A. D. Beynon
Department of Oral Biology,
The Dental School, University
of Newcastle upon Tyne,
NE2 4BW, U.K. E-mail:
a.d.beynon@newcastle.ac.uk
M. C. Dean*
Evolutionary Anatomy Unit,
Department of Anatomy &
Developmental Biology,
University College London,
Gower Street, London
WC1E 6BT, U.K.
E-mail: ucgacrd@ucl.ac.uk
M. G. Leakey
Department of Palaeontology,
Kenya National Museums,
P.O. Box 40658, Nairobi,
Kenya. E-mail:
palaeo@swiftkenya.com
D. J. Reid
Department of Oral Biology,
The Dental School, University
of Newcastle upon Tyne,
NE2 4BW, U.K. E-mail:
d.j.reid@newcastle.ac.uk
A. Walker
Department of Anthropology,
409 Carpenter Building,
The Pennsylvania State
University, University
Park, PA 16802-3404,
U.S.A. E-mail:
axw8@psu.edu
Received 10 July 1997
Revision received
1 March 1998
Accepted 12 March 1998
Comparative dental development and
microstructure of Proconsul teeth from
Rusinga Island, Kenya
Eighteen histological sections were prepared from eleven teeth attributed to Proconsul heseloni and two molar teeth attributed to Proconsul
nyanzae. Measurements of spacings and counts of daily incremental
markings in both enamel and dentine were possible in the majority of
these tooth sections. Measurements of the spacings and angles to the
enamel dentine junction (EDJ) of regular striae of Retzius and of
equivalent markings in dentine were also made. In addition to these
measurements, counts of perikymata were made on replicas of all
other Proconsul teeth housed in the National Museum of Kenya,
Nairobi, that preserved good perikymata on any aspect of their tooth
surface. The sequence of crown formation in Proconsul and the crown
formation times of the enamel and dentine were estimated from these
data. In addition, the rates of root extension were estimated using the
formula derived for this purpose by Shellis (Archs. oral Biol. 29,
697–705, 1984) and estimates of the total period of root formation
subsequently made for premolar and molar teeth based on measurements of root length. A composite chart of dental development for
P. heseloni is presented which suggests M3 root completion was
between six and seven years of age. In general Proconsul molar teeth
have high stria angles to the EDJ, a high ratio of enamel formed with
respect to dentine formed at the same time, median values of rates of
enamel formation close to the EDJ in excess of 4 ìm per day and the
occasional presence of ‘‘S-shaped’’ striae in the lateral enamel. There
is no evidence to suggest that Proconsul from Rusinga Island, Kenya,
had relatively thin enamel on molar or premolar teeth. When all of
these data are considered in a comparative context, Proconsul emerges
overall as hominoid-like in its enamel and dentine microstructure and
as most similar to Pongo but with some features shared with Pan and
Homo. Similar data for other Miocene primates will have considerable
bearing on how these data are interpreted. These new data on dental
microanatomy and on dental development in Proconsul make a further
contribution to our understanding of the total morphological picture
of this early Miocene primate.
1998 Academic Press
Keywords: Proconsul, Miocene
hominoids, enamel
thickness, Striae of Retzius,
enamel, dentine.
Journal of Human Evolution (1998) 35, 163–209
Article No. hu980230
Introduction
Proconsul is the best represented Early
Miocene fossil primate, and is widely
regarded as the earliest known hominoid.
*To whom all correspondence should be addressed.
0047–2484/98/070163+47$30.00/0
Evidence from the postcrania, however,
points to a complex mosaic of morphological characters, some of which have
been interpreted as hominoid-like, and
others of which have been interpreted as
basal catarrhine characters (Aiello, 1981;
1998 Academic Press
164
. . 
Beard et al., 1986; Begun et al., 1993;
Fleagle, 1983; Harrison, 1987, 1993; Lewis,
1971; Napier & Davis, 1959; Rose, 1997;
Ward et al., 1991, 1993). Overall, these
postcranial characters suggest Proconsul was
an arboreal quadruped with a varied positional repertoire that indulged in relatively
slow climbing but which showed few signs of
forelimb suspensory behaviour (Walker,
1997). Evidence from the skull and dentition includes characters that link Proconsul
with later hominoids. The estimated degree
of encephalization of P. heseloni, although
based on one specimen (KNM-RU 7290),
suggests that Proconsul had a bigger brain
than modern cercopithecoids of a comparable body mass (Walker et al., 1983). Other
craniodental features such as the presence of
a frontal air sinus (Walker & Teaford,
1989), a wide frontal bone at bregma, the
development of a maxillary jugum, a low
crowned P3 and reduced cusp heteromorphy
of the upper premolars are also each considered by some to be hominoid synapomorphies (Andrews, 1985). For a recent
review see Walker (1997).
Four species of Proconsul are now
described (Walker et al., 1993; Teaford
et al., 1993; Andrews, 1996). Proconsul
africanus and Proconsul major are known
from the type sites of Koru and Songhor in
western Kenya and P. major also from
Meswa Bridge in Kenya and Napak in
Uganda. P. heseloni and P. nyanzae are the
two species that are represented at Rusinga
and Mfangano Islands in Kenya (Walker
et al., 1993). Ruff et al. (1989) used crosssectional measurements of the femoral
diaphysis and articular dimensions to estimate the body weight of Proconsul specimens
from Rusinga and Mfangano. Rafferty et al.
(1995) subsequently made estimates from
ankle joint surface areas. Both estimates are
around 9–12 kg for the smaller P. heseloni
specimens (about the same as a siamang, or
twice that of smaller Hylobates species).
Body weight estimates for P. nyanzae are
ET AL.
closer to those of female chimpanzees of
the smallest subspecies averaging 35·6 kg
(Rafferty et al., 1995).
Reviewing the paleoecology and the
hominoid paleoenvironments, Andrews
(1996) presented evidence that Songhor and
Koru (dated at 19–20 Ma) have fossil faunas
which suggest environments closest to
tropical African, non-seasonal, wet, evergreen forest faunas today, whereas the
slightly younger (17·5–17·9 Ma) Rusinga
and Mfangano Island sites were most similar
to dry seasonal forests and also had more
open conditions. This evidence may turn
out to be important in considering information about whether the diets of these
different species of Proconsul were similar
and in interpreting the effects of seasonality
on developing tooth tissues among different
species of Proconsul (Macho et al., 1996).
The paleosols also provide useful environmental information. Retallack et al. (1995)
have associated Proconsul from Rusinga
Island with soils interpreted as having supported riparian woodland early in the ecological succession of streamsides. These
workers found no evidence of soils that
would indicate extensive dry grasslands or
wet rain forest. Substantial paleobotanical
remains are found on Rusinga and
Mfangano. The type of P. heseloni was
deposited by a predator in a large hollow
tree (Walker & Teaford, 1988). Fossilized
fruits have been found in the same paleosol
as the partial skeletons, some teeth of which
form the biggest sample for this study, at the
Kaswanga Primate Site (Walker et al., 1985)
and again these paleobotanical finds point to
potential differences in seasonality and diet
in Proconsul from Rusinga Island.
On the basis of histological sections of
nine molar teeth attributed to P. africanus,
P. major and P. nyanzae, Gantt (1983,
1986), has previously reported that linear
measurements of enamel indicate thick
enamel, relative to body size estimates.
Gantt estimated enamel thickness in these
  
species of Proconsul as equivalent to that in
Sivapithecus. However, Andrews & Martin
(1991) defined enamel thickness in a different way, using the dentine cap area to correct for body size, and found specimens of
both P. africanus and P. major from Songhor
and Koru to have thin enamel. These
results are consistent with a predominantly
frugivorous diet with limited degrees of
folivory, similar to extant forest-living,
arboreal cercopithecine monkeys. Nothing
further has been published about enamel
thickness or about enamel and dentine
microstructure in P. heseloni or P. nyanzae
which might contribute to our understanding of the variation in enamel thickness
between these species or indeed on the
underlying processes of enamel growth in
these early Miocene hominoids.
Kelley (1992, 1993, 1997) has proposed
that one way of distinguishing between Old
World monkeys and apes would be to define
their life history profiles more precisely and
that it would be important to learn more
about life history profiles in early Miocene
hominoids. Smith (1989, 1991, 1994) and
Smith et al. (1995) have demonstrated that
many life history traits correlate with age of
first permanent molar emergence or brain
weight, for example. Kelley (1997) has
drawn on the apparently tight relationship
between brain weight and M1 emergence
(but see Smith et al., 1995) and used cranial
capacity estimates available for P. heseloni to
suggest that an approximate age of emergence for M1 in this taxon would have
been 20·6 months. Kelley has cautiously
argued that this result may point to a more
prolonged set of life history traits in P.
heseloni than would be expected for an
early Miocene catarrhine of the same body
size.
A key aim of the present study is to
reconstruct the sequence and timing of
dental development in P. heseloni using a
variety of techniques. It is clear that there
is much to learn about growth and devel-
165
PROCONSUL
opment and about life history in Proconsul.
Thus, the present study attempts to establish a preliminary chronological schedule for
dental development in Proconsul heseloni.
There are now several juvenile partial skeletons associated with developing tooth
germs from Rusinga Island. Some idea
about a schedule of dental development in
this one species of Proconsul would make it
easier to associate these germs securely as
different individuals. A time scale for dental
development would also provide a better
comparative framework to describe juvenile
postcranial material. A second aim of this
study is to report further on enamel thickness in P. heseloni and P. nyanzae and on the
processes through which enamel grows
thicker or thinner. Thirdly, we aim to
describe microanatomical features in the
enamel and dentine of Proconsul that can be
compared to other species of both extant
and Miocene monkeys and hominoids.
Describing growth processes that underlie
morphological characters in both enamel
and dentine between different species of
primate is a sound way to establish developmental homologies which are useful for
phylogenetic analyses.
Materials
This study combines information from
ground sections of Proconsul teeth with data
from perikymata counts made from surface
replicas of other teeth. Four developing
mandibular permanent tooth germs (I1, I2,
M1 and M2) and two deciduous mandibular
teeth (dm1 and dm2), attributed to P.
heseloni (Figure 1) were prepared for histological examination (Individual IV from the
Kaswanga primate site on Rusinga Island).
These teeth had well-preserved, unworn
incisal or occlusal enamel, although in
some of the germs the lateral enamel was
incomplete or abraded post-mortem at the
developing cervix. It should be noted that at
least ten partial Proconsul skeletons were
166
. . 
ET AL.
Figure 1. P. heseloni teeth belonging to the juvenile specimen prior to sectioning. (All to the same scale
with a mm scale bar at the foot of the plate.) Top row left to right: dm1 buccal view, dm2 lingual view, M1
occlusal view. Middle row left to right: dm1 occlusal view, dm2 occlusal view, M1, fractured base of crown.
Bottom row left to right: I2 germ, I1 germ, M2 germ occlusal view.
comingled at the Kaswanga Primate Site. In
nearly all cases, the maxillary and mandibular bone had been broken up so that isolated teeth were collected from the deflation
surface. Teeth were matched to individuals
by size, degree of wear and interstitial facets,
but this is a difficult undertaking and there
may have been mistaken allocations. Five
mandibular permanent teeth attributed to
a single adult specimen of P. heseloni
  
PROCONSUL
167
Figure 2. P. heseloni teeth belonging to the adult specimen prior to sectioning. (All to the same scale with
a mm scale bar at the foot of the plate.) Top row left to right: canine, M1 occlusal view, M1 mesiobuccal
view. Middle row: base and incomplete lingual aspect of canine. Bottom row: occlusal views of P3, M2 and
M3.
(Individual III from the Kaswanga Primate
Site on Rusinga Island) were also prepared
for histological examination (Figure 2).
These were a canine, P4, M1, M2 and M3
from the lower right mandibular quadrant.
Although worn occlusally, each of these
teeth preserves the lateral enamel on one or
more aspects of the crown. In addition, two
complete adult tooth crowns without roots
preserved (KNM-RU 1721 and KNM-RU
1695, both surface finds) attributed to P.
nyanzae were also prepared for histological
examination (Figure 3). These are an M1
and a right M2 respectively. All of these
teeth are housed in The Kenya National
Museum, Nairobi. In addition all teeth
attributed to Proconsul and housed in The
Kenya National Museum, Nairobi were
examined and many included as part of this
study.
Other ground sections of primate teeth
including Pan troglodytes, Gorilla gorilla,
Pongo pygmaeus, Hylobates moloch, Hylobates
(Symphalangus) syndactylus, Theropithecus
168
. . 
ET AL.
Figure 3. P. nyanzae M1 (RU 1721) and M2 (RU 1695) crowns prior to sectioning. (All to the same scale
with a mm scale bar at the foot of the plate.) The three views on the left hand side are of RU 1695 and
the three views on the right hand side are of RU 1721.
gelada, and Cebus apella were also used for
reference in this study. These sections form
part of a large reference collection housed in
the Department of Oral Biology, The
Dental School, University of Newcastle
upon Tyne. Many are from zoo animals
(the great apes) but others are of unknown
provenance.
Methods
Perikymata
All teeth housed in the National Museum
of Kenya, Nairobi, that are attributed to
Proconsul were first examined using a
Wild M8 binocular microscope. Those
that preserve surface incremental markings
  
(perikymata) over some or all of their buccal or lingual enamel were cleaned with
alcohol and cotton wool and impressions
taken of the buccal and or lingual surfaces
using the Coltene President putty Light
Body wash system (Beynon, 1987). The
moulds were then cast in Spurr Resin following the methods described by Beynon
(1987). The resin replicas were sputter
coated with gold to maximize surface
reflectance. Counts of perikymata were
then made with the replica illuminated in
polarized incident light using a Wild M8
binocular microscope at appropriate magnifications for each tooth. These magnifications ranged between 20 and 80 times.
All counts were made with the tooth surface mounted perpendicular to the optical
axis of the microscope and with the tooth
continually tilted on a microscope stage to
maintain this relationship. Counts were
recorded as numbers of perikymata present
per millimetre of the total tooth height
along the buccal or lingual surfaces.
Approximately 45 counts of perikymata on
various aspects of 25 teeth were made. The
counts were tabulated from the most occlusal or incisive part of the tooth to the
cervix. Rarely was it possible to make complete counts of perikymata on a tooth.
Where areas of tooth were abraded or
worn, estimates of the numbers of missing
perikymata within any one millimetre of
the tooth surface under study were made
(i) on the basis of true counts made adjacent to these regions, or alternatively (ii)
on the basis of actual counts made in
contralateral teeth from the same specimen. In practice, the trends in packing
patterns were obvious and facilitated reconstruction of sequential counts estimated as
above. In this way a general profile of
perikymata counts and of their packing
patterns was recorded for most tooth types
of Proconsul. Any portion of any count that
was estimated appears in brackets in
Appendix 1.
PROCONSUL
169
Histological methods
Each of the teeth to be sectioned was first
cleaned under a dissecting microscope using
dental instruments, alcohol, and cotton
wool. The teeth were then photographed
(Figures 1, 2, 3) and replicated using the
Coltene President putty and Coltene Light
Body wash silicone addition curing impression system (Beynon, 1987). Teeth were
then dehydrated in alcohol and acetone and
included in Clear Cast Resin. In the case
of the dm1, dm2, I1, I2, M1 and M2 of the
juvenile specimen, just one section was cut
buccolingually through the tooth using
an annular diamond saw. Each of these
sections was made either centrally through
the incisal edge of incisors or, in the case of
the other teeth, mesially through the tallest
buccal cusp and lingual cusp. In the case of
the permanent molar teeth of the adult
specimens, one section was cut buccolingually through the mesial cusps and another
through the distal cusps with the aim of
preserving the points of both dentine horns
in each section. All sections were then
lapped plane parallel with a PM2 Logitech
lapping jig to a thickness of approximately
100 ìm (range 99 to 155 ìm for all the
sections cut) such that the point of the
dentine horn was preserved within the section as truly axial as possible to the plane of
section through the cusps. Figure 4 illustrates in outline one section from each of the
teeth used in this study. The remaining cut
block faces of each tooth were then removed
from the Clear Cast resin and replaced in
the Coltene moulds in their correct positions. Composite resin light-curing restorative filling materials, previously colour
matched to each tooth, were then placed
into the moulds between the cut block
faces to restore the teeth to their original
dimensions and appearance. Light curing
was done sequentially in layers of appropriate colour in the manner prescribed to
restore their original appearance. In this
way, a total of 18 ground sections were
170
. . 
ET AL.
Figure 4. Crown outlines, drawn from ground sections, of the teeth used in the histological part of this
study. One section only from each tooth is represented even though several posterior teeth were sectioned
more than once (see text). From top left to right through rows 1 and 2: dm1, dm2, I1, I2, M1, M2 (juvenile
P. heseloni) and M1. Row 3: canine P4, M3 (adult Proconsul heseloni). Bottom row: M1 and M2 (P.
nyanzae). Four tooth sections were reconstructed over the cusps in order to estimate enamel cap area and
EDJ length used for the calculations of relative enamel thickness. (None of the linear enamel thickness
measurements that appear in Table 1 were made on reconstructed outlines.) Representations of the high
power reconstructions are shown with dashed lines as appropriate.
  
prepared from 13 teeth. Ground sections
were first examined in polarized transmitted
light, then in reflectance mode with a Leica
laser confocal microscope at key locations.
Measurements in this study were made both
from high power photomontages of the
tooth sections and also directly using a Zeiss
Filar micrometer eyepiece.
Enamel thickness
For several unworn anterior and posterior
teeth, of both P. heseloni and P. nyanzae, it
was possible to make linear measurements
of enamel thickness. For some other teeth,
as in previous studies on enamel thickness,
minor reconstructions on tracings of crown
outlines were possible, either at the cervix
or at the cusp tips to correct for damage
or wear. It was then possible to make
additional estimates of the area of the
enamel cap, the dentine cap and the length
of the EDJ in four slightly worn or damaged
teeth. Measurements of enamel thickness
were made in several ways that reflect previous studies on enamel thickness and which
therefore allow comparison with the results
of these studies. Linear measurements of
enamel thickness were made on teeth where
there was no occlusal wear, in the way
detailed by Beynon & Wood (1986) and in
Figure 1 of Macho & Berner (1994), but
were made here on both mandibular and
one maxillary tooth. Measurements 1 and 8
were omitted as they are not directly comparable in upper and lower teeth. Andrews
& Martin (1991) present data for enamel
thickness in P. africanus and P. major. Two
measurements of enamel thickness as
defined by Martin (1983) were therefore
included to facilitate comparisons that are
derived from measurements of the enamel
and dentine cap area and from the length of
the enamel dentine junction. These were:
average enamel thickness (the area of the
enamel cap ‘‘c’’ divided by the length of the
enamel–dentine junction ‘‘e’’ as measured
from longitudinal sections of teeth) and
PROCONSUL
171
relative enamel thickness (the average
enamel thickness value, c/e, corrected as a
dimensionless index relative to ‘‘b’’, the area
of the dentine cap).
Enamel cross striations and striae of Retzius
Evidence supporting the fact that enamel
cross striations represent circadian increments of growth has been reviewed previously (Bromage, 1991; Dean, 1987, 1989,
1995a). Counts of cross striations can be
used to estimate the time of cuspal enamel
formation. Measurements of the distance
(spacing) between cross striations provide
an estimate of the daily rate of enamel
secretion. It is also well established that
counts of regular striae of Retzius in enamel
or of surface perikymata can be used to
calculate the time of lateral enamel formation when the number of cross striations,
or days, between them is known (Bromage
& Dean, 1985; Dean, 1987; Beynon & Dean
1998). In many places in the sections of the
permanent teeth of P. heseloni and P. nyanzae it was possible to see enamel cross
striations and regular striae of Retzius. However, these were less clear in the ground
sections of the deciduous teeth. In the cuspal enamel of the P. nyanzae M2, enamel
cross striations were exceptionally well preserved and could be tracked continuously
from the dentine horn to the outer surface of
the enamel along paths of groups of prism.
This tooth was therefore chosen to make a
more careful comparative study of cross
striations in cuspal enamel in Proconsul and
other primates. Figures 5(a) and 5(b) are
confocal reflected light images of cross
striations at the EDJ and at the surface of the
cuspal enamel in the M2 of P. nyanzae.
Cuspal cross striations
Measurements of cross striations were made
in zones, or bands, of enamel spaced
approximately 30 days apart (e.g., at roughly
monthly intervals) through the cuspal
enamel of the mesiobuccal cusp of second
  
molars of P. nyanzae, H. sapiens, Pan
troglodytes, G. gorilla, Pongo pygmaeus, H.
moloch and T. gelada. Data for a modern
human dm2 are also included. These data
are presented as graphs for each taxon. Each
box plot in each graph is equivalent to a
monthly zone and represents between 50
and 100 measurements of the distance
between cross striations within that zone,
depending on how many could be reliably
measured. The median values of the
measurements of cross striations for each
monthly zone in KNM-RU 1695 were used
to calculate median values for inner, middle
and cuspal enamel. The enamel prism track
used in the mesiobuccal cuspal enamel was
divided into three equal linear portions
between the dentine horn and the cusp tip.
Zones one to four were contained in the
inner portion, zones five to eight in the
middle and zones nine to 11 in the outer
portion. Other measurements of cuspal
cross striations in the Proconsul sample were
compared with these and found to match
well. Therefore, an overall average cuspal
enamel secretion rate was calculated in
order to estimate the time taken to form
known thicknesses of enamel in other
unworn Proconsul teeth. The times for cuspal
enamel estimated in this way for several
teeth were subsequently used in one of the
methods for calculating crown formation
times in unworn teeth (see below).
Form and periodicity of striae of Retzius
Measurements of the spacings between
adjacent striae in inner, middle and outer
enamel and of the angle of the striae of
Retzius to the enamel dentine junction
were made in as many of the Proconsul
ground sections as possible. These data were
collected in the same way as in previous
studies of great ape enamel (Beynon & Reid,
PROCONSUL
173
1995). Total counts of the striae of Retzius
were made in as many of the Proconsul
ground sections as possible. Counts were
made between the estimated position of the
first striae that appeared at the surface of the
enamel (as a perikyma) to the last stria
formed at the enamel cervix. This portion of
the enamel is referred to as the lateral
enamel in this study (but is equivalent to
that defined as the imbricational enamel of
some previous studies). The number of
days between adjacent striae of Retzius was
determined in one of two ways. Direct
counts of cross striations between Retzius
lines were possible in some sections on
photomontages. In other places two authors
independently measured the average distance between cross striations and striae of
Retzius in the same field of view. The
average number of days between striae was
estimated in this way. The total number of
striae in the lateral enamel of a tooth multiplied by the number of days between two
adjacent striae is equivalent to the total
lateral enamel formation time.
Incremental markings in dentine
While cross striations in enamel are better
described in primates than daily (von
Ebner’s) lines are in dentine, the experimental evidence for these lines being daily in
primates and in other animals is probably
better than that for enamel cross striations
(see Dean et al., 1993a; Dean, 1995a;
Ohtsuka & Shinoda, 1995; and Erickson,
1996 for reviews). Long-period incremental
markings (Andresen lines) that match the
periodicity of striae of Retzius in enamel,
also exist in dentine (Dean, 1995a). Both
long-period and daily lines are preserved in
many of the sections of Proconsul and the
spacings of both were measured. Measurements of the spacing between these lines
Figure 5. (a) Confocal reflected (backscattered) light image of enamel cross striations at the EDJ in P.
nyanzae. (b) Confocal reflected (backscattered) light image of enamel cross striations at the outer enamel
surface in P. nyanzae. (Fieldwidth 220 ìm in both micrographs.)
174
. . 
were made in the cuspal regions of teeth and
close to the enamel–dentine junction.
The following eight criteria were carefully
considered when identifying daily lines in
extant primate material and in Proconsul
dentine: (i) markings in dentine should
show a calcospheritic pattern (Boyde &
Jones, 1983) close to the granular layer of
Tomes in the root and gradually become
more laminar in their contour, (ii) they
should appear as a continuous series of
evenly spaced lines, (iii) they should follow
the contours of the growing tooth crown and
root, (iv) they should be maximally spaced
in the axial plane of the tallest cusp, (v) the
spacing between daily lines in dentine close
to the enamel–dentine junction should
match that predicted from the geometry of
the enamel forming at the same time, (vi)
the number of short-period daily increments
in enamel and dentine growing at the same
time (between accentuated markings that
occur in both enamel and dentine) should
be equal in number, (vii) when visible, the
number of daily lines between long-period
markings in dentine should be the same as
that for cross striations counted between
adjacent striae of Retzius in the same individual (Dean, 1995a), (viii) the spacing of
dentine increments in a given part of the
tooth crown or root should be equal to or
close to values for the rate of dentine formation determined in experimental studies
of humans and nonhuman primates. Figure
6 illustrates daily lines in Proconsul dentine.
The mean value for the spacings of incremental lines in dentine was used to calculate
the average daily rate of dentine formation
in the Proconsul teeth as follows. A line
equivalent to the last formed stria of Retzius,
and therefore formed at the same time as
enamel completion, was traced into the dentine from the enamel cervix up to the axial
plane of the tallest cusp with the longest
enamel formation time on each ground section. The distance between the dentine horn
and the point at which this line crossed the
ET AL.
axial plane of the cusp was measured. The
total length of the line (in microns)
measured along the path of dentine tubules
was divided by the mean value of the incremental lines (in microns). This method of
calculating crown formation using dentine is
described in more detail in Dean (1998).
The spacing between daily lines in dentine
were also measured close to the enamel–
dentine junction and used to calculate the
ratio of dentine to enamel formation in
Proconsul. In addition, daily lines in the
dentine of H. moloch, H. (Symphalangus)
syndactylus, were measured for comparison
with the results obtained for Proconsul.
Estimates of crown formation times
Estimating the total time to form enamel
from histological sections is complicated.
Different molar and premolar cusps differ in
cuspal enamel thickness and striae counts on
the lingual and buccal aspects of molar tooth
sections also often differ. There is some
relationship between the two variables since
thicker cuspal enamel is associated with
fewer striae in lateral enamel and conversely,
thinner cuspal enamel with a greater
number in the same tooth when enamel
formation begins and ends in both cusps
together (Ramirez Rozzi, 1993, 1995). If
cusps were to begin to mineralize together,
and if the buccal and lingual cervix were
coincident, such that enamel formation ends
at the same time on all aspects of the tooth,
the sum of cuspal enamel formation times
and lateral enamel formation times would be
equal on both lingual and buccal aspects of
the same tooth. However, if as there is,
disparity between the initial times of cusp
mineralization and/or a cervical enamel
margin that continues to form for longer on
the buccal or lingual aspect, then estimates
of total enamel formation times will differ
when made on different aspects of the same
tooth.
In incisors, canines and premolars, estimating the total crown formation period
  
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175
Figure 6. Daily lines in dentine in (a) the midline axial plane of the cusp of a juvenile M1 of P. heseloni
and (b) daily lines in the cervical dentine of the adult permanent M1. (Transmitted light. Original
magnification 500. Fieldwidth 120 ìm in both micrographs.)
using cuspal enamel formation times and the
total buccal stria or perikymata counts was
straightforward in both species of Proconsul.
One method of estimating total enamel formation times in molars of P. heseloni in
unworn tooth sections was by summing the
estimate for mesiobuccal cusp formation
time with that for lateral enamel formation
time estimated from the same mesiobuccal
aspect. In order to be objective and consistent on all occasions the mesiobuccal cusp of
P. heseloni molars, which contains the first
formed enamel, was used and the number
of additional striae in the lateral enamel of
that same cusp to the end of enamel formation was counted. A second method of
estimating crown formation times was by
using incremental markings in dentine when
possible as described above. A third method
of estimating crown formation times in P.
heseloni was to combine the histological estimates for the cuspal enamel formation times
176
. . 
(mesiobuccal cuspal times in molars) with
average perikymata counts made on the
buccal (incisors, canines and premolars) or
mesiobuccal (molars) cusps. In this way
estimates for canines and P3s, for example,
could be included, and a more realistic estimate of the average lateral enamel formation
time for several teeth of each tooth type used
in the composite reconstruction. In the two
more complete sections of P. nyanzae it was
possible to estimate enamel formation times
in more than one cusp. It was also possible
to use daily lines in dentine to estimate
crown formation times for each tooth. These
data are presented in full together with those
for P. heseloni.
Root extension rates
Three things must be measured in order to
estimate the rate at which the crowns and
roots of teeth grow in length. (i) The daily
rate at which cells produce matrix. (ii) The
direction of cell movement and (iii) the
number of mature secretory cells active at
any one time (their rate of differentiation).
Shellis (1984) has expressed the ‘‘extension
rate’’ of teeth at the enamel–dentine junction in the crown or at the cement–dentine
junction (CEJ) in the root mathematically.
In the equation c=d{sin I/tan D)cos I},
‘‘c’’ is the extension rate, ‘‘d’’ the daily rate
of dentine secretion, Angle ‘‘I’’ is the angle
the dentine tubules make with the root surface and Angle ‘‘D’’ is the angle between an
incremental or accentuated line and the root
surface. These variables are illustrated with
respect to the root dentine of the P. heseloni
P4 in Figure 7. The equation defines how
each of these variables can be used to estimate the rate of tooth root extension. In
order to calculate the rate of extension of
tooth roots in Proconsul, three things need to
be measured from photomontages made
using high power reflected or transmitted
light images of tooth roots. These are: (i)
The amount of tissue secreted in a day
which is equivalent to the spacing between
ET AL.
daily lines in dentine, (ii) the direction of
travel of the odontoblast relative to the EDJ
or CEJ (which can be inferred from the
alignment of a dentine tubule) and (iii) the
angle that the active cell sheet subtends to
the EDJ (which is a reflection of the number
of active secretory cells). It was possible to
measure each of these variables in the dm2
of the juvenile specimen and in the M1, M2
and P4 of the adult Proconsul specimen.
Estimates of the rate at which roots
extended (the extension rate) were therefore
possible in these teeth, in more than one
position in some teeth.
Sequence of dental development
In order to reconstruct a chronology of
dental development in P. heseloni, the positions of homologous accentuated lines in
each individual (that represent a single
event) were identified in ground sections of
both the adult and juvenile specimens. This
allowed the parts of teeth forming at the
same time in each individual to be crossmatched. To provide additional evidence for
a sequence of dental development in P.
heseloni, linear hypoplastic markings, visible
on the resin replicas of all of the permanent
upper and lower teeth of the exquisitelypreserved specimen KNM-RU 7290 were
studied across all teeth. On the basis of the
combined evidence from accentuated lines
in the ground sections and from the distribution of linear hypoplasia in KNM-RU
7290, a sequence of tooth development was
proposed. Details of the histological procedure for doing this in the ground sections
are detailed here.
Examination of the dm2, M1, I1 and I2
germs of the juvenile specimen revealed neonatal lines in the dm2 and M1 that allowed
their dental development to be registered to
birth. An additional accentuated marking,
with a constant number of cross striations
between it and the neonatal line in the M1,
I1 and I2 also allowed these teeth to be
securely registered with each other. Since
  
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177
Figure 7. Incremental markings in the cervical dentine of the P. heseloni P4 (polarized light). Over these,
the tubule direction (Angle I) is indicated, the angulation of the incremental lines to the EDJ (Angle D)
and the distance c–c’ over which the extension rate is calculated using the formula ‘‘c=d[(sin I/tan D)–cos
I]’’ (Shellis, 1984) described in the text.
the last dentine formation occurred at death,
estimates of the length of time for dentine
to form in these tooth germs subsequent
to the occurrence of the accentuated line
made it possible to check that all germs
were compatible as belonging to one
individual.
Within the enamel of the M1, P4 and M2
of the adult specimen there were also several
irregular accentuated markings. The time
between each of these accentuated markings
was estimated in these teeth using cross
striations and striae of Retzius such that a
matching chronological sequence of lines
could be identified across the developing
dentition. In this way a precise sequence of
tooth mineralization was established for
these tooth types.
Estimates of the average cuspal enamel
formation times, the lateral enamel formation times for each tooth type and where
possible, estimates of the times of root
. . 
178
growth (derived from the formula to estimate extension rates as defined by Shellis,
1984) were then used to construct a composite chart of dental development in P.
heseloni. This summary of dental development is derived from different teeth belonging to different individuals and does not
therefore, represent a single individual.
Results and analysis
Enamel thickness
Sections of the incisor tooth germs attributed to P. heseloni (Individual IV) preserve
all of the cuspal enamel. Unlike exant Old
World monkey teeth where the lingual
enamel is either very thin (17–21% of the
buccal enamel thickness) or completely
absent (Shellis & Hiiemae, 1986), the
lingual enamel in Proconsul is thicker (63%
in I1 and 52% in I2 of the buccal enamel
thickness, see Figure 4) and resembles
that of New World monkeys and hominoids
in its thickness relative to the buccal
enamel. Gillings & Buonocore (1961) and
Shillingburg & Grace (1973) have presented
data for enamel thickness in human anterior
teeth, and report that like great apes, the
lingual incisor enamel is about two thirds
that of the buccal enamel thickness. In this
respect Proconsul resembles the majority of
extant New World monkeys and nonhuman hominoids more closely than extant
Old World monkeys.
Table 1 contains the data on enamel
thickness collected for eight teeth attributed
to Proconsul in this study. Compared to data
available for great apes and for P. africanus
and P. major (Andrews & Martin, 1991) the
two species from Rusinga Island reported
here have thicker enamel. Only the deciduous second molar falls into the thin category
as defined by the index of relative enamel
thickness. All of the permanent molars of P.
heseloni fall into the intermediate thick or
thick categories as defined by Martin (1985)
and Andrews & Martin (1991). Judged in
ET AL.
this way, the molar teeth of P. nyanzae
described here are certainly thicker and one
of them, the first permanent molar, even
approaches the ‘‘thick-hyperthick’’ category
as defined by Grine & Martin (1988).
Cuspal cross striations
The data derived from the section of M2
(KNM-RU 1695) are presented in Figure 9.
The mean cross striation repeat intervals for
each equal third of enamel thickness was
calculated as 4·4 ìm, 4·8 ìm and 5·4 ìm
respectively and an overall average value
(4·9 ìm) of these three means used as the
cuspal mean. Cuspal enamel thickness was
measured as 1600 ìm in this cusp, along
the prism direction, which when divided by
4·9 ìm equals 326 days of enamel formation. This is close to the same time as
estimated for this tooth cusp by counting
cross striations directly on the photomontage (two tracks from two different
montages in the same cusp were counted as
310 and 325 days). Measurements of occlusal enamel thickness along the prisms in the
cusps were then made in as many of the
sections of unworn Proconsul teeth as possible. These measurements and the cuspal
enamel formation times calculated from
them appear in Table 2. (Note that these
non-linear measurements along prism paths
are slightly different from the direct linear
measurements of cuspal enamel thickness
that appear in Table 1 as defined by Macho
& Berner, 1993.)
Measurements of the cross striations are
presented in Figures 8, 9 and 10. The
mechanisms by which cuspal enamel grows
thick or thin appears to vary among the
primates surveyed here (albeit so far for one
tooth type only). Figure 8 shows that in
H. moloch, Gorilla, Theropithecus and the
human dm2 there is a gradient from slower
inner rates to faster rates nearer the enamel
surface. The box plot for enamel at the
surface in H. moloch stands out as being the
only individual where enamel formation in
14·4
17·0
21·2
0·62
0·81
0·99
1·44
1·19
1·25
RM1
RM1
RM2
RM2
27·6
22·4
22·3
13·4
0·65
LR P4
LR M1
LR M1
LR M2
LR M2
LR M3
LR M3
10·5
16·4
19·1–24·4
0·36
0·68
0·98
LR dm2
LR M1
LR M2
Tooth
type
Average
enamel
thickness
(c/e)
1·58
1·76
1·57
1·5
1·34
1·11
Linear
enamel
thickness
measurement
No. 3
(mm)
1·65
1·61
1·17
0·89
0·82
0·88
1·18
Linear
enamel
Relative
thickness
enamel
measurement
thickness
No. 2
{(c/e)/sb}100
(mm)
1·56
1·52
1·76
0·88
0·87
1·3
Linear
enamel
thickness
measurement
No. 4
(mm)
1·44
1·74
0·93
0·88
0·84
0·9
1·3
Linear
enamel
thickness
measurement
No. 5
(mm)
1·17
1·61
0·64
1·04
Linear
enamel
thickness
measurement
No. 6
(mm)
1·32
1·60
0·87
0·64
0·94
Linear
enamel
thickness
measurement
No. 7
(mm)
The index number of each ground section appears in column 1 split by taxon and by juvenile and adult specimens. Enamel thickness data are presented for
posterior teeth of P. heseloni and P. nyanzae. Average enamel thickness and relative enamel thickness measurements are as defined by Martin (1983) and described
in the text. Linear enamel thickness measurements 2 and 7 are as defined by Macho & Berner (1993) but were made on both upper and lower teeth here.
(Measurements 1 and 8 were not made since the presence of cingula complicates these lateral linear measurements of enamel thickness when data for upper and
lower teeth are compared.)
Juvenile
P. heseloni
HT3/91E
HT3/91F m
HT3/92G m
Adult
P. heseloni
HT2/91B
HT2/91C m
HT2/91C d
HT2/91D m
HT2/91D d
HT2/91E m
HT2/91E d
Adult
P. nyanzae
RU 1721 m
RU 1721 d
RU 1695 m
RU 1695 d
Index number of
each section
(m=mesial;
d=distal)
Table 1
  
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179
286
286
1400
1400
1570
1600
1600
1717
URM1
URM1
LRM2
LRM2
320
327
327
350
153
153
163
163
(184)
159
184
780
900
750
750
800
800
(900)
82
122
400
600
Cuspal
formation time
(=occl. enam. thick/4·9 ìm)
(days)
LR C
LR P4
LR M1
LR M1
LR M2
LR M2
LR M3
LR M3
LR I1
LR I2
LR dm1
LR dm2
LR M1
LR M2
Tooth
type
Occlusal
enamel
thickness
along prisms
(microns)
63
80
87
66+
70+
77
65+
82
24+
Total
striae
counts
(Lingual)
69
56
72
96
61+
142+
109
54+
51+
66+
22+
40+
35+
Total
striae
counts
(Buccal)
414
336
432
378–576
710
400–545
435–270
255–330
330–350
385
305–325
410
120
200
175
Range of
lateral enamel
form. time
estimates
(days)
734
663
759
728–926
591–611
696
863
553–698
433–598
418–493
514–534
304
282
297
Range of
total crown
formation
estimates
(days)
2·0 (mb)
1·8 (db)
2·1 (mb)
2·0 (dl)–2·5 (db)
1·6 (mb)
1·2 (mb)
1·4 (mb)
2·4+ (b)
1·9 (b)
0·8+ (mb)
0·77+ (b)
0·81+ (b)
Crown formation
time (cusp+lat.).
The lateral aspect
or cusp used is
shown in parentheses
(years)
. . 
The index number of each ground section of each Proconsul tooth appears in column 1. Sections through the mesial or distal cusps of molars are indicated (m
or d). Cuspal formation times were calculated by dividing occlusal enamel thickness by the mean cuspal daily rate, 4·9 ìm. Stria counts made on buccal (b) and
lingual (l) aspects of mesial and distal sections are shown and a range indicated when possible. Ranges of total crown formation times are indicated in column
8 but in the last column (9) molar crown formation times in P. heseloni are calculated using the mesiobuccal cusp only (mesiobuccal cuspal enamel
formation+mesiobuccal lateral enamel formation) since this cusp forms first in molar teeth. In one worn M2 section (HT2/91D dist.) no cuspal enamel formation
time could be estimated and values for M2 were used for the unworn M2 section HT3/91G and are bracketed in columns 3 and 4. Molar crown formation times
in P. nyanzae are calculated using all measures of cuspal enamel thickness possible in all cusps as well as all corresponding stria counts on all aspects of the sections
available.
Juvenile
P. heseloni
HT3/91A
HT3/91B
HT3/91D
HT3/91E m
HT3/91F m
HT3/91G m
Adult
P. heseloni
HT2/91A
HT2/91B
HT2/91C m
HT2/91C d
HT2/91D m
HT2/91D d
HT2/91E m
HT2/91E d
Adult
P. nyanzae
RU 1721 m
RU 1721 d
RU 1695 m
RU 1695 d
Index No. of
tooth section
m=mesial;
d=distal
Table 2
180
ET AL.
  
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181
Figure 8. Plots of measurement of cuspal enamel cross striation spacings (ìm) in Hylobates moloch, Gorilla,
Theropithecus and a human dm2. The x axis is in monthly zones from the EDJ to the outer cuspal enamel.
In all cases measurements were of the cuspal enamel of M2 (or human dm2). Each box plot represents
between 50 and 100 measurements of cross striations. The median value is the horizontal line through the
box, the 25%ile and 75%ile respectively are represented by the upper and lower boundaries of the box and
the whiskers extend to the 10%ile and 90%ile. Outliers are plotted as open symbols. Cross striation repeat
intervals in each of these four plots rise from values around 3 or 4 ìm per day to higher values of between
5 or 6 ìm per day. Only in Hylobates moloch is there a slowing of the outer enamel layer.
182
. . 
Figure 9.
ET AL.
  
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183
Figure 9. Plots of enamel cross striation spacings in (a) Proconsul nyanzae, (b) Pan troglodytes and
(c) Homo sapiens. Early values remain near constant for several months in all of these plots. Those for
Proconsul are however, all at a higher rate than those in Homo and Pan. All axes are as in Figure 8.
the last surface zone slows down with
respect to the rest of the outer enamel.
Figure 9 shows that rates of enamel formation in Pan, Homo and Proconsul remain
at close to the same value for some months
into cuspal enamel formation. This pattern
of formation appears to be different from
that described in the thinner fast forming
cusps (Figure 8). The swift rise towards the
surface in the last few months of cuspal
enamel formation in Proconsul also appears
more similar to the pattern for modern
human or chimpanzee M2 cuspal enamel.
Figure 10 shows box plots for rates of
enamel formation in two molar tooth cusps
of Pongo (one mesiobuccal cusp of an M2
and one mesiobuccal cusp of an M3 from a
different individual). Rates of enamel formation are similar in both tooth cusps
but different again to the previous patterns
of cuspal enamel formation described in
Figures 8 and 9. In Pongo, rates of enamel
formation rise quite quickly but then level
off to values that are below those for other
primates shown in Figures 8 and 9. In this
respect Pongo and Proconsul are different.
The total number of approximate
monthly zones for each plot in Figures 8, 9
and 10 gives a good idea of how long the
cuspal enamel takes to form in these teeth.
Prisms weave around within the section and
can be followed easily in two dimensions in
the plane of the section. However, they also
more than likely weave in and out of the
plane of section to some degree in some
places. The degree to which they do this is
unknown, but it is likely that true cuspal
enamel formation times are close to the
values calculated here, as four different
methods of calculation give results to within
184
. . 
ET AL.
  
5–10% of the mean values for four methods
used (Dean, 1998). Thus in humans, M2
cuspal enamel in the second permanent
molar takes about 16 months to form
(Figure 9). By way of contrast, human M3
cuspal enamel can take in excess of two
years to form. In H. moloch (Figure 8) cuspal
enamel formation takes about five months
and in P. nyanzae about 11 months to form.
With respect to the absolute time it takes to
form cuspal enamel in these M2s, the time it
took for P. nyanzae (Figure 9) falls among
the values for living great apes and happens
to be the most similar to the Pan M2 used in
this study.
Both species of Proconsul appear to be
unique among those primate species
represented here in that median values for
the spacing between inner enamel cross
striations are in excess of 4 ìm at the
enamel–dentine junction (EDJ) and approach 7 ìm at the enamel surface. The
median values for all the other primates
studied (see Figures 8, 9 and 10) are less
than this in equivalent zones within the M2
cusps. While the best yet, this data on cross
striation spacings is still limited and while
there is additional data for extant hominoids
(Beynon et al., 1991) we do not yet know in
detail what patterns of enamel formation
rates occur other cusps and in other tooth
types.
The pattern of a high daily rate of enamel
formation at the EDJ and of an increase in
cross striation spacing in the outer monthly
zones is present in the cuspal regions of all
other tooth sections of P. nyanzae and P.
heseloni. A mean cuspal range of 4–6 ìm per
day was typical for Proconsul in this study.
Daily rates of enamel formation close to the
EDJ are similar along the whole length of
the EDJ in the crowns of all primates studied
PROCONSUL
185
so far (in this respect work in preparation
extends data presented in Beynon et al.,
1991). In lateral enamel and in enamel close
to the cervix in Proconsul, mean values for
measurements of cross striations at or close
to the EDJ fit with this finding and are about
4 ìm in all of the tooth sections where it was
possible to make measurements. Values
towards the enamel surface in lateral and
cervical enamel however, are lower than the
maximal values recorded in cuspal enamel.
This is reflected in the data presented below
for long-period striae spacings close to the
surface.
Stria morphology and periodicity
The comparative data for stria spacings and
angulation to the EDJ made on large numbers of M1s appear in Table 3. There is a
general trend to reduce the width between
adjacent long-period striae towards the cervix in the outer enamel of the crown. The
angulation of the striae of Retzius to the EDJ
is an important variable which has considerable influence on how the geometry of tooth
growth can be described. For a given daily
rate of enamel formation, small angles
indicate a fast extension rate and large
angles a slow extension rate (Shellis, 1984).
Measurements of stria angles to the EDJ in
the occlusal third, the lateral third and the
cervical third of the lateral enamel in a large
comparative sample of hominoid teeth and
in Proconsul are presented in Table 4. In the
cervical region particularly, stria angles are
high in Proconsul. Besides the angle of
striae to the EDJ, there is a strong
‘‘S-shaped’’ form to the buccal cervical
striae in some Proconsul teeth. Figure 11
illustrates this stria morphology in P. heseloni
and P. nyanzae enamel.
Figure 10. Plots for cross striation spacings in an M2 and an M3 of Pongo pygmaeus. In these two plots
cross striation spacings rise swiftly from 2 ìm or 3 ìm per day to values around 5 ìm per day. However,
for seven or eight months thereafter these rates remain more or less constant. All axes are as in Figures 9
and 10.
. . 
186
ET AL.
Table 3 Comparative data for stria angles and stria widths in M1 only
Taxon
Homo sapiens
Pan troglodytes
Pongo pygmaeus
Gorilla gorilla
Proconsul heseloni
Proconsul nyanzae
Homo sapiens
Pan troglodytes
Pongo pygmaeus
Gorilla gorilla
Proconsul heseloni
Proconsul nyanzae
n
Occlusal striae
angles at EDJ
Mean1 S.D.
Lateral striae
angles at EDL
Mean1 S.D.
Cervical striae
angles at EDJ
Mean1 S.D.
20
23
10
28
1/2
1
13·01·5
9·01·8**
9·03·7*
7·03·1**
12–28
16
27·02·6
26·06·0
30·07·1
23·06·8*
18–21
21–30
32·0 1·8
31·0 4·3
41·0 5·6**
31·010·7
28–45
65–70
Occlusal striae
widths at
surface
Mean1 S.D.
Lateral striae
widths at
surface
Mean1 S.D.
Cervical striae
widths at
surface
Mean1 S.D.
37·02·8
28·01·6**
54·03·2**
42·05·0**
46
28·03·2
27·02·1
47·07·7**
33·05·3**
32–41
28
21·0 3·5
20·0 2·7
30·0 4·7**
27·0 4·6**
26
25
20
21
10
28
1/2
1
Significance with respect to Homo; *P<0·01, **P<0·001.
Comparative data for striae angles and striae spacings in first permanent molar teeth only for extant hominoids
(from Beynon & Reid, 1995) together with data for Proconsul M1 teeth only. (P values calculated using Student’s
t-test.)
In a few places it was possible to make
average measurements of both cross striations and regular striae of Retzius in the
same field of view. In the low lateral enamel
in RU 1695 average striae spacings were
30·8 ìm apart and average cross striation
spacings 5·25 ìm apart. Since 30·8/
5·25=5·9 this suggests a cross striation
repeat interval in this tooth, attributed to P.
nyanzae, of six days. Figure 12 is a confocal
micrograph of this region where it was
possible to count directly six cross striations
between regular long-period striae in this
region. In the lateral enamel of the central
incisor germ, attributed to P. heseloni, the
mean spacing between striae was 31·8 ìm
apart and mean cross striation spacings in
the same field of view 6·6 ìm apart. Since
31·8/6·6=4·8 this suggests a cross striation
repeat interval of five days. Independent
counts made directly and on photomontages in five different fields of view
consistently confirmed a five day repeat
interval in three P. heseloni teeth and a six
day repeat interval in the two P. nyanzae
teeth. Teeth from the same individual consistently have the same cross striation
repeat interval between regular striae of
Retzius (Dean & Beynon, 1991; Dean,
1995a). Since the P. heseloni teeth used to
measure and count the cross striation
repeat intervals belong to no more than
two individuals, and since both individuals
are represented in these counts, it follows
that all of the P. heseloni teeth used in this
study have a five day repeat interval
between regular striae of Retzius.
Rates of dentine formation
In the dentine of six out of the 11 histological sections of the P. heseloni teeth used in
this study, long-period lines were visible and
were measurable in the axial plane beneath
cusps (Table 4). In the developing I1 germ
  
PROCONSUL
187
Figure 11. ‘‘S-shaped’’ striae in the cervical enamel of the P. nyanzae M2 (left) and the P. heseloni M1
(right).
(Individual IV) they measured 25 ìm apart
maximally. In the high cusped M1 germ
(Individual IV) 16·7 ìm apart maximally,
and in other lower crowned premolars and
molars (Individual III) they measured on
average 12·5 ìm apart.
Given that there is a five day periodicity
between enamel striae in this individual, this
implies daily rates of dentine formation were
close to 5 ìm per day in the I1, 3·3 ìm per
day in the high cusped M1 and 2·5 ìm per
day in the other posterior teeth. Both in
these teeth and others, daily lines with this
expected periodicity in this position were
measured (Table 4). This enabled mean
daily rates of dentine formation in the cusps
of several teeth to be estimated specifically
for each tooth.
Two deciduous teeth, the dm1 and the
dm2 (Individual IV) had measurable daily
lines in the coronal dentine of around
3·5 ìm. Measurements made through the
whole thickness of the cuspal dentine in two
P. heseloni teeth (M2 and M3), demonstrated
that there was a constant rate of dentine
formation in the axis of cusps, as has been
demonstrated in apes and humans (Dean &
Scandrett, 1995). The mean value (n=23)
for spacings of daily lines made on the
photomontage of the M2 was 2·4 ìm
(S.D.=0·21, range=1·95–2·66). For the M3
(n=14) the mean value was 2·09 ìm
188
. . 
ET AL.
Figure 12. Confocal light image of striae of Retzius and enamel cross striations in the cervical region of the
P. nyanzae M2. There are six cross striations between adjacent striae. (Fieldwidth 360 ìm.)
(S.D.=0·31, range=1·66–2·83). No trend
in values from large to small, or vice versa,
existed through the cuspal dentine of these
teeth.
Measurements of spacings of daily lines in
the more lateral regions of the crowns of
both P. heseloni and P. nyanzae were much
smaller than those made in the axis of the
cuspal dentine (Table 4). At the EDJ they
were typically 1·5 ìm or less. Values around
2 ìm were more typical at the EDJ in occlusal areas between cusps and further in
towards the pulp chamber.
The ratio of the amount of dentine
formed to the amount of enamel formed
between the EDJ and accentuated lines
common to both tissues appear in Table 4.
This varied between 1:1·6 and 1:2·8 in P.
heseloni. The most extreme values occur in
the cervical region of the two molars attributed to P. nyanzae where ratios of 1:3 and
greater can be observed. By way of contrast,
in the dm2 (Individual IV) and the M1
(Individual III) attributed to P. heseloni, that
have clear neonatal lines which mark both
the enamel and dentine occlusally, the
ratio of dentine to enamel formation is 1:1
either side of the dentine horn. This occurs
here partly because the high rate of dentine
formation (3·5 ìm per day) closely matches
the rate of enamel formation (4·0 ìm per
day) in this position. However, some decussation in the enamel prisms here (but in
none of the dentine tubules) equalizes the
distance over which each tissue forms in this
time.
Crown completion times
The perikymata counts made from the
replicas of all Proconsul tooth surfaces are
presented in detail in Appendix 1 by tooth
type and by each aspect of each tooth
RM1
RM1
RM2
RM2
LR C
LR P4
LR M1
LR M1
LR M2
LR M2
LR M3
LR M3
LR I1
LR I2
LR dm1
LR dm2
LR M1
LR M2
Tooth
type
21
30
25
20
36
34
23
20
30
12
16
16
15
47
35
20
18
70
65
70
64
48
48
42
25
28
45
1:2·68
1:2·84
1:2
1:2·62
1:2 occ
1:1 occ
1:1 occ
1:1·59
22
21
35
12
14
24
19
28
1:1·98
1:1·84
45
Cv
30
35
Lat.
Dentine to
enamel ratios
at the EDJ or
occlusally (occ.)
if indicated
15
Occ.
Enamel stria
EDJ angles
(degrees)
10·3
12·2
12·5
16·7
15·0
25
Mean axial
long-period
dentine
lines
(microns)
2·75
2·75
2·1
2·5
2·5
3·0
2·5
5·0
5·0
3·5
3·5
3·3
2·4
Axial
1·8
1·5
1·7
2·0
1·8
1·3
2·5
Lat.
Mean daily
dentine lines
(microns)
1924
2146
2027
2259
1259
1174
1096
1531
1185
1706
1643
320
595
Lengths
from dentine
horn to cr.
completion
(microns)
1·9
2·1
2·0
2·25
1·7
1·6
1·2
1·7
1·35
0·94
0·90
0·25
0·46
Crown form.
times
estimated
using dentine
(years)
2·0
1·8
2·1
2·0–2·5
1·6
1·2
1·4
2·4+
1·9
0·8+
0·77+
0·81+
Crown form.
times using
enamel from
Table 2
(years)
PROCONSUL
In column 1 the index number of each ground section (mesial=m and distal=d) and tooth type appear for all Proconsul tooth sections. Stria angles are given
for occlusal, lateral and cervical thirds of the lateral enamel. Dentine to enamel ratios are also given. The mean values only for measurements of the spacing of
long-period and daily lines in dentine appear for the tallest cusp in each section. (For HT2/91/E mesial section n=14, mean=2·1, S.D.=0·31; for HT3/91G distal
section n=23, mean=2·4, S.D.=0·21.) The distance between the dentine horn in the tallest cusp of the section and a line corresponding to the end of enamel
formation in the dentine is given in microns (ìm). Crown formation times (in years) were calculated by dividing the length of this line by the mean daily rate for
the same cusp. The last column is reproduced from Table 2 to facilitate comparison of crown formation times using dentine and enamel.
Juvenile
P. heseloni
HT3/91A
HT3/91B
HT3/91D
HT3/91E
HT3/91F m
HT3/91G m
Adult
P. heseloni
HT2/91A
HT2/91B
HT2/91C m
HT2/91C d
HT2/91D m
HT2/91D d
HT2/91E m
HT2/91E d
Adult
P. nyanzae
RU 1721 m
RU 1721 d
RU 1695 m
RU 1695 d
Index No. of
tooth section
m=mesial;
d=distal
Table 4
  
189
190
. . 
ET AL.
Figure 13. The combined totals of cuspal enamel formation times estimated from the histological part of
the study and lateral enamel formation times estimated from perikymata counts from replicas (see in
Appendix 2). The inner vertical lines denote the cuspal enamel formation times. In this chart all
perikymata counts for each tooth type (both upper and lower) have been combined and the error bars
(1 S.D.) indicate the overall variation for lateral enamel formation only for each tooth type of P. heseloni.
surface. The total number of perikymata
on any tooth surface appears in the last but
one column. In general the perikymata
counts for P. nyanzae are slightly higher
than those for similar tooth types in P.
heseloni. The total perikymata counts for
anterior teeth presented here give a clearer
idea of the completed lateral enamel formation times in a large number of Proconsul
teeth and so complement the striae counts
made from the histological sections on the
buccal aspect. Table 2 contains data for
total striae counts on all aspects of all the
tooth sections prepared in the histological
part of the study. When data for upper and
lower teeth of the same tooth type are
combined the likely true extent of the contribution of the cuspal and lateral enamel
formation times to total crown formation
times of P. heseloni can be appreciated
(Figure 13).
Cuspal enamel formation times deduced
from the histological sections were used to
calculate crown formation times in three
ways (i) by summing cuspal and lateral
enamel formation times in the teeth where
complete crowns are represented in the
histological sections (Table 2) and (ii) by
summing cuspal formation times with data
for buccal or mesiobuccal perikymata
counts. The average crown formation times,
derived for this purpose from the perikymata
data for each tooth type, appear in the last
column of Appendix 2. A five day cross
striation repeat interval between perikymata
and striae of Retzius in lateral enamel has
been assumed for all P. heseloni specimens
and a six day interval for all the larger P.
nyanzae, and P. major specimens represented in this study. (iii) In five of the
juvenile and four of the adult specimens of
P. heseloni and in both molar teeth attributed
to P. nyanzae, it was possible to estimate
crown formation times using dentine. All
these estimates for crown formation times
appear in Table 4.
Root extension rates and the timing of root
formation
In four sections, the dm2 of the infant,
the M1, the P4 and the M2 of the adult
specimen, it was possible to make each of
  
Table 5
191
PROCONSUL
Proconsul root extension rate data
Tooth
dm2
M1 (apical 1/3)
M1 (apex)
P4 (cervix)
M2 (cervix)
M2 (apex)
Angle I
(degrees)
Angle D
(degrees)
Daily rate (d)
(ìm/day)
Extension rate
(ìm/day)
112
107
105
98
105
100
115
126
108
112
91
101
115
4·5
16
8
7
10
5·5
20
16
15
15
14
15
7
2·9
3·5
2·0
2·0
3·2
1·9
2·1
1·8
1·7
1·8
1·6
1·6
3·3
34·8
12·7
14·3
16·4
18·1
20·4
6·1
6·1
6·5
6·8
6·4
6·2
25·7
Data used to calculate root extension rates using the formula from Shellis (1984)
described in the text. All angular measurements and spacings between daily lines were
measured on montages constructed at 500 original magnification. The daily rates
that appear here are the mean values for as many measurements as possible in each
field of view under consideration and do not correspond to those given for different
regions in Table 4.
the measurements required to estimate
extension rates in the same fields of view.
Importantly, in the M2 and P4 it was possible to make these measurements in two
widely spaced positions in the root. Close to
the enamel cervix and also low in the apical
third of the root. The measurements and the
calculated extension rates appear in Table 5.
Extension rates in the cervical third of the
M2 and P4 were on average 6·5 ìm per day. In
the apical third of the root they were on average 14·5 ìm per day and close to the apex
21·5 ìm per day. The completed root lengths
for these teeth are not all known but are
approximately 7 mm in the P4 and 8 mm in
the M1 and M2. Given the state of preservation of these teeth and the fact that there is
cementum deposition apically, these root
lengths are only likely to approximate the true
lengths at apical closure. However, they do
allow some broad estimates of the time taken
to form roots. Root extension rate in the dm2
is estimated at 35 ìm per day. This is equivalent to 200 days for a tooth root of just under
6 mm long. Deciduous teeth contain incre-
mental lines with a constant angulation to the
root surface from cervix to apex implying a
constant extension rate. However, permanent
teeth in Proconsul begin to form roots slowly
and then speed up towards apical closure.
The times for root formation can therefore be
derived in different ways. If half the root
formed at the slower rate and half at the faster
rate, root formation would have taken around
2·4 years in the premolar and molar teeth. If
the middle third of the root is assumed to have
formed at an intermediate rate of 10·5 ìm per
day then the sum of the time for each third of
root formation is equal to 2·3 years.
Sequence of dental development
Figure 14 is a diagrammatic summary of
histological evidence for the sequence of
tooth development in P. heseloni. Table 6
is a summary of all the crown formation
times and root formation times calculated
using the different approaches adopted in
this study. In addition to these there are
three other lines of evidence that provide
information on the sequence of dental
. . 
Figure 14. The upper part of the Figure relates to the juvenile P. heseloni specimen. The line ‘‘Birth’’ runs through the neonatal lines in the M1 and dm2.
The lower line ‘‘Death’’ runs through the last dentine formed beneath the tallest cusp in I1, I2 and M2 (d). Accentuated lines in the I1 and I2 germs and
M1 germ allowed these teeth to be tied together developmentally. The times between birth and death in each of these teeth allow a timescale to be placed
on this sequence. The time of M2 crown formation exceeds that of the other germs and therefore cannot belong to the same specimen. The lower part
of the Figure relates to the adult P. heseloni individual. Crown completion in M1 is indicated by a dashed line. An accentuated line just above crown
completion and close to the cervix of the adult M1 corresponds with a line in the cusp of the M2 and is shown just above the dashed line in M2. The same
line can be seen in P4 just above the dotted line that indicated crown completion in M1. Another accentuated line in the cervix of the M2 (shown just
below the dashed line in M2) matches a line in the P4 cervix. The dashed line which represents adult M1 crown completion time was located in both the
M2 and P4 by counting the number of striae beyond the first accentuated line in each tooth. M3 cannot be sequenced with these teeth.
192
ET AL.
  
193
PROCONSUL
Table 6 Summary of crown completion times
Using perikymata
Using enamel
Using dentine
Tooth type P. nyanzae P. heseloni P. nyanzae P. heseloni P. nyanzae P. heseloni
dm1
dm2
I1
I2
C
P3
P4
M1
M2
M3
Maximum value of means
P. nyanzae
0·25
0·46
2·5
2·5
3·0–4·7
1·8
2·0
2·4
2·4
2·5
1·8
1·5
1·0
1·3
1·7
2·5
2·5
3·0–4·7
2·4
1·9
2·2
1·7
1·2
1·4
2·0
2·3
1·7
1·2
1·6
1·7
2·0
2·3
P. heseloni
0·25
0·46
2·4
2·4
2·5
1·8
1·7
1·2
1·4
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 P4 and second M2 of the adult P. heseloni
specimen and the same strong line in the
cervical enamel of the M1. 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 M1 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
M2s. 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 M2 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,
. . 
194
which are defined by Andrews & Martin
(1991) as having thin enamel. (iii) The daily
rates of cuspal enamel formation at the EDJ
in Proconsul were fast and in excess of 4 ìm
per day. (iv) The pattern of a prolonged
period of enamel formation in M2s at a near
constant rate in the inner cuspal enamel, but
then swiftly rising in enamel close to the
tooth surface, resembles modern human
and chimpanzee enamel formation. (v)
Daily cross striation repeat intervals between regular striae of Retzius, in P. heseloni,
fall into the range known for modern small
bodied monkeys and above the range known
so far for small gibbons and below the range
known so far for siamangs, baboons, great
apes and modern humans. The same repeat
interval in P. nyanzae falls between the
ranges documented so far for these primates. (vi) Both regular stria spacings, stria
angles to the EDJ and also occasionally, stria
morphology in the posterior teeth of Proconsul bear a close similarity to the condition in
Pongo. (vii) Daily cuspal and lateral rates of
dentine formation in Proconsul were slower
than those known for great apes and modern
humans but are close to those known so far
for small gibbons (H. moloch). (viii) The
ratio of dentine to enamel formed in lateral
and cervical regions of the crowns in Proconsul falls between 1:1·6 and 1:3 in posterior
teeth and is greatest in P. nyanzae. Values
approaching those in P. nyanzae have not so
far been documented in any other primate
teeth. (ix) The total period of dental development in P. heseloni appears to be between
6 and 7 years. (x) Crown formation time
estimates in M1 and M2 of P. nyanzae were
between 1·8 and 2·5 years.
Discussion
Enamel thickness
Enamel thickness has been an important
issue in studies of early Miocene hominoids
but studies of enamel thickness are fraught
by problems of how to measure it and how
ET AL.
to define it. Gantt (1983, 1986) made linear
measurements of cuspal enamel thickness in
a large number of primate teeth and plotted
these data against body weight for primates.
It emerged from this analysis that Proconsul
had thick enamel equivalent to that in
Sivapithecus from the late Miocene of South
Asia. However, at that time there were no
reliable body weight estimates for the various species of Proconsul and, in fact, Gantt
was only able to plot data for one out of nine
sections of the Proconsul teeth for this reason
(Gantt, 1983). Martin (1983, 1985) overcame this problem in part by devising an
index of ‘‘average enamel thickness’’ that
described the area of the enamel cap divided
by the length of the EDJ. This ratio (c/e)
takes into account shape differences in the
crowns of teeth. Martin (1983, 1985) then
corrected this index for body mass by using
the area of the dentine cap as a measure of
body size. The resulting index of ‘‘relative
enamel thickness’’ can thus be used independently of body size to provide a measure
of enamel thickness for various Miocene and
extant hominoids. Andrews & Martin
(1991) reported on the basis of this
approach that P. major and P. africanus had
thin enamel.
Shellis et al. (1998) have explored both
‘‘relative’’ and ‘‘average’’ enamel thickness
as defined by Martin (1983, 1985) further.
When the area of the dentine cap (‘‘b’’) is
compared across many primates of known
body weight it does scale isometrically and
can therefore justifiably be used to correct
for body weight, although individuals with
teeth that have relatively megadont or
microdont dentine caps with respect to
body size can not be identified when ‘‘b’’ is
used in place of body weight. When average
enamel thickness (c/e) is plotted against
body weight across all primates there are
clear outliers which can be judged to have
either thick or thin enamel. Those with thick
enamel include Daubentonia, Cebus apella
and certain australopithecines. Those with
  
PROCONSUL
195
Figure 15. The relation between average enamel thickness (c/e) to dentine cap area (b) for 45 living and
fossil primate species. Average values for all molars available in each species are used here. Hominoids are
indicated as follows: Hy=Hylobates, R=Rangwapithecus, Pa=Proconsul africanus, Ph=Proconsul heseloni,
Pn=Proconsul nyanzae, Pt=Pan troglodytes, S=Sivapithecus, Pm=Proconsul major, Hs=Homo sapiens,
Po=Pongo, Gg=Gorilla, Aa=Australopithecus africanus, Pr=Paranthropus robustus, Pc=Paranthropus
crassidens, Pb=Paranthropus boisei. Data for Rangwapithecus are from unpublished measurements. Others
are from Martin (1983), Grine & Martin (1988), Andrews & Martin (1991). Ph and Pn, Proconsul heseloni
and Proconsul nyanzae which are the subject of this study are shown in bold. Data for living primates are
presented here in this way with kind permission of Dr Peter Shellis. A fuller analysis of molar enamel
thickness in living primates is given in Shellis et al. (1998).
obviously thin enamel include Varecia
variegata and Gorilla.
When data for ‘‘average enamel thickness’’ (c/e) in molar teeth and body weight
estimates for Proconsul species are plotted in
this way in relation to other primates, none
emerges as an outlier from the reduced
major axis. All species of Proconsul for which
there are data available on ‘‘average enamel
thickness’’ and body weight (from this and
other studies) fall close to the positions
expected for their body weight estimates.
When ‘‘c/e’’ is plotted against ‘‘b’’, none of
the species of Proconsul emerges as an outlier
(Figure 15). From this standpoint Proconsul
cannot be considered to have either thick or
thin enamel in the sense that other outliers
do. Proconsul does, however, have enamel
equivalent in its ‘‘average enamel thickness’’, with respect to log b, to modern
Homo, Sivapithecus and even certain robust
australopithecines reported as by Grine &
Martin (1988). It has enamel that can be
judged marginally thicker than that in Pongo
and Pan but none of these species is an
outlier in the way that Gorilla and Paranthropus boisei are.
Ward & Pilbeam (1983) have previously
argued that it is misleading to regard
primates as having thick or thin enamel. It
may be best they argued, to regard the
majority of primates as having intermediate
enamel thickness but with some having
notably thinner or thicker enamel. Linear
measures of enamel thickness probably
resolve more about functional adaptations
within and between teeth from the same
individual in a way that overall measures of
enamel thickness on the crowns of teeth
cannot (Macho, 1994; Macho & Berner,
1993, 1994; Gantt, 1997; Schwartz, 1997).
It may well be that more information will
emerge that can place the teeth and degree
of enamel thickness in Proconsul into a better
functional and developmental perspective,
but at present it must be said there is no
196
. . 
ET AL.
Figure 16. Striae of Retzius in the cervical region of P. nyanzae and C. apella. In Proconsul the striae
approach 80–90 degrees to the EDJ. In Cebus they are reminiscent of P. boisei and are aligned at a much
reduced inclination to the EDJ. Neither tooth size, body size or enamel thickness therefore, account for
these contrasting stria angles.
good evidence to regard Proconsul as having
thin enamel with respect to other primates
of similar body mass or similar dentine cap
area.
Regardless of what exactly is defined as
‘‘thin’’ or ‘‘thick’’, the enamel in Proconsul
from Rusinga Island appears to be thicker
than that reported for Proconsul from other
early Miocene sites. This may not be surprising in retrospect given the evidence that
Rusinga and Mfangano Island sites were
most similar to dry seasonal forest environments and also had more open conditions
than the tropical, non-seasonal, wet evergreen forest faunas reported for Songhor
and Koru (Andrews, 1996). Although this is
not direct evidence for any differences in
diet between the different species of Procon-
sul the cumulative evidence available so far
suggests there might well have been.
Enamel and dentine morphology
Striae in Proconsul enamel form high angles
to the EDJ especially in the cervical portion
of the lateral enamel. Figure 16 demonstrates the contrast in striae angles at the
cervix of a thick enamelled M2 of C. apella
with those in the M2 of P. nyanzae (RU
1695). The striae in Cebus resemble those
reported in robust australopithecines
(Beynon & Wood, 1986; Grine & Martin,
1988). This comparison suggests that tooth
size, enamel thickness and body size are not
likely to be factors that influence cervical
stria angulation in primate teeth. In general,
the highest mean values for cervical striae
  
angles among living hominoids are found
in Pongo but while there is considerable
variation among hominoids both between
different aspects of the same tooth and
between different tooth types, none
approach those reported here for P. nyanzae.
Some striae in Proconsul are strongly
‘‘S-shaped’’ and resemble those in Pongo
and H. (Symphalangus) syndactylus. Dean &
Shellis (1998) have considered the geometry
of ‘‘S-shaped’’ striae and have proposed a
developmental model to account for their
formation. ‘‘S-shaped’’ striae are formed
when three things occur together. (i) When
daily rates of enamel formation increase
steadily from the EDJ and reach maximal
rates close to the enamel surface. (ii) When
enamel prisms in the same plane as striae
either remain the same width or decrease in
width as they run towards the surface and
(iii) when enamel prisms turn cervically in
their course towards the enamel surface. At
present all that can be said is that the
underlying developmental processes are the
same in the few specimens of Proconsul, H.
(Symphalangus) syndactylus and Pongo that
have been studied. In the future it will be
interesting to report on ‘‘S-shaped’’ striae in
other extant primates and fossils such as
Lufengpithecus and Sivapithecus.
While the pattern of increase in cuspal
enamel formation rates appears to resemble
that documented here for M2s in Pan and
Homo, the fast rates of enamel formation in
outer lateral enamel resembles in Pongo.
Cross striation repeat intervals between
regular striae of Retzius in humans and great
apes and in Papio and Theropithecus (and in
one siamang available to us) are usually in
the range of 7–9 days with outliers recorded
at six and 11 days or more (Swindler &
Beynon, 1992; Dean, 1995b; FitzGerald,
1995; Reid & Dirks, 1997). Intervals in
macaques are reported to be four or five
days (Bowman, 1991) and they are four
days based on a limited sample of gibbons
(Dirks et al., 1995). It appears that the
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197
repeat intervals in these specimens of P.
heseloni are closer to those known for small
species of gibbons and small monkeys.
Those in P. nyanzae are hard to interpret in
the absence of more data. Larger samples of
teeth from different individuals may extend
the range of these counts in both species and
data for larger samples of great apes in
particular are needed.
Of the primates studied so far, the greatest
rate of dentine formation occurs in the tallest cusps of teeth (Dean, 1995b; Dean &
Scandrett, 1995, 1996; Liversidge et al.,
1993). Low squat tooth crowns are likely to
have slower rates of dentine formation than
tall crowns with high cusps. Their spacing
reveals slow daily rates of cuspal dentine
formation in premolar and molar teeth.
They are below the range known for humans
and modern great apes. They are also below
the range of daily cuspal rates of dentine
formation determined experimentally in
macaques (Bowman, 1991; Dean, 1993;
Molnar et al., 1981). In all these primates
cuspal rates of dentine formation are closer
to 4 or 6 ìm per day. However, the
measurements in both species of Proconsul
match measurements made in the same way
and in the same tooth types of H. moloch. In
the gibbon M2, for example, the mean value
for the spacing of daily lines was 2·6 ìm
(S.D.=0·23, range=2·3–3·2).
The combined effect of large fast rates of
enamel formation at the EDJ and slow rates
of dentine formation at the EDJ in both
P. heseloni and P. nyanzae give these teeth
a unique histological appearance at the
cervical EDJ. Interestingly, Andrews &
Martin (1991) illustrate sections of other
Miocene hominoids and some (e.g., Heliopithecus) appear, at least superficially, similar
to Proconsul in this respect. A constant
extension rate in both enamel and dentine at
the EDJ is maintained by combining a very
low angle of inclination of the mineralizing
front in the dentine with a very high angle
of inclination of the mineralizing front in
198
. . 
ET AL.
Figure 17. Accentuated lines in the enamel and dentine of the P. heseloni adult M1 (a) and a human M1
(b). Each of these pairs of lines were formed at the same time in enamel and dentine. They demonstrate
the ratio of dentine formed to enamel over the same time period.
enamel. The small angle of inclination of the
mineralizing dentine front (Angle D as
defined by Shellis, 1984) is directly related
to the slow rate of dentine formation. Figure
17 illustrates the difference in the ratio of
dentine formed to enamel in Homo and in P.
heseloni in the lateral cuspal region of identical tooth types (M1) in each. These findings all confirm that some daily increments
in Proconsul dentine were nearly three times
smaller than the equivalent daily increments
in enamel growing at the same time in
cervical regions.
Both molar teeth attributed to P. nyanzae
have what appear to be regular accentuated
markings in the coronal dentine (Figure 18).
This is also true for several of the teeth
attributed to P. heseloni but in particular for
  
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199
Figure 18. Regular accentuated lines in the dentine of the M2 of P. nyanzae. In this tooth these longer
period lines are spaced approximately 90 days apart and are of unknown aetiology.
the M2 germ. Measurements between these
lines made in the midline axial plane of the
dentine and divided by the daily rate of
dentine formation measured in this position
in these teeth gives some idea of the timespan between them. In the larger P. nyanzae
teeth there are about nine or ten lines which
are spaced between 90 and 100 days apart.
In the smaller P. heseloni teeth there are six
or so lines which are between 50 and 55
days apart. Other teeth from this sample also
show accentuated markings, but none that
can be measured over such a long period as
in these three teeth. It seems possible that a
complex pattern of quite widely spaced
markings may recur through several teeth, of
the kind identified by Macho et al. (1996)
in Theropithecus and tentatively linked with
seasonal changes about 2 m.y.a. at Koobi
Fora in northern Kenya. Perikymata on the
tooth surfaces of P. heseloni and P. nyanzae
teeth also show evidence of regular linear
markings. At present however, it is idle to
speculate about the likelihood of either a
possible physiological cause (perhaps related
to body size) or a possible cause related to
seasonality. There is nevertheless great
potential to bring together information
about the palaeoecology of Miocene primate
localities, about microwear patterns on the
teeth of different species of Miocene
hominoids and about patterns of seasonality
and stress from other causes that might be
determined from accentuated markings in
fossil enamel and dentine (Andrews, 1996;
Walker et al., 1994; Macho et al., 1996).
The juvenile tooth germs
The results of this study confirm that all but
one of the tooth germs that are described
as belonging to the juvenile P. heseloni
Individual IV are compatible with each
other and might have belonged to an infant
about one year old at death. The M2 germ
however, had been forming for 1·35 years
(using the data derived from dentine), but
according to the dental development
sequence proposed in this study M2 might
not be expected to have begun to mineralize
until 10 months of age or so. This suggests
the M2 germ may have belonged to another
infant that was just over two years old at
death.
It is also notable that the M1 crown of this
infant has no root preserved, but dentine is
completely formed to the level of the enamel
200
. . 
ET AL.
Figure 19. Composite summary chart of dental development in P. heseloni based on the maximum values
of crown formation times presented in Table 6, the calculated rates of root extension summarized in Table
5, and the information about the sequence of dental development summarized in Figure 17. Solid lines are
crown formation times and dashed lines are root formation times. The following additional key points
were used in constructing this chart: (i) the neonatal line in M1 indicates formation began 30 days before
birth, (ii) the neonatal line in dm2 indicates formation began 60 days before birth, (iii) root extension rates
suggest the dm2 root took 200 days to form, (iv) dentine formation times indicate I2 formation began 12
days after I1, (v) the absence of a neonatal line in dm1 enamel suggests crown completion occurred before
birth in this tooth, (vi) root extension rates suggest premolars and molars take between 2·3 years and 3
years to complete root formation, (vii) root lengths in Proconsul suggest M1 roots take longer to form than
M2 roots and that M3 roots take the longest time to form, (viii) in this study we estimate 2·3 years for M1,
2·7 years for M2 and 3·0 years for M3 root formation for P. heseloni. The overlap of M3 with M2 crown
formation is an estimate.
cervix (see Figure 1). This implies that there
was actually some root formation, although
there is no occlusal wear to suggest this
tooth was in functional occlusion. No direct
estimates of crown formation time were
possible for this tooth but based on this
evidence and other crown formation time
estimates for the first permanent molar,
combined crown and root formation times
might have been greater than one year.
This M1 crown is also a little different in
morphology to the other M1 crown of the
adult individual (see Figure 4). It is tall
and narrow and not so broad and squat.
The angles of the striae to the EDJ are
higher than for other Proconsul molar teeth
sectioned here, especially in the cervical
region, and judged from the long-period
striae in the cuspal dentine it had dentine
formation rates that exceed those observed
in other posterior teeth (but which are
compatible with the taller cusps).
The period of dental development in Proconsul
Figure 19 is a composite reconstruction of
dental development in P. heseloni and
summarizes the developmental sequences,
the crown formation periods and the root
formation periods estimated histologically
and from perikymata counts. In this chart
we have used the greatest of the mean values
calculated as they appear in Table 6.
(Additional key points used to construct this
chart are given in the legend to Figure 19.)
It seems reasonable on this basis to assume
that dental development in P. heseloni took
between six and seven years. It is important
to stress that this estimate is to the end of
M3 root completion and that this differs
from estimates for the period of dental
  
development quoted for other primates
which are based on gingival emergence of
M3 (Smith, 1989).
No fundamental differences in dental
development between the three great apes
have yet been identified. This suggests that
differences in body size or tooth size appear
to have little obvious effect on the period of
dental development. It is also not clear how
body weight or tooth size influence the
period of dental development in extant Old
World monkeys, although some differences
exist in the dental development period
between small macaques and larger baboons
(Bowen & Koch, 1970; Reid & Dirks, 1997;
Smith 1989; Smith, 1994; Smith et al.,
1994; Swindler, 1985). Furthermore, we
know very little about dental development in
siamangs and gibbons Dirks (1998). These
differ in both body weight (Ruff et al., 1989;
Raemakers, 1984) and tooth size. All this
makes it difficult to place the estimate for
the total period of dental development in P.
heseloni into perspective except to say 6–7
years is well below the known period of time
it takes great ape dentitions to complete.
Body weight estimates for P. nyanzae
are broadly equivalent to those of female
chimpanzees of the smaller sub-species. The
molar crown formation times estimated here
for M1 and M2 fall short of the times estimated for all great apes using histological
techniques identical to those used here
(Beynon et al., 1991; Chandrasekera et al.,
1993; Reid et al., 1998). On this basis, the
period of dental development to the end of
M3 root formation was unlikely to have
exceeded eight years in P. nyanzae. While
the data for P. nyanzae are scant, if the
crown formation times estimated for the M1
and M2 reported here are close to the average for P. nyanzae then these times fall short
of average values for six individuals of P.
troglodytes by between 30% and 40% and
exceed those for four individuals of Papio
anubis (body weight 11 kg) by 15%–20%
(Reid & Dirks, 1997; Reid et al., 1998).
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201
While this might be suggestive of a shorter
period of dental development in P. nyanzae
than in Pan, data on root extension rates are
needed to place estimates of M1 emergence
into a secure comparative context.
The first permanent molar is a good overall indicator of several life history parameters
on, e.g., regresion plots that include large
numbers of primate species, but Smith et al.
(1995) and Smith & Tompkins (1995) note
that interspecific regressions are poor
predictors of individual specific differences.
We know already, for example, that robust
australopithecines were more than likely
weaned before they erupted M1 from the
tooth wear present on deciduous molars at
M1 crown completion only (Aiello et al.,
1991). We know also that first reproduction
in macaques may occur while they are still
growing their M3 roots as Bowman (1991)
has observed parturition lines of known history in macaques, but that gibbons do not
reproduce until well after third molar root
development is complete. Many significant
observations about life history cannot be
tightly predicted from dental development
and even skeletal development and epiphyseal fusion do not follow a common
sequence with dental development across
primates (Watts, 1985; Winkler, 1996).
Nonetheless, a knowledge of dental development provides the most important maturational profile available for fossil primates.
Kelley (1997) has concluded, on the
basis of perikymata counts on a developing
central incisor, that the age of M1 emergence in Sivapithecus parvada was within the
ranges of the extant great apes. It follows
that S. parvada would have had a maturational profile that approached those of
modern great apes. Kelley (1997) also noted
that the large brain size and especially body
sizes of the proconsulids compared with
earlier catarrhines and contemporaneous
nonhominoids are perhaps indicative of
the beginning of a prolonged life history.
Further evidence for this was suggested
202
. . 
from the estimated mean age of M1 emergence based on data for brain size and M1
emergence in 23 species of primates (Kelley,
1997). In P. heseloni, M1 emergence was
estimated at 20·6 months with an approximate range for the mean (based on the
confidence interval for brain size rather than
the error of the estimate) of between 19·6
and 21·6 months. Kelley (1997) concluded
that this age for M1 emergence falls at the
upper end of the range of means for all
extant nonhominoid catarrhines, many of
which are considerably larger on average
than P. heseloni. On this evidence Kelley
(1997) has cautiously suggested these
results indicate a more prolonged life history
for P. heseloni. But a considerable grade shift
may occur between Old World monkeys and
hominoids in many life history traits and in
dental development and predictions based
only on hominoid brain sizes, for example,
might result in estimates of M1 emergence
in P. heseloni in excess of those cited here.
Estimates for M1 crown formation time in
P. heseloni in this study are around 14
months after birth (approximately 30 days of
M1 formation occurred before birth). If root
extension occurred at the same rate as in M2
and P4 at an average 6·4 ìm per day (and
poor data from one M1 section suggests this
is likely) then M1 would have just less than
1·25 mm of root formed at 20·6 months but
close to 1·5 mm formed at 21·6 months.
These predictions are speculative but not
incompatible with the predictions of Kelley
(1997) based on 23 species of primates.
Future studies on dental development in P.
nyanzae and P. major might result in good
estimates for the age of emergence of M1 in
these larger bodied proconsulids and so provide a better idea about the affects of body
size and tooth size on dental development
within Proconsul. This would make it easier
to judge whether there is evidence that
dental development and the overall maturational profile was prolonged in Proconsul.
Histological studies on other Miocene pri-
ET AL.
mates such as Victoriapithecus, Sivapithecus
and Lufengpithecus will also place the results
of this study into a better phylogenetic
perspective. It remains likely, however, that
postcranial, masticatory and life history
traits evolved in a mosaic fashion (Rae,
1997). Of these traits, those that probably
resulted from reduced adult mortality rates
(which include a prolonged developmental
period and a bigger brain) are likely to have
been the last to appear.
Conclusions
This is the first histological study of
Proconsul teeth from Rusinga Island, Kenya.
A chronology of the sequence of tooth
development in P. heseloni indicates M3 root
formation was complete between 6 and
7 years in this siamang-sized Miocene
primate. Crown formation times in an M1
and M2 attributed to the larger female
chimpanzee-sized P. nyanzae were between
30% and 40% less than the average values
for seven common chimpanzees studied in
the same way. The results reported here
suggest that both species of Proconsul from
Rusinga Island had thicker enamel than previously described for P. africanus and P.
major from other older sites in western
Kenya and Uganda. Reports on the palaeoecology of Miocene sites on Rusinga
together with future research on the evidence for seasonality from accentuated
markings in teeth and from tooth microwear
studies may allow us to place studies of
enamel thickness in Proconsul into a more
secure dietary and functional context.
Certain microstructural features in enamel
and dentine appear, so far, to be unique to
Proconsul. P. nyanzae appears more derived
with respect to P. heseloni in the degree to
which these unique features are expressed.
Rates of enamel formation close to the EDJ
are higher than in other primates studied so
far. The ratio of dentine to enamel formed
close to the EDJ in the lateral aspects of the
  
crown are greater than 1:2 and as much as
1:3 in some P. nyanzae teeth. The pattern of
increase in enamel formation rates during
molar cusp formation in Proconsul most
resembles Pan and Homo. In several other
features Proconsul most resembles Pongo.
These include high stria angles to the EDJ,
fast rates of enamel formation in lateral
enamel (and therefore relatively widely
spaced striae of Retzius) and the occasional
presence of ‘‘S-shaped’’ striae in lateral
enamel. Rates of dentine formation are slow
in Proconsul compared with the majority of
other extant primates studied so far and may
be related to the low squat cusp and crown
morphology. Cuspal rates of dentine formation do however, closely resemble those
in Hylobates species reported here. Overall,
the microanatomical features of Proconsul
enamel and dentine resemble those in extant
hominoids with a few features unique to
Proconsul and appear only to resemble some
extant New and Old World monkeys in the
cross striation repeat interval of 5 or 6 days
between regular striae of Retzius. Ongoing
studies of extant great apes, gibbons and
monkeys and of other Miocene primates
will provide interesting answers to many
questions that have arisen from this study.
Acknowledgements
We thank the Government of Kenya and the
Governors of the Kenya National Museums
for granting us permission to use valuable
fossil material in their care. Once again,
Emma Mbua and the Department of
Palaeontology, Kenya National Museum,
helped greatly with this project. We are
grateful to Alex Bedborough, Ian Bell,
Louise Humphrey, Jane Pendjiky, Chris
Sym, and James Weir for technical and
photographic assistance. We thank the following for their help and support with
aspects of this project and for helpful discussions on topics related to it. Leslie Aiello,
Peter Andrews, Wendy Dirks, Susan Evans,
PROCONSUL
203
David Gantt, Jay Kelley, Gabriele Macho,
Terry Harrison, Paul O’Higgins, Todd Rae,
Kathy Rafferty, Fernando Ramirez Rozzi,
Gary Schwartz, Peter Shellis, Holly Smith,
Fred Spoor and Daris Swindler. We are
especially grateful to the associate editor and
the referees for their many thoughtful and
constructive comments on the manuscript.
This study was supported by The Royal
Society, The Leverhulme Trust and the
National Science Foundation.
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RU 7290
RU 7290
RU 7290
RU 7290
FT 49
RU 1685
RU 7290
RU 7290
RU 1716
RU 7290
FT 3637
RU 2031
RU 7290
RU 7290
RU 1716
SO 396
RU 7290
RU 7290
RU 7290
RU 7290
RU 7290
RU 7290
RU 1733
RU 1733
RU 7290
P.
P.
P.
P.
P.
P.
P.
P.
P.
P.
P.
P.
P.
P.
P.
P.
P.
P.
P.
P.
P.
P.
P.
P.
P.
heseloni
heseloni
heseloni
heseloni
nyanzae
nyanzae
heseloni
heseloni
nyanzae
heseloni
heseloni
nyanzae
heseloni
heseloni
nyanzae
major
heseloni
heseloni
heseloni
heseloni
heseloni
heseloni
heseloni
heseloni
heseloni
Accession
number
Species
Appendix 1
LLI1
LLI1
ULI1
URI1
ULI1
ULI1
LLI2
LRI2
LLI2
ULI2
URI2
URI2
LLC
LLC
LLC
LRC
ULC
URC
LLP3
LLP3
LLP4
LLP4
ULP4
ULP4
LLM1
Tooth
type
B
B
B
B
B
B
B
B
B
B
B
B
B
B
B
B
B
B
B
B
B
B
B
B
MB
Tooth
aspect
(12)
(12)
(13)
(13)
6
3
8
(11)
2
(9)
(9)
2
3
9
8
(12)
(10)
(12)
10
10
6
6
10
10
6
Cusp
15
(12)
(14)
(13)
6
7
11
(13)
8
(12)
(12)
12
9
9
8
(12)
13
(15)
10
15
10
10
11
8
10
15
(12)
(17)
(14)
7
9
13
(14)
8
17
17
14
16
13
10
(12)
15
15
15
12
14
14
13
16
13
16
16
17
(17)
8
9
14
(17)
10
17
14
14
16
15
12
(12)
16
17
16
15
15
15
21
12
16
(17)
17
(17)
17
10
11
17
17
13
17
12
18
16
15
12
(13)
17
17
16
16
14
16
27
16
(17)
(17)
(19)
17
11
12
18
17
15
16
(20)
21
20
16
12
13
17
18
16
15
18
18
23
15
14
(19)
(19)
(20)
(19)
12
16
19
19
17
(20)
(20)
21
24
20
15
15
17
16
20
20
(20)
(20)
(20)
(20)
11
16
(20)
(20)
17
26
20
18
18
(19)
(19)
(20)
(20)
(20)
(20)
13
14
20
(20)
17
(18)
26
20
16
15
17
(19)
16
12
20
(20)
20
20
18
15
(19)
(20)
(20)
(20)
13
16
14
(20)
(20)
14
Perikymata per mm of tooth crown height
14
12
12
10
12
(12)
(12)
Cervix
(151)
(145)
(157)
(170)
(104)
(150)
(140)
(168)
(167)
(108)
(104)
(120)
156
157
161
(261)
(160)
(148)
103
103
77
79
105
91
45
Sum of
stria
2·07
1·99
2·15
2·33
1·71
2·46
1·92
2·30
2·75
1·48
1·71
1·97
2·14
2·15
2·65
4·29
2·19
2·03
1·41
1·41
1·05
1·08
1·44
1·25
0·62
Years
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SO 396
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RU 2087
RU 2087
RU 2087
RU 2087
RU 1820
RU 1931
RU 7290
RU 1820
RU 1931
RU 1820
RU 1931
RU 1820
RU 1931
SO 396
P.
P.
P.
P.
P.
P.
P.
P.
P.
P.
P.
P.
P.
P.
P.
P.
P.
P.
P.
LLM1
LLM1
LLM1
LLM2
LLM2
LLM2
LLM2
LLM2
LLM2
LLM3
LLM3
LLM3
LLM3
LLM3
LLM3
LLM3
LLM3
LLM3
LLM3
Tooth
type
DB
DL
MB
DL
DB
MB
ML
DB
DL
MB
MB
MB
ML
ML
DB
DB
DL
DL
MB
Tooth
aspect
6
6
6
2
2
6
6
(8)
6
14
(20)
2
16
14
6
(20)
20
2
6
Cusp
11
10
11
8
6
6
16
(13)
6
24
24
6
24
20
(14)
(20)
22
7
6
13
14
11
12
12
16
17
20
10
31
(24)
13
24
24
20
20
(24)
15
13
24
17
16
21
(24)
24
20
26
22
16
16
16
16
20
28
24
(23)
14
13
24
16
20
27
Perikymata per mm of tooth crown height
Cervix
46
46
57
62
56
56
63
(64)
85
69
(68)
66
(108)
58
(66)
(60)
(66)
48
78
Sum of
stria
0·75
0·75
0·94
0·85
0·77
0·92
1·03
1·05
1·40
0·95
0·93
0·90
1·48
0·79
0·90
0·82
0·90
0·66
1·28
Years
Perikymata counts for P. heseloni and P. nyanzae made per millimetre of tooth length on all aspects of tooth surfaces that preserve them. Figures in parentheses indicate that a millimetre of
tooth surface did not preserve some or any perikymata. The total perikymata number representing the complete lateral enamel formation time (in years) appears in the last but one column.
Values for P. heseloni were calculated using a cross striation repeat interval of 5 days (recorded for all specimens in this study). A value of 6 days was used for the larger P. nyanzae and P. major
specimens included.
nyanzae
nyanzae
major
heseloni
heseloni
nyanzae
nyanzae
nyanzae
nyanzae
heseloni
heseloni
heseloni
heseloni
heseloni
heseloni
heseloni
heseloni
heseloni
major
Accession
number
Continued
Species
Appendix 1
  
209
PROCONSUL
Appendix 2
Species
Accession
number
Tooth
type
Tooth
aspect
Total
perikymata
Lat. ena.
form.
(yrs)
Cuspal
form.
(yrs)
Crown
form.
(yrs)
P.
P.
P.
P.
P.
P.
P.
P.
P.
P.
P.
P.
P.
P.
P.
P.
P.
P.
P.
P.
P.
P.
P.
P.
P.
P.
P.
P.
P.
P.
P.
P.
P.
P.
P.
P.
P.
P.
P.
P.
P.
P.
P.
P.
P.
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RU 7290
RU 7290
RU 7290
RU 7290
RU 7290
FT 3637
RU 7290
RU 7290
RU 7290
RU 7290
RU 7290
RU 7290
RU 1733
RU 1733
RU 7290
RU 7290
RU 7290
RU 7290
RU 7290
RU 1820
RU 1931
RU 1820
RU 1931
RU 1820
RU 1931
RU 1820
RU 1931
RU 7290
RU 1716
FT 49
RU 1685
RU 1716
RU 2031
RU 2087
RU 2087
RU 1721
RU 2087
RU 2087
RU 2087
RU 2087
SO 396
SO 396
SO 396
LL I1
LR I1
UL I1
UR I1
LL I2
LR I2
UL I2
UR I2
LL C
LR C
UL C
UR C
LL P3
LL P3
UL P4
UL P4
LL P4
LL P4
LL M1
LL M2
LL M2
LL M3
LL M3
LL M3
LL M3
LL M3
LL M3
LL M3
LL M3
LL M3
LL C
UL I1
UL I1
LL I2
UR I2
LL M1
LL M1
U M1
LL M2
LL M2
LL M2
LL M2
LR C
LL M1
LL M3
B
B
B
B
B
B
B
B
B
B
B
B
B
B
B
B
B
B
MB
DL
DB
DB
DB
DL
DL
MB
MB
ML
ML
MB
B
B
B
B
B
DB
DL
B
DB
DL
MB
ML
B
MB
MB
151
145
157
170
140
168
108
104
156
157
160
148
103
103
105
91
77
79
45
62
56
66
60
66
48
69
68
108
58
61
161
104
150
167
120
46
46
65
64
85
56
63
261
57
78
2·07
1·99
2·15
2·33
1·92
2·30
1·48
1·42
2·14
2·15
2·19
2·03
1·41
1·41
1·44
1·25
1·05
1·08
0·62
0·85
0·77
0·90
0·82
0·90
0·66
0·95
0·93
1·48
0·79
0·84
2·65
1·71
2·47
2·75
1·97
0·76
0·76
1·07
1·05
1·40
0·92
1·03
4·29
0·94
1·28
0·22
0·22
0·33
0·33
0·33
0·33
0·33
0·33
0·42
0·42
0·42
0·42
0·42
0·42
0·42
0·42
0·42
0·42
0·44
0·50
0·50
0·78
0·78
0·78
0·78
0·78
0·78
0·78
0·78
0·78
0·43
0·33
0·33
0·33
0·33
0·9
0·9
0·9
0·93
0·93
0·93
0·93
0·42
0·9
0·93
2·29
2·21
2·48
2·66
2·25
2·63
1·81
1·75
2·56
2·57
2·61
2·45
1·83
1·83
1·86
1·67
1·47
1·50
1·06
1·35
1·27
1·68
1·60
1·68
1·44
1·73
1·71
2·26
1·57
1·62
3·06
2·04
2·8
3·08
2·3
1·66
1·66
1·97
1·98
2·33
1·85
1·96
4·71
1·84
2·2
heseloni
heseloni
heseloni
heseloni
heseloni
heseloni
heseloni
heseloni
heseloni
heseloni
heseloni
heseloni
heseloni
heseloni
heseloni
heseloni
heseloni
heseloni
heseloni
heseloni
heseloni
heseloni
heseloni
heseloni
heseloni
heseloni
heseloni
heseloni
heseloni
heseloni
nyanzae
nyanzae
nyanzae
nyanzae
nyanzae
nyanzae
nyanzae
nyanzae
nyanzae
nyanzae
nyanzae
nyanzae
major
major
major
Mean cr.
form
(yrs)
2·25
2·57
2·44
1·78
2·57
2·53
1·83
1·77
1·28
1·06
1·31
1·68
3·06
2·42
2·69
1·76
2·03
4·71
1·84
2·2
Kenya National Museum accession numbers are given for all the P. heseloni, P. nyanzae and P. major specimens where it was
possible to count perikymata. The total perikymata counts from the last but one column of Appendix 1 are given for the tooth
aspect indicated buccal (B) for anterior teeth, mesiobuccal (MB), mesiolingual (ML), distobuccal (DB) or distolingual (DL).
These times (in years) for lateral enamel formation times were derived by multiplying the number of perikymata by five for P.
heseloni or by six for P. nyanzae and P. major. Cuspal enamel formation times are derived from the histological sections and the data
presented in Table 2. Individual crown formation times for each tooth have been estimated as the sum of cuspal enamel formation
time (specific for each tooth type) and lateral enamel formation times as calculated here in column 6. The mean crown formation
time in the last column for P. heseloni is either (i) for incisors, canines and premolar teeth, the mean of all teeth belonging to one
specimen or more of a tooth type, or (ii) for molar teeth of P. heseloni the mean of all crown formation times calculated using only
the mesiobuccal cuspal formation times and mesiobuccal perikymata counts. Mean crown formation times for P. nyanzae are an
average for all cusps where enamel formation times could be calculated for M1 and M2 separately using cuspal data from Table 2.
The cuspal data for P. nyanzae were also used for the few P. major teeth included in this Appendix.