusal surface with extension and convergence toward the cervical
margin. There is no evidence of root formation. The developing tooth is oriented so that
its occlusal surface faces in an anterosuperior direction. The occlusal surfaces of the
dp4 and M1 form an angle of about 120"
between them. Crown length is estimated a t
12-13mm and crown height a t 6mm.
Enamel thickness is between 1and 2 mm a t
the midpoint of the tooth and about 2 mm
beneath the mesial cusps. This tooth is
scored between dental stages 3 and 4.
SK 64 (Table 1;Fig. 3a,b). SK 64 is part of
an immature mandible with right dp3, dp4,
and unerupted M1. The followingresults are
based on a contiguous series of 17 parasagittal CT scans taken at 1 mm intervals.
Based on the emergence status of dp4, this
individual is considered slightly older than
SK 438. The dp4 emerged fairly recently,
however, since there is little wear on its
occlusal surface. Note the thicker enamel on
dp4 compared with dp3: Enamel thickness is
slightly less than 1.0 mm on dp3 and slightly
greater than 1.0 mm on dp4. There is about
5 mm of root still preserved on dp3 and about
7 mm on dp4 (Fig. 3a).
P3 calcification had recently begun. Fusion of the calcified points of the cusps have
united to give an outline of the occlusal
surface (stage 2).
There is no trace of P4 calcification (stage
0).
M1 enamel formation is complete at the
occlusal surface with extension and convergence toward the cervical region. Dentinal
deposition is also evident, but root formation
had not yet commenced. M1 crown length is
estimated a t 12-13 mm. This tooth is scored
between dental stages 3 and 4.
It appears that M2 crypt formation may
have begun (Fig. 3b).
SK 3978 (Table 1; Fig. 4a-d). SK 3978 is
part of an immature mandible preserving
alveoli for left and right dil, di2, and dc,
crowns of left and right dp3 and dp4, and
unerupted left M1. The following results are
based on a contiguous series of 24 parasagittal CT scans taken at 1 mm intervals.
139
Portions of the deciduous canine and incisor roots are still preserved in their alveoli,
and estimates of their lengths can be given.
The alveoli of the left dc, left di2, and right
dil are at least 8,7, and 4 mm deep, respectively (Fig. 4a-c:).
Enamel thickness of the deciduous premolars is worn to less than 1mm in dp3 and to
about 1 mm in dp4. The length of the dp3 and
dp4 roots are approximately 6 and 9mm,
respectively (Fig. 4a).
Enamel formation of the permanent incisors and canines is complete at the occlusal
surface and extends toward the cervial region. The incomplete incisor and canine
crown heights are estimated at 6-7mm.
Dentinal deposition is clearly seen in these
teeth (Fig. 4b,c). Incisors and canines are
scored at dental stage 3.
Fusion of the calcified cusps on the P3
have united to give a regular outline to its
occlusal surface (stage 2) (Fig. 4a).
There is no evidence of P4 calcification as
yet.
M1 enamel formation is complete at the
occlusal surface and extends and converges
toward the cervical region. Root formation is
not evident. Crown length is about 13 mm.
This tooth is scored between dental stages 3
and 4 (Fig. 4d).
As in SK 64, there is a suggestion of M2
crypt development.
SK 62 (Table 1;Fig. 5a-c). SK 62 is part of
an immature mandible with 11, dc, dp3, and
dp4 on the right side and I1 (unerupted),di2,
dc, dp3, dp4, and unerupted M1 and M2 on
the left side (see Figs. 3-5 in Conroy and
Vannier, 1991). The following results are
based on a contiguous series of 31 parasagittal CT scans taken at 1mm intervals.
The crowns and roots of the left deciduous
canine and deciduous lateral incisor are
clearly visualized in several scans. The deciduous canines still have about 10 rnm and
the di2 about 4 mm of root preserved (Figs.
5a,b).
Enamel thickness is worn to less than
1mm in dp3 and to about 1 mm in dp4. Both
have about 8 mm of root preserved (Fig. 5a).
Permanent incisor crown formation is
complete and root development is well established. Left I2 and I1 crown heights are
estimated at 8-9 mm and root lengths at
5 mm. The root length of the RI1 is estimated
at 6-7 mm (Fig. 5c). It is arguable whether
the RIl has truly emerged (Skinner and
Sperber, 1982) or if its position is an artifact
140
G.C. CONROY AND M.W. VANNIER
STAGE!
INCISOR5 ZANINC
PREMOLAR!
MOLARS
1.2
1
0
1
2
3
-0,
4
5
6
7.7
7
n
,
Q
3
DENTAL STAGE ASSESSMENT
of preservation (Wallace, 1977). Whatever
the case, there is no wear on its occlusal
surface. The incisors are scored at dental
stage 5 .
Enamel formation on the permanent canine seems complete down to the cementoename1 junction. Crown height is about
9mm. Root initiation may have just commenced. The permanent canine is forming
right at the base of the mandibular corpus
(Fig. 5b). This tooth is scored a t dental stage
4.
Enamel formation on P3 is approaching
the cementoenamel junction; there is no indication of root development. Crown length
is estimated at 9-10 mm and crown height
about 5 mm. This tooth is scored at dental
stage 4 (Fig. 5a).
The P4 is less developed in that enamel
formation is complete a t the occlusal surface
with some extension toward the cervical region. There is no root development. Crown
Fig. 1. Description of dental formation stages (based
on Demirjian et al., 1973; Fleagle and Schaffler, 1982).
Stages: 0: No calcification present. 1: In both uniradicular and multiradicular teeth, a beginning of calcification
is seen a t the superior level of the crypt in the form of an
inverted cone or cones. There is no fusion of these
calcified points. 2: Fusion of the calcified points forms
one or several cusps that unite t o give a regularly
outlined occlusal surface. 3 a) Enamel formation is
complete a t the occlusal surface. Its extension and convergence toward the cervical region is seen. b) The
beginning of a dentinal deposit is seen. c) The outline of
the pulp chamber has a curved shape at the occlusal
border. 4: a) The crown formation is completed down to
the cementoenamel junction. b) The superior border of
the pulp chamber in uniradicualr teeth has a definite
curved form, being concave toward the cervical region.
The projection of the pulp horns, if present, gives an
outline like an umbrella top. In molars, the pulp chamber
has a trapezoidal form. c) Beginning of root formation is
seen in the form of a spicule. 5: Uniradicular teeth-a)
The walls of the pulp chamber now form straight lines,
whose continuity is broken by the presence of the pulp
horn, which is larger than in the previous stage. b) The
root length reaches a t least one-third of crown height.
Molars-a) Initial formation of the radicular bifurcation
is seen in the form of either a calcified point or a
semilunar shape. b) The root length is still less than the
crown height. 6 Uniradicular teeth-a) The walls of the
pulp chamber now form a more or less isosceles triangle.
The apex ends in a funnel shape. b) The root length is
equal to or greater than the crown height. Molars-a)
The calcified region of the birfucation has developed
further down from its semilunar stage to give the roots a
more definite and distinct outline, with funnel-shaped
endings. b) The root length is equal to or greater than the
crown height. 7: a) The walls of the root canals are now
parallel (distal root in molars). b) The apical ends of the
root canal are still partially open (distal root in molars).
8: a)The apical end of the root canal is completely closed
(distal roots in molars).
142
G.C. CONROY AND M.W.VANNIER
Fig. 2. SK 438: 1 mm CT slice through emerging dp,
and developing M,.
length is estimated a t 8 mm. The P4 is rotated so that its occlusal surface faces distally. This is presumably a mechanism to
save mesiodistal space in the developing
mandible of large-toothed hominids. P4 is
scored between dental stages 2 and 3 (see
Fig. 4 in Conroy and Vannier, 1991).
Enamel formation on the unerupted M1
crown is complete. Crown length is about
13-14 mm, crown height about 7 mm, and
root length about 6 mm. Enamel thickness is
estimated at 2 mm. This tooth is scored at
dental stage 6 (see Fig. 4 in Conroy and
Vannier, 1991).
Enamel formation on the M2 is complete
at the occlusal surface, with some extension
toward the cervical region. Its crown length
is estimated a t 12-13 mm. This tooth is
scored between dental stages 2 and 3 (see
Fig. 4 in Conroy and Vannier, 1991).
SK 61 (Table 1). SK 61 is part of an immature mandible with left and right d i l , di2, dc,
dp3, dp4, and erupting right M1. The following results are based on a contiguous series
of 27 parasagittal CT scans taken at 1mm
intervals and a contiguous series of 29
parasagittal CT scans taken at 2 mm intervals (see Figs. 7-9 in Conroy and Vannier,
1991).
Enamel thickness on the dp4 is slightly
greater than on the dp3, but both are around
1 mm. Root lengths on both teeth are about
7-8 mm.
Crown formation of the permanent incisors is complete to the cementoenamel junction, and root development is established.
Central incisor crown height is approximately 8 mm and root length approximately
4 mm. The occlusal edges of the left I1 and I2
are about 2 and 5 mm, respectively, from the
alveolar plane. The gubernacular canals for
both incisors are visible. Both incisors are
scored a t dental stage 5.
Crown development of the permanent canine is complete to the cementoenamel junction, but there is no indication of any root
development as yet. Crown height is approximately 9 mm. This tooth is scored at dental
stage 4.
Crown development of the P3 is nearing
completion toward the cementoenamel junction and is scored at dental stage 4. Enamel
formation of the P4 is complete a t the occlusal surface, with extension toward the
cervical region. It is scored at dental stage 3.
Neither premolar has any root development
as yet. Maximum crown length of each is
about 10-11 mm. Note the rotation of the
developing P3 and P4 so that the occlusal
surfaces are facing posterosuperiorly at an
angle of about 30" to the occlusal surfaces of
the deciduous premolars.
The emerging M1 has completed crown
development to the cementoenameljunction.
Rooth length and crown height are estimated at 7 mm. Enamel thickness is approx-
DENTAL STAGE ASSESSMENT
Fig. 3. SK 64. a: 1 mm CT slice through dp,, dp,, and
developing M,. Note initial calcification of P, and ab-
143
sence of P, calcification. b: Note developing MI and
possible M, crypt formation.
Fig. 4. SK 3978. a: 1 mm CT slice through dp, and dp,. Note root of d, and initial calcification of P,. b:
Note roots of di, and d, and development stage of the canine. c: Note development stage of I, and I,. A small
amount of di, root is visible. d: Note development stage of M, and possible crypt formation for M,.
DENTAL STAGE ASSESSMENT
imately 2 mm. This tooth is scored a t dental
stage 6.
SK 63 (Table 1;Fig. 6a-d). SK 63 is part of
an immature mandible preserving left and
right dc, dp3, dp4, and M1. Still unerupted
are the RI1, R12, L12, LC, and left and right
M2. The following results are based on a
contiguous series of 36 parasagittal CT scans
taken at 1 mm intervals.
Root lengths on dp3 and dp4 are about 5
and 9 mm, respectively (Fig. 6a).
Crown formation of the permanent incisors is complete, and roots are well established. Crown heights of I1 and I2 are about
9 mm. Only about 2-3 mm of the broken-off
roots are preserved on the right I1 and left I2
(Fig. 6b,c). Incisors are scored at dental stage
5-6? (the question mark denotes uncertainty
because of root breakage).
Crown formation is nearing completion in
the permanent canines, but no root has been
formed. Crown height is about 8 mm (Fig.
6d). This tooth is scored at dental stage 4.
Crown formation is also nearing completion in the P3 (stage 4). Enamel formation is
complete at the occlusal surface of P4, with
extension and convergence toward the cervical region (stage 3). Neither premolar has
any root development. Their crown lengths
are about 10mm. Note again the counterclockwise rotation of the P4 (Fig. 6d).
M1 has just recently come into occlusion.
Root length is about 8mm, crown height
about 7mm, and enamel thickness about
2 mm. This tooth is scored between dental
stages 6 and 7 (Fig. 6a).
Enamel formation is complete at the occlusal surface of M2. Some extension and
convergence of enamel toward the cervical
margin is seen, as are the beginnings of
dentinal deposition. Its crown length is estimated at 13 mm (Fig. 6a). It is scored a t
dental stage 3.
Australopithecus africanus
Sts 2 (Table 1;Fig. 7a,b). Sts 2 is a facial
fragment of an immature individual preserving the left dp3, dp4, and dc and the right
dp3, dp4, and unerupted canine. The following results are based on a series of 9 contiguous CT scans taken at 2 mm intervals.
Both deciduous premolars are worn, but
enamel thickness is greater on dp4. Root
length of the dp4 is estimated at 7 mm (Fig.
7a).
Enamel formation of P3 is not well visualized but appears complete at the occlusal
145
surface, with some extension toward the cervical margin (stage 3). Initial dentinal deposition is apparent. The P4 is less well developed, although calcification has progressed
to the point where a regular outline to the
occlusal surface can be seen (stage 2). No
dentinal deposition is visable (Fig. 7b).
The unerupted M1 crown is completely
formed down to the cementoenamel junction.
Faint markings for initial radicular bifurcation are evident. M1 length is estimated at
12 mm, and its surface is rotated some 5060" from the occlusal plane. Its mesial surface is only about 1 mm from the alveolar
margin. Enamel thickness at the midpoint of
the tooth is estimated a t 2 mm. It is scored at
dental stage 5 (Fig. 7a).
There is no evidence of M2 calcification.
Taung 1 (Table 1). The Taung skull preserves the upper and lower jaws containing
the erupted deciduous incisors, canines, premolars, and permanent first molars on each
side (see Figs. 11, 12, 16, and 17 in Conroy
and Vannier, 1991).The followingdiscussion
is based on 40 contiguous CT scans taken at
1mm intervals.
Root lengths for the lower deciduous teeth
are estimated as follows: di = 6 mm, dc
= 8 mm, dp3 = 5 mm; and dp4 = 7 mm. The
enamel is worn very thin on both deciduous
premolars.
The crowns of the permanent incisors and
canines are nearing completion. There is
little, if any, root development on the incisors
and canines. Permanent upper and lower
central incisor crown heights are estimated
at 10-11 mm. Incomplete upper and lower
canine crown heights are about 8-9 mm.
Incisors and canines are scored at dental
stage 4.
The permanent upper and lower premolars show complete formation of the occlusal
surface with some extension and convergence toward the cervical region. Dentinal
deposition is seen below the enamel crown.
P3 development is slightly more advanced
than that of P4. No root formation is present
in any of the permanent premolars. P3 is
scored between dental stages 3 and 4; P4 is
scored at stage 3.
The mesial borders of the recently emerged
first molars have only just reached the occlusal plane. Crown formation is complete.
Crown height and root length of the lower
M l s are both about 5-6 mm. Root length is
slightly less on the upper Mls. Enamel thickness is estimated a t 1-2 mm. The upper M1
146
G.C. CONROY AND M.W. VANNIER
DENTAL STAGE ASSESSMENT
is rotated about 35" from the occlusal plane
and the M2 about 80-90". The M2 is scored at
dental stage 6.
The occlusal surface of the upper M2 appears to be complete and is approximately
10-1 1mm in length (stage 2).
In general, development of the lower dentition is slightly in advance of the upper
dentition.
Sts 24 (Table 1; Fig. 8a,b). This individual
is a composite of upper and lower deciduous
and permanent teeth of an immature australopithecine previously catalogued as Sts
24/69/70 Grine (1981) (See Fig. 13 in Conroy
and Vannier, 1991). The followingdiscussion
is based on a series of 23 contiguous CT scans
taken at 2 mm intervals.
Based on the emergence status of M1 and
the small amount of root development on the
lower incisors, this specimen is judged to be
slightly older than the Taung specimen,
which it otherwise resembles quite closely.
The crowns of both upper and lower incisors are complete. Root development had
just begun on the upper central incisors but
not on the upper lateral incisors. There is
about 2 mm of root development on the lower
incisors. The absence of wear and rudimentary development of the roots indicate that
the incisors had not erupted. In fact, the
lower deciduous central incisors still have
some 10-12 mm of root preserved, suggesting that resorption had not progressed very
far (Conroy and Vannier, 1991). Incisors are
scored between dental stages 4 and 5.
Enamel formation of the upper canine is
complete at the occlusal surface and is approaching the cementoenamel junction.
There is no root development present. It is
scored at dental stage 4 (Fig. 8a).
Development of the premolar teeth is similar to that previously described €or the
Taung specimen. Dentinal deposition is seen
on P3 and, to a lesser degree, on P4. P3 is
scored between dental stages 3 and 4; P4 is
scored at stage 3 (Fig. 8b).
The first molars show slight amounts of
occlusal wear. Enamel thickness is about
2 mm. Crown development is complete, but
because of the breakage in the specimen root
length is not well visualized. It appears that
the tooth had advanced beyond the initial
Fig. 5. SK 62. a: 1 mm CT scan through d,, dp,, dp,,
and MI.C, canine. b Note development stage of the
permanent canine (0.c: Note development stage of RI,.
147
radicular bifurcation phase. It is scored at
stage 6.
Calcification of the occlusal surface of M2
is complete (stage 2).
Sts 18 (Table 1; Fig. 9a,b). Sts 18 is a
mandible preserving the right dp3, dp4, M1,
and unerupted M2, and left dp4 and M1. The
following discussion is based on a series of 23
contiguous CT scans taken at 2 mm intervals.
The dp4 still has about 7 mm of root preserved (Fig. 9a).
Enamel surfaces on the P3 and P4 are
complete at the occlusal surface and extend
and converge toward the cervical region.No
root formation is evident. Development of P3
is slightly in advance of P4. Crown length of
P3 is estimated at 9 mm and P4 at 11mm
(Fig. 9b). P3 is scored a t dental stage 4; P4 is
scored between dental stages 3 and 4.
There is occlusal wear on M1. Enamel
thickness of M1 is estimated at 2 mm and
root length at 9mm. The tooth is scored
between dental stages 6 and 7.
Crown development is nearing completion
on M2. There is no root development on this
tooth (Fig. 9a). It is scored at dental stage 4.
MLD 2 (Table 1). This specimen is an
immature mandible containing the left P3,
dp4, M1, M2 and the right P3, P4 (erupting),
M1, and M2 (see Fig. 18a in Conroy and
Vannier, 1991). The following discussion is
based on 31 contiguous CT scans taken at
1 mm intervals.
The developing canine crown is complete,
and substantial root is evident. Canine
crown height is estimated at 11mm and root
length at 10mm. This tooth is scored between dental stages 5 and 6.
The P3s had recently erupted, and their
root lengths are about 5-6 mm. Root length
of the unerupted P4s are about the same. P3
is scored at dental stage 6; P4 is scored at
stage 5.
There is occlusal wear on the first molars.
Enamel thickness is about 2 mm at the midpoint of the tooth, and root length is about
8 mm. MI is scored at dental stage 7.
The erupted M2s have about 6 mm of root
formed. They are scored at dental stage 6.
Sts 8 (Table 1; Fig. 10a,b). Sts 8 is a left
maxilla preserving M1, M2, and unerupted
M3. The following discussion is based on
nine contiguous CT scans taken at 2 m m
intervals.
Root lengths on M1 and M2 are estimated
at 10 mm and enamel thickness at 2 mm.
Fig. 6. SK 63. a: 1 mm CT slice through the dp,, dp,, MI, and M,. b: Note developmental stage of I,. c:
Note developmental stage of I,. d Note rotation of P, crown.
DENTAL STAGE ASSESSMENT
149
Fig. 7. Sts 2. a: 2 mm CT slice through dp4 and M'. b: Note developmental stages of P3 and I"'.
The apical end of the root canal on M2 is still
partially open (Fig. 10a). M1 and M2 are
scored between dental stages 7 and 8.
The crown of M3 is complete down to the
cementoenamel junction. No root formation
is evident. Its occlusal surface is oriented
some 80" from the occlusal plane (Fig. lob). It
is scored at dental stage 4.
Stw 327 (Table 1). This specimen is a
portion of a mandible with P4-M2. (see Fig.
18b in Conroy and Vannier, 1991). The fol-
lowing discussion is based on a contiguous
series of 27 CT scans taken at 1mm intervals.
The P4-M1 have reached the occlusal
level, but only the mesial half of the M2 has
reached the occlusal plane. Judging by the
occlusal wear patterns and root development, P4 preceeded M2 in emergence, unlike
the sequence noted below for MLD 2. Root
lengths of P4-M2 are estimated at 12, 11,
and 8 mm, respectively.
150
G.C. CONROY AND M.W. VANNIER
Fig. 8. Sts 24. a: 2 mm CT slice through dp4 and M'. Note developmental stage of the canine. b: Note
developmental stage of the and P.
P4 is scored at dental stage 7, M1 between
stages 7 and 8, M2 at stage 8, and M3 at stage
4.
Crown formation of the unerupted M3 is
approaching the cementoenamel junction.
No root formation is present as yet.
DISCUSSION
A. robustus
The six immature A. robustus individuals
represent a small cross-sectional sample of
the developing dentition in this species. The
age of death of SK 438 has been previously
estimated at 1.5-2.5 years based on human
dental standards (Mann, 1975;Brain, 1981)
and 1.0 year based on pongid dental standards (Bromage, 1987). The Paranthropus
dental chronology of Beynon and Dean
(1988) suggests an age between 1.0 and 1.5
years. The fact that P4 calcification had not
yet begun indicates an age less than 2.5
years regardless of the dental standards
used. While dental maturation may have
occurred relatively rapidly in SK 438 (i.e.,
DENTAL STAGE ASSESSMENT
151
Fig. 9. Sts 18. a: 2 mm CT slice through MI and M,. b: Note developmental stages of P, and P,.
following a chronology more similar to
pongids than to humans), it is still open to
question whether theputtern of development
was pongidlike as well (see Conroy and Vannier, 1991). Both M1 maturation and dp4
root length are further advanced at the time
of dp4 emergence in humans compared with
apes (Dean and Wood, 1981). These features
relate to the fact that dp4 emerges later in
humans than in apes. In both these features,
SK 438 more closely resembles the humanlike pattern. Thus, if the Puranthropus chro-
nology of Beynon and Dean (1988) is correct,
this humanlike pattern is superimposed on a
pongidlike chronology.
The age of death of SK 64 has been previously estimated a t 2-3 years based on both
human and pongid dental standards (Brain,
1981; Skinner and Sperber, 1982; Bromage,
1987). The Puranthropus dental chronology
of Beynon and Dean (1988) suggests an age
of 1.0-2.0 years. Evidence of a more humanlike dental pattern is clearer in SK 64 than in
SK 438 because of the added information on
152
G.C. CONROY AND M.W. VANNIER
Fig. 10. Sts 8. a: 2 mm CT slice through M',
Note absence of root development on M3.
M2,and M3.Note developmental stages of the molars. b:
the calcification of P3. In the pongidlike
pattern there is a delay of approximately
1.0-1.5 years between the emergence of dp4
and the initial calcification of P3. In the
humanlike pattern these two events occur
within a relatively brief time span (Dean and
Wood, 1981). This relationship in SK 64 is
more reminiscent of the human condition.
The presence of possible M2 crypt formation
is also compatible with the humanlike pattern, since dp4 emergence and initiation of
M2 calcification also occur within a relatively brief time span. In the pongidlike pattern these two events may be delayed by 1-2
years. If the Paranthropus chronology of
Beynon and Dean (1988) is correct, this humanlike pattern is superimposed on a chronology that develops even more rapidly than
in modern pongids.
The age of death of SK 3978 has previously
been estimated at approximately 2.0-3.0
years based on both human and pongid den-
DENTAL STAGE ASSESSMENT
tal standards (Brain, 1981; Skinner and
Sperber, 1982; Bromage, 1987). The Paranthropus chronology of Beynon and Dean
(1988) suggests an age of 1-2 years. The
observations on dental pattern noted above
for SK 64 also apply to SK 3978. As in SK 64,
the dp4 must have recently emerged since
there is little, if any, occlusal wear present.
In a pongidlike pattern, canine and incisor
development would be rudimentary a t or
near dp4 emergence time, whereas in a humanlike pattern they would be further developed (Dean and Wood, 1981). SK 3978 conforms more to the humanlike pattern in
these relationships. This reinforces the suggestion made above that a humanlike pattern has been superimposed on a pongidlike
chronology.Again, if the Paranthropus chronology of Beynon and Dean (1988) is correct,
this humanlike pattern is superimposed on a
chronology that develops even more rapidly
than in modern pongids.
The age of death of SK 62 has previously
been estimated at 5.7-6.0 years based on
human dental standards (Skinner and Sperber, 1982)and 3.3-3.5 years based on pongid
dental standards and perikymata counts
(Bromage, 1987; Bromage and Dean, 1985).
The Paranthropus chronology of Beynon and
Dean (1988)suggests an age of 2.5-3.0 years.
The presence of both incisor root formation
and nearly complete premolar crowns at or
before the time of first molar eruption in SK
62 is characteristic of the humanlike development pattern. In the pongidlike pattern
the first molars erupt early before there is
time for incisor roots or premolar crowns to
develop to the same extent (Dean and Wood,
1981). The probable initiation of canine root
development also points to a more humanlike pattern, since canine crown completion
is delayed relative to M1 emergence in the
pongidlike pattern. Again, if the Paranthropus chronology of Beynon and Dean (1988)is
correct, this humanlike pattern is superimposed on a chronology that develops more
rapidly than in modern pongids.
The observations noted above for SK 62
also pertain to SK 61, although incisor root
development has not progressed as far relative to M1 emergence stage. Presumably this
reflects a degree of intraspecific variation in
these parameters (Conroy and Vannier,
1991). The age of death of SK 61 has previously been estimated at about 6 years based
on human dental standards (Brain, 1981;
Skinner and Sperber, 1982) and 3.3 years
based on pongid dental standards (Bromage,
153
1987). An age of around 3 years is inferred
from the Paranthropus chronology of Beynon and Dean (1988).
The age of death of SK 63 has previously
been estimated a t about 6 years based on
human dental standards (Brain, 1981; Skinner and Sperber, 1982) and 3.3 years based
on pongid dental standards (Bromage, 1987;
Smith, 1986). An age of around 3 years is
inferred from the Paranthropus dental chronology of Beynon and Dean (1988) and Dean
(1988). As in SK 62 and SK 61, the presence
of both incisor root formation and well-developed premolar crowns a t the time of first
molar eruption in SK 63 is characteristic of
the humanlike development pattern. The
near completion of canine crown development at M1 emergence also points to a more
humanlike pattern, since canine crown formation is delayed relative to M1 emergence
in the pongidlike pattern. The developmental status of the first molar suggests that this
tooth emerged relatively early in its developmental cycle, because its roots are still only
about equal in length to crown height (stage
6 ) even though it had already reached the
occlusal plane. In modern humans, M1 does
not usually emerge until stage 7 at which
point root length is greater than crown
height (Demirjian and Levesque, 1980).
These immature A. robustus individuals
represent a small cross-sectional sample of
the developing dentition in this species that
can be conveniently divided into two age
classes: 1)SK438,SK64, SK3978; and2)SK
62, SK 61, SK 63. If one individual is selected
from each age class (e.g., SK 3978 and SK63)
they would sample the robust australopithecine dentition at very different ages, depending on which dental standard is used. For
example, the ages would be approximately
2.5 and 6.0 years using human standards,
2.5 and 3.3 years using pongid standards, or
1.5 and 3.0 years using perikymata standards (the basis for the australopithecine
ages in Table 1).Dental development would
have occurred over an interval of about 3.5
years in the first case, about 1 year in the
second case, or about 1.5 years in the third
case. During this interval the canine developed through at least one developmental
stage; 11, 12, and P3 through at least two
stages; and P4, M1, and M2 (inferred from
SK 64) through a t least three stages (Table
1).
If a pongidlike pattern of dental development is considered the primitive hominoid
condition, then a derived humanlike pattern
154
G.C. CONROY AND M.W. VANNIER
can be developed in one of two ways: 1)by
accelerating the maturation of antemolar
teeth relative to molars or 2) by delaying
maturation of molars relative to antemolar
teeth. Acceptance of the perikymata chronology of Beynon and Dean (1988) and the
dental development data provided here support the view that humanlike robust australopithecine dental patterns resulted from the
first process, whereas modern human patterns clearly resulted from the second process. In a sense, then, the similar patterns
found between A. robustus and humans are
best considered convergences rather than
parallelisms.
A. africanus
The seven specimens ofA. africanus represent a small cross-sectional sample of the
developing dentition in gracile australopithecines.
The age of death of Sts 2 has previously
been estimated a t about 5 years based on
human dental standards (Brain, 1981; Skinner and Sperber, 1982) and 3.5 years based
on pongid dental standards (Bromage,
1987).An age of between 2.5 and 3.0 years is
inferred from the Australopithecus chronology of Beynon and Dean (1988). Since initial
M2 calcification occurs around the age of 2.5
years in apes and 3.5 years in humans (Dean
and Wood, 1981; Berkovitz et al., 1984;
Smith, 19911, its apparent absence in Sts 2
would particularly mitigate against the age
estimate based on the human standards.
The pattern of development seems consistent with an age of around 2.5-3.0 years
irrespective of the dental standards used.
The age of the Taung child has been estimated at about 4.5-6.0 years based on human standards (Skinner and Sperber, 1982;
Wolpoff et al., 1988; Mann, 1988; Mann et
al., 1987) and about 3.5 years based on
pongid standards (Conroy and Vannier,
1987,1988,1989;Bromage, 1987).The latter
age is consistent with the Australopithecus
chronologyof Beynon and Dean (1988). Comparison of these data with those of mean
chronological calcification and emergence
times of the developing dentition in modern
apes and humans reveals that, overall, the
Taung specimen is most comparable to a
pongidlike pattern. Human lower first molars and central incisors usually emerge
within a relatively brief time span, whereas
in pongids the first molars emerge about 2
years before central incisors (Conroy and
Mahoney, 1991). Thus the pongidlike pattern is characterized by 1j little or no resorption of deciduous incisor roots at first molar
emergence; 2) permanent incisors that are
still low in their alveolar crypts at first molar
emergence; 3) permanent incisors, canines,
and premolars that have little, if any, root
development at first molar emergence; and
4) first molars that emerge at dental stage 6,
i.e., with root length about equal to crown
height. The Taung dentition clearly reflects
these conditions.
The age of death of Sts 24 has previously
been estimated at around 5.0-7.0 years
based on human standards (Brain, 1981)
and around 3.3 years based on pongid standards (Bromage and Dean, 1985; Smith,
1986). An age of 3.5-4.0 years is inferred
from the Australopithecus chronologyof Beynon and Dean (1988).The pongidlike pattern
discussed above for the Taung skull applies
to Sts 24 as well.
The age of death of Sts 18 has been previously estimated at about 7.2 years based on
human standards (Skinner and Sperber,
1982) and at 5.25 years based on pongd
standards (Bromage, 1987).An age of about
4.5-5.0 years is inferred from the Australopithecus chronology of Beynon and Dean
(1988).The developmental status of the premolars and molars is consistent with a
pongidlike, pattern. In this pattern, crawn
completion of P3, P4, and M2 occurs within a
relatively brief time period (Dean and Wood,
1981). In the humanlike pattern, root formation would be expected on the P3 and P4 a t
the time of M2 crown completion because of
the delay in the latters development.
The age of death of MLD 2 has previously
been estimated at about 11.3years based on
human dental standards (Skinner and Sperber, 1982) and 6.6 years based on pongid
dental standards (Bromage, 1987). This latter age is consistent with the Australopithecus chronology of Beynon and Dean (1988).
The sequence of dental eruption is interesting in this specimen. The dental eruption
sequence in pongids is normally M1 I1 I2 M2
[P3 P41 C M3; the usual pattern in humans
(mandibular dentition) is [Ml I13 I2 [C P31
[P4 M21 M3 (brackets indicate variability in
the sequence greater than or equal to 20%)
(Smith and Garn, 1987; Schultz, 1935,1940;
Nissen and Riesen, 1964; Conroy and Mahoney, 1991). Thus in humans the canine
(and often the P4j erupts before the M2, but
155
DENTAL STAGE ASSESSMENT
in pongids both teeth usually erupt after the
M2. MLD 2 is clearly pongidlike in this feature.
The age of death of Sts 8 has previously
been estimated at 13.0 years based on human dental standards (Skinner and Sperber,
1982) and 7.75 years based on pongid dental
standards (Bromage, 1987). The latter age is
consistent with the Australopithecus chronology of Beynon and Dean (1988).
Stw 327 would be aged about 13.0-14.0
years based on human dental standards or
about 8.0 years based on pongid dental standards. An age of between 7.0 and 8.0 years is
inferred from the Australopithecus chronology of Beynon and Dean (1988).
If two A. africanus individuals are selected
from different age groups (e.g., Taung and
MLD 21, they would sample the gracile australopithecine dentition at very different
ages depending on which dental standard is
used. For example, the ages would be approximately 5.0 and 11.0 years using human
standards or 3.5 and 6.6 years using both
pongid and perikymata standards. Dental
development would have occurred over an
interval of about 6.0 years in the first case or
about 3 years in the second case. During this
interval the canine and M1 developed
through a t least one developmental stage; P3
and P4 through a t least two stages; and M2
through at least four stages (Table 1).
As noted earlier, two issues concerning
australopithecine dental development have
become particularly controversial: 1) are
dental development patterns distinctive between A. robustus and A. africanus and 2)
are dental development chronologies distinctive between australopithecines and modern
humans? Table 1 provides data germane to
these issues.
We have noted that where humanlike and
pongidlike dental patterns can be differentiated in the specimens examined here, the A.
robustus individuals are usually more compatible with the humanlike pattern and the
A. africanus specimens with the pongidlike
pattern. This is most evident in Il/Ml developmental relationships. While this assessment is equivocal in some specimens and a t
certain ages, the general trend is reasonably
inferred from the data. This seems to be true
even in those specimens such as SK 64 and
SK 3978 that are given a similar chronological age based on either human or pongid
dental standards.
At the present time, the absolute chrono-
logical age for any given fossil specimen can
only be estimated by perikymata counts, and
these indicate a rapid maturation rate for
australopithecine teeth (Dean, 1987;Beynon
and Dean, 1988). Is there any corroborating
evidence for rapid dental maturation rates
from the data presented here? It appears
that there is. Australopithecine teeth seem
to emerge and reach occlusion at a relatively
early stage in their growth cycle. For example, first molars emerge by stage 6 (SK 61,
Taung, Sts 24); central incisors by stage 5
(SK 62); and third premolars by stage 6
(MLD 2). Data from a sample of over 5,000
French-Canadian children indicate that the
permanent teeth in modern humans normally emerge around dental stage 7 (Demirjian and Levesque, 1980). (Unfortunately,
similar data do not exist for non-European
populations). When first molars are emerging at stage 7 in the modern human sample,
permanent incisors have already reached
stage 6, canines stage 5, third premolars
stage 5 , fourth premolars stage 4, and second
molars stage 4. From Table 1 it is apparent
that australopithecine first molars emerge
relatively early compared with the other
teeth, since the permanent incisors have
only reached stages 4-5, the canines and the
third and fourth premolars stages 3-4, and
the second molars stages 2-3.
These data on crown and root formation,
taken together with the chronologies of Beynon and Dean (1988), provide unique information regarding the timing and pattern of
dental maturation in gracile and robust australopithecines.
ACKNOWLEDGMENTS
We are deeply indebted to Prof. Phillip
Tobias of the University of the Witwatersrand and Drs. C.K. Brain and V. Watson
of the Transvaal Museum for their cooperation and support during this project and for
permitting us to obtain CT images of fossil
material in their care. To them and their
staff, we are most grateful. It has been a
pleasure to work with the radiographers of
Hillbrow Hospital, Johannesburg: R. van der
Riet, I. Amla, F. Gora, and R. Harman. Discussions with Drs. c. Dean and D. Beynon
are gratefully acknowledged as are the helpful comments of two anonymous reviewers.
Finally, G.C.C. thanks Mr. and Mrs. S. and
B. Suzman, whose hospitality made all the
difference. This research was supported by a
grant from the National Science Foundation
156
G.C. CONROY AND M.W. VANNIER
and by a Fulbright Senior Scholar Research
Award (G.C.C.).
LITERATURE CITED
Berkovitz BKB, Holland GR, and Moxham BJ (1984)
Oral Anatomy. Holland: Wolfe Medical Publications
Ltd.
Beynon AD, and Dean MC (1988) Distinct dental development patterns in early fossil hominids. Nature
335:509-514.
Brain CK (1981) The Hunters or the Hunted. Chicago:
University of Chicago Press.
Bromage T (1987)The biological and chronological maturation of early hominids. J. Hum. Evol. 161257-272.
Bromage TG, and Dean MC (1985) Re-evaluation of the
age at death of immature fossil hominids. Nature
317:525-527.
Broom R, and Robinson J T (1951)Eruption ofthe permanent teeth in the South African fossil ape-man. Nature
167:443.
Conroy GC (1988) Alleged synapomorphy of the MU11
eruption pattern in robust australopithecines and
Homo: Evidence from high-resolution computed tomography. Am. J. Phys. Anthropol. 75:487-492.
Conroy GC, and Mahoney CJ (1991)A mixed longitudinal study of dental emergence in the chimpanzee, Pan
troglodytes. Am. J. Phys. Anthropol. (This issue).
Conroy GC, and Vannier MW (1987)Dental development
of the Taung skull from computerized tomography.
Nature 329:625-627.
Conroy GC, and Vannier MW (1988) The nature of
Taung dental maturation continued. Nature 333t808.
Conroy GC, and Vannier MW (1989) The Taung skull
revisited New evidence from high-resolution computed tomography. S. Afr. J . Sci. 8530-32.
Conroy GC, and Vannier MW (1991)Dental development
in South African australopithecines. Part I: Problems
of pattern and chronology. Am. J. Phys. Anthropol.
(This issue).
Dean MC (1985) The eruption pattern of the permanent
incisors and first permanent molars in Austrulopithecus (Puranthropus) robustus. Am. J. Phys. Anthropol.
671251-258.
Dean MC (1987) Growth layers and incremental markings in hard tissues: A review of the literature and
some preliminary observations about enamel structure in Parunthropus boisei. J . Hum. Evol. 16t157172.
Dean MC (1988) Growth of teeth and development of the
dentiton in Puranthropus. In FE Grine (ed.): Evolutionary History of the “Robust” Australopithecines.
New York: Aldine de Gruyter, pp. 43-54.
Dean MC and Wood BA (1981)Developing pongid dentition and its use for ageing crania in comparative
cross-sectional growth studies. Folia Primatol.
36~111-127.
Demirjian A (1979) Dental development: A measure of
physical maturity. In FE Johnson, AF Roche, and C
Susanne (eds.): Human Physical Growth. New York:
Plenum, pp. 83-100.
Demirjian A (1986) Dentition. In F Falkner and JM
Tanner (eds.): Human Growth. New York: Plenum,
vol. 2, pp. 269-295.
Demirjian A, Goldstein H, and Tanner JM (1973)A new
system of dental age assessment. Hum. Biol. 45~211227.
Demirjian A, and Levesque GY (1980)Sexual differences
in dental development and prediction of emergence. J.
Dent. Res. 59:lllO-1122.
Fleagle JG, and Schaffler MB (1982) Development and
eruption of the mandibular cheek teeth in Cebus ulbifrom. Folia Primatol. 38:158-169.
Garn SM, Koski K, and Lewis AB (1957) Problems in
determining the tooth eruption sequence in fossil and
modern man. Am. 3. Phys. Anthropol. 15:313-331.
Garn SM, and Lewis AB (1963) Phylogenetic and intraspecific variations in tooth sequence polymorphisms. In: DR Brothwell (ed.): Dental Anthropology.
Oxford: Pergamon, pp. 53-73.
Grine FE (1981) A new composite juvenile specimen of
Australopithecus africunus from Member 4 Sterkfontein Formation, Transvaal. Ann. S. Afr. Mus. 84:169201.
Grine FE (1987) On the eruption pattern of the permanent incisors and first permanent molars in Parunthropus. Am. J. Phys. Anthropol. 72:353-360.
Mann AE (1975) Some Paleodemographic Aspects of the
South African Australopithecines. Philadelphia: University of Pennsylvania Publications.
Mann AE (1988)Thenature ofTaung dental maturation.
Nature 333r123.
Mann AE, Lampl M, and Monge JM (1987)Maturational
patterns in early hominids. Nature 328:673-674.
Moorrees CF, Fanning EA, and Hunt EE (1963) Age
variation of formation stages for ten permanent teeth.
J . Dent. Res. 42:1490-1502.
Nissen HW, and Riesen AH (1964) The eruption of the
permanent dentition in the chimpanzee. Am. J. Phys.
Anthropol. 22t285-294.
Schultz AH (1935)Eruption and decay of the permanent
teeth in primates. Am. J. Phys. Anthropol. 19:489581.
Schultz AH (1940)Growth and development of the chimpanzee. Contrib. Embryol. 28:l-63.
Simpson SW, Lovejoy CO, Meindl RS (1990) Hominoid
dental maturation. J. Hum. Evol. 19:285-297.
Skinner MF, and Sperber GH (1982) Atlas of Radiographs of Early Man. New York: Alan R. Liss.
Smith BH (1986) Dental development in Austrulopzthecus and early Homo. Nature 323:327-330.
Smith BH (1989) Dental development a s a measure of
life history in primates. Evolution 43:683-688.
Smith BH (1991) Standards of human tooth formation
and dental age assessment. InM Kelley and CS Larson
(eds.): Advances in Dental Anthropology. New York:
Wiley-Liss pp. 143-168.
Smith BH, and Garn SM (1987) Polymorphisms in eruption sequence of permanent teeth in American children. Am. J. Phys. Anthropol. 74239-304.
Wallace J A (1977) Gingival eruption sequences of permanent teeth in early hominids. Am. J . Phys. Anthropol. 461483-495.
Weidenreich F 11937) The dentition of Sinunthropus
pekenensis: A comparative odontography of the hominids. Palaeonol. Sin. 1:120-180.
Wolpoff MH, Monge JM, Lampl M (1988) Was Taung
human or an ape? Nature 335501.
NOTE ADDED IN PROOF
More precise data on enamel thickness in
South African australopithecines are presented in Conroy, G.C. (1991)Enamel thickness in South African australopithecines:
Noninvasive evaluation by computed tomography. Palaeontol. africana (in press).
Документ
Категория
Без категории
Просмотров
1
Размер файла
3 074 Кб
Теги
development, part, africa, stage, dental, south, assessment, australopithecines
1/--страниц
Пожаловаться на содержимое документа