Comparative dental development and microstructure of ... - UCL

DENTAL DEVELOPMENT IN PROCONSUL
193
Table 6
Summary of crown completion times
Using perikymata Using enamel Using dentine Maximum value of means
Tooth type
P. nyanzae P. heseloni P. nyanzae P. heseloni P. nyanzae P. heseloni P. nyanzae P. heseloni
dm1 0·25 0·25
dm2 0·46 0·46
I1 2·5 2·4 2·5 2·4
I2 2·5 2·4 2·5 2·4
C 3·0–4·7 2·5 2·4 3·0–4·7 2·5
P3 1·8 1·8
P4 1·5 1·7 1·7 1·7
M1 1·8 1·0 1·9 1·2 2·0 1·2 2·0 1·2
M2 2·0 1·3 2·2 1·4 2·3 1·6 2·3 1·4
M3 1·7 1·7 1·7
Summary of data for crown formation times derived in three different ways in this study presented by tooth type.
(i) Perikymata counts combined with cuspal enamel formation times derived from the histological sections of each
tooth have been averaged for upper and lower teeth of the same tooth type. (ii) Estimates made from histological
sections only when tooth crowns were complete. (iii) Estimates made from counts and measurements of
incremental markings in dentine. In the last column the greatest values for crown formation times in both species
of Proconsul are summarized. The estimates that appear here for P. heseloni were used in the bar chart of dental
development (Figure 19).
development in Proconsul. The first is the
presence of both a strong and a fainter
accentuated line that recur in the enamel of
the P 4 and second M 2 of the adult P. heseloni
specimen and the same strong line in the
cervical enamel of the M 1 . These lines tie
these teeth together developmentally. The
second line of evidence comes from the
accentuated lines in the incisor tooth germs
and in the M 1 germ belonging to the infant
P. heseloni individual. The third line of evidence
comes from the distribution of linear
hypoplastic bands on the buccal enamel
surface of KNM-RU 7290. One strong band
with two fainter bands either side of it, can
be cross-matched across all the anterior
teeth, across the premolars and across the
M 2 s. The positions of these accentuated
lines within the enamel and of the hypoplastic
bands combined with the perikymata
counts on the surface of the teeth of
KNM-RU 7290 allow us to reconstruct a
preliminary sequence of tooth development
for P. heseloni from this specimen. The timing
of the initial mineralization of the third
molar is conjectural but we have simply
presumed here that it follows the pattern
and sequence known from histological
studies on dental development for certain
other primates where initial mineralization
overlaps with M 2 crown formation (Beynon
et al., 1991; Chandrasekera et al., 1993;
Reid & Dirks, 1997; Reid et al., 1998;
Swindler & Beynon, 1992) but this of course
may turn out not to be so in Proconsul.
Summary of the results
The following ten key points summarize the
results of this study. (i) Enamel thickness on
the lingual aspect of the permanent lower
incisor crowns in P. heseloni most resembles
that in extant New World monkeys and
hominoids and differs from that in extant
cercopithecoids in that it is not absent or
exceptionally thin. (ii) There is no evidence,
from this study that P. heseloni or P. nyanzae
had relatively thin molar enamel. The
measure of ‘‘relative enamel thickness’’ for
posterior teeth in P. heseloni and P. nyanzae
falls above and beyond the range previously
recorded for P. major and P. africanus,