Comparative dental development and microstructure of ... - UCL

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 

Keywords: Proconsul, Miocene 

hominoids, enamel 

thickness, Striae of Retzius, 

enamel, dentine. 

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 μm 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 

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. 

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; 

0047–2484/98/070163+47$30.00/0 1998 Academic Press

164 A. D. BEYNON ET AL. 

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 P 3 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 

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

DENTAL DEVELOPMENT IN PROCONSUL 

165 

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 development 

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 (I 1 ,I 2 , 

M 1 and M 2 ) and two deciduous mandibular 

teeth (dm 1 and dm 2 ), 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


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: dm 1 buccal view, dm 2 lingual view, M 1 

occlusal view. Middle row left to right: dm 1 occlusal view, dm 2 occlusal view, M 1 , fractured base of crown. 

Bottom row left to right: I 2 germ, I 1 germ, M 2 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


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, M 1 occlusal view, M 1 mesiobuccal 

view. Middle row: base and incomplete lingual aspect of canine. Bottom row: occlusal views of P 3 ,M 2 and 

M 3 . 

(Individual III from the Kaswanga Primate 

Site on Rusinga Island) were also prepared 

for histological examination (Figure 2). 

These were a canine, P 4 ,M 1 ,M 2 and M 3 

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 M 1 

and a right M 2 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


Figure 3. P. nyanzae M 1 (RU 1721) and M 2 (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


169 

(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. 

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 dm 1 ,dm 2 ,I 1 ,I 2 ,M 1 and M 2 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 μm (range 99 to 155 μm 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


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: dm 1 ,dm 2 ,I 1 ,I 2 ,M 1 ,M 2 (juvenile 

P. heseloni) andM 1 . Row 3: canine P 4 ,M 3 (adult Proconsul heseloni). Bottom row: M 1 and M 2 (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.


171 

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 

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 M 2 , 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 M 2 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


173 

molars of P. nyanzae, H. sapiens, Pan 

troglodytes, G. gorilla, Pongo pygmaeus, H. 

moloch and T. gelada. Data for a modern 

human dm 2 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, 

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 μm in both micrographs.)


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 

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


175 

Figure 6. Daily lines in dentine in (a) the midline axial plane of the cusp of a juvenile M 1 of P. heseloni 

and (b) daily lines in the cervical dentine of the adult permanent M 1 . (Transmitted light. Original 

magnification 500. Fieldwidth 120 μm 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


(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 P 3 s, 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 

P 4 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 

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 dm 2 

of the juvenile specimen and in the M 1 ,M 2 

and P 4 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 dm 2 ,M 1 ,I 1 and I 2 

germs of the juvenile specimen revealed neonatal 

lines in the dm 2 and M 1 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 M 1 , 

I 1 and I 2 also allowed these teeth to be 

securely registered with each other. Since


177 

Figure 7. Incremental markings in the cervical dentine of the P. heseloni P 4 (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 M 1 ,P 4 and M 2 

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


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 


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 I 1 and 52% in I 2 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 

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 M 2 

(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 μm, 4·8 μm and 5·4 μm 

respectively and an overall average value 

(4·9 μm) of these three means used as the 

cuspal mean. Cuspal enamel thickness was 

measured as 1600 μm in this cusp, along 

the prism direction, which when divided by 

4·9 μm 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 dm 2 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


179 

Table 1 

Index number of 

each section 

(m=mesial; 

d=distal) 

Tooth 

type 

Average 

enamel 

thickness 

(c/e) 

Relative 

enamel 

thickness 

{(c/e)/b}100 

Linear 

enamel 

thickness 

measurement 

No. 2 

(mm) 

Linear 

enamel 

thickness 

measurement 

No. 3 

(mm) 

Linear 

enamel 

thickness 

measurement 

No. 4 

(mm) 

Linear 

enamel 

thickness 

measurement 

No. 5 

(mm) 

Linear 

enamel 

thickness 

measurement 

No. 6 

(mm) 

Linear 

enamel 

thickness 

measurement 

No. 7 

(mm) 

Juvenile 

P. heseloni 

HT3/91E LR dm2 0·36 10·5 

HT3/91F m LR M1 0·68 16·4 0·88 0·87 0·9 0·64 0·64 

HT3/92G m LR M2 0·98 19·1–24·4 1·18 1·11 1·3 1·3 1·04 0·94 

Adult 

P. heseloni 

HT2/91B LR P4 0·65 13·4 0·84 

HT2/91C m LR M1 

HT2/91C d LR M1 0·62 14·4 0·82 0·87 

HT2/91D m LR M2 

HT2/91D d LR M2 0·89 

HT2/91E m LR M3 0·81 17·0 0·93 

HT2/91E d LR M3 0·99 21·2 1·17 1·34 0·88 0·88 

Adult 

P. nyanzae 

RU 1721 m RM1 1·65 1·58 1·52 1·44 1·61 1·60 

RU 1721 d RM1 1·44 27·6 1·61 1·76 1·76 1·74 

RU 1695 m RM2 1·19 22·4 

RU 1695 d RM2 1·25 22·3 1·5 1·57 1·56 1·17 1·32 

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.)


Table 2 

Index No. of 

tooth section 

m=mesial; 

d=distal 

Tooth 

type 

Occlusal 

enamel 

thickness 

along prisms 

(microns) 

Cuspal 

formation time 

(=occl. enam. thick/4·9 μm) 

(days) 

Total 

striae 

counts 

(Lingual) 

Total 

striae 

counts 

(Buccal) 

Range of 

lateral enamel 

form. time 

estimates 

(days) 

Range of 

total crown 

formation 

estimates 

(days) 

Crown formation 

time (cusp+lat.). 

The lateral aspect 

or cusp used is 

shown in parentheses 

(years) 

Juvenile 

P. heseloni 

HT3/91A LR I1 400 82 40+ 200 282 0·77+ (b) 

HT3/91B LR I2 600 122 35+ 175 297 0·81+ (b) 

HT3/91D LR dm1 

HT3/91E m LR dm2 

HT3/91F m LR M1 780 159 

HT3/91G m LR M2 900 184 24+ 22+ 120 304 0·8+ (mb) 

Adult 

P. heseloni 

HT2/91A LR C 750 153 142+ 710 863 2·4+ (b) 

HT2/91B LR P4 750 153 80 109 400–545 553–698 1·9 (b) 

HT2/91C m LR M1 800 163 87 54+ 435–270 433–598 

HT2/91C d LR M1 800 163 66+ 51+ 255–330 418–493 1·2 (mb) 

HT2/91D m LR M2 (900) (184) 70+ 66+ 330–350 514–534 1·4 (mb) 

HT2/91D d LR M2 77 385 

HT2/91E m LR M3 1400 286 65+ 61+ 305–325 591–611 1·6 (mb) 

HT2/91E d LR M3 1400 286 82 410 696 

Adult 

P. nyanzae 

RU 1721 m URM1 1570 320 69 414 734 2·0 (mb) 

RU 1721 d URM1 1600 327 56 336 663 1·8 (db) 

RU 1695 m LRM2 1600 327 72 432 759 2·1 (mb) 

RU 1695 d LRM2 1717 350 63 96 378–576 728–926 2·0 (dl)–2·5 (db) 

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 μm. 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 M 2 section (HT2/91D dist.) no cuspal enamel formation 

time could be estimated and values for M 2 were used for the unworn M 2 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.


181 

Figure 8. Plots of measurement of cuspal enamel cross striation spacings (μm) in Hylobates moloch, Gorilla, 

Theropithecus and a human dm 2 . 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 μm per day to higher values of between 

5or6μm per day. Only in Hylobates moloch is there a slowing of the outer enamel layer.


Figure 9.


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 M 2 cuspal enamel. 

Figure 10 shows box plots for rates of 

enamel formation in two molar tooth cusps 

of Pongo (one mesiobuccal cusp of an M 2 

and one mesiobuccal cusp of an M 3 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. InPongo, 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 A. D. BEYNON ET AL.


185 

5–10% of the mean values for four methods 

used (Dean, 1998). Thus in humans, M 2 

cuspal enamel in the second permanent 

molar takes about 16 months to form 

(Figure 9). By way of contrast, human M 3 

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 M 2 s, 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 M 2 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 μm at the 

enamel–dentine junction (EDJ) and approach 

7 μm 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 M 2 

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 μm 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 

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 μm 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 M 1 s 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. Inthe 

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 M 2 andanM 3 of Pongo pygmaeus. In these two plots 

cross striation spacings rise swiftly from 2 μm or3μm per day to values around 5 μm 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.


Table 3 

Comparative data for stria angles and stria widths in M1 only 

Taxon 

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. 

Homo sapiens 20 13·01·5 27·02·6 32·0 1·8 

Pan troglodytes 23 9·01·8** 26·06·0 31·0 4·3 

Pongo pygmaeus 10 9·03·7* 30·07·1 41·0 5·6** 

Gorilla gorilla 28 7·03·1** 23·06·8* 31·010·7 

Proconsul heseloni 1/2 12–28 18–21 28–45 

Proconsul nyanzae 1 16 21–30 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. 

Homo sapiens 20 37·02·8 28·03·2 21·0 3·5 

Pan troglodytes 21 28·01·6** 27·02·1 20·0 2·7 

Pongo pygmaeus 10 54·03·2** 47·07·7** 30·0 4·7** 

Gorilla gorilla 28 42·05·0** 33·05·3** 27·0 4·6** 

Proconsul heseloni 1/2 46 32–41 26 

Proconsul nyanzae 1 28 25 

Significance with respect to Homo; *P


187 

Figure 11. ‘‘S-shaped’’ striae in the cervical enamel of the P. nyanzae M 2 (left) and the P. heseloni M 1 

(right). 

(Individual IV) they measured 25 μm apart 

maximally. In the high cusped M 1 germ 

(Individual IV) 16·7 μm apart maximally, 

and in other lower crowned premolars and 

molars (Individual III) they measured on 

average 12·5 μm 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 μm per day in the I 1 , 3·3 μm per 

day in the high cusped M 1 and 2·5 μm 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 dm 1 and the 

dm 2 (Individual IV) had measurable daily 

lines in the coronal dentine of around 

3·5 μm. Measurements made through the 

whole thickness of the cuspal dentine in two 

P. heseloni teeth (M 2 and M 3 ), 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 M 2 was 2·4 μm 

(S.D.=0·21, range=1·95–2·66). For the M 3 

(n=14) the mean value was 2·09 μm


Figure 12. Confocal light image of striae of Retzius and enamel cross striations in the cervical region of the 

P. nyanzae M 2 . There are six cross striations between adjacent striae. (Fieldwidth 360 μm.) 

(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 μm or less. Values around 

2 μm 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 dm 2 (Individual IV) and the M 1 

(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 μm per day) closely matches 

the rate of enamel formation (4·0 μm 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


189 

Table 4 

Index No. of 

tooth section 

m=mesial; 

d=distal 

Tooth 

type 

Enamel stria 

EDJ angles 

(degrees) 

Dentine to 

enamel ratios 

at the EDJ or 

occlusally (occ.) 

if indicated 

Mean axial 

long-period 

dentine 

lines 

(microns) 

Mean daily 

dentine lines 

(microns) 

Occ. Lat. Cv Axial Lat. 

Lengths 

from dentine 

horn to cr. 

completion 

(microns) 

Crown form. 

times 

estimated 

using dentine 

(years) 

Crown form. 

times using 

enamel from 

Table 2 

(years) 

Juvenile 

P. heseloni 

HT3/91A LR I1 30 1:1·98 25 5·0 1706 0·94 0·77+ 

HT3/91B LR I2 15 35 1:1·84 5·0 1643 0·90 0·81+ 

HT3/91D LR dm1 3·5 320 0·25 

HT3/91E LR dm2 22 1:1 occ 3·5 2·5 595 0·46 

HT3/91F m LR M1 12 21 45 1:1 occ 16·7 3·3 

HT3/91G m LR M2 14 35 1:1·59 15·0 2·4 1·3 1185 1·35 0·8+ 

Adult 

P. heseloni 

HT2/91A LR C 24 47 3·0 2·0 2·4+ 

HT2/91B LR P4 19 35 25 1:2·62 12·5 2·5 1·8 1531 1·7 1·9 

HT2/91C m LR M1 28 20 28 1:2 occ 

HT2/91C d LR M1 18 45 12·2 2·5 1·7 1096 1·2 1·2 

HT2/91D m LR M2 2·5 1·4 

HT2/91D d LR M2 20 36 48 10·3 1174 1·6 

HT2/91E m LR M3 30 34 48 1:2 2·1 1·5 1·6 

HT2/91E d LR M3 12 23 42 1259 1·7 

Adult 

P. nyanzae 

RU 1721 m RM1 16 21 70 2·75 1·8 1924 1·9 2·0 

RU 1721 d RM1 16 30 65 1:2·68 2146 2·1 1·8 

RU 1695 m RM2 15 25 70 1:2·84 2·75 2027 2·0 2·1 

RU 1695 d RM2 20 64 2259 2·25 2·0–2·5 

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 (μm). 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.


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 dm 2 of the infant, 

the M 1 , the P 4 and the M 2 of the adult 

specimen, it was possible to make each of


191 

Table 5 

Proconsul root extension rate data 

Tooth 

Angle I 

(degrees) 

Angle D 

(degrees) 

Daily rate (d) 

(μm/day) 

Extension rate 

(μm/day) 

dm2 112 4·5 2·9 34·8 

M1 (apical 1/3) 107 16 3·5 12·7 

105 8 2·0 14·3 

98 7 2·0 16·4 

M1 (apex) 105 10 3·2 18·1 

100 5·5 1·9 20·4 

P4 (cervix) 115 20 2·1 6·1 

126 16 1·8 6·1 

108 15 1·7 6·5 

112 15 1·8 6·8 

M2 (cervix) 91 14 1·6 6·4 

101 15 1·6 6·2 

M2 (apex) 115 7 3·3 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 M 2 and P 4 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 

M 2 and P 4 were on average 6·5 μm per day. In 

the apical third of the root they were on average 

14·5 μm per day and close to the apex 

21·5 μm per day. The completed root lengths 

for these teeth are not all known but are 

approximately 7 mm in the P 4 and 8 mm in 

the M 1 and M 2 . 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 dm 2 

is estimated at 35 μm per day. This is equivalent 

to 200 days for a tooth root of just under 

6 mm long. Deciduous teeth contain incremental 

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 μm 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 M 1 and dm 2 . 

The lower line ‘‘Death’’ runs through the last dentine formed beneath the tallest cusp in I 1 ,I 2 and M 2 (d). Accentuated lines in the I 1 and I 2 germs and 

M 1 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 M 2 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 M 1 is indicated by a dashed line. An accentuated line just above crown 

completion and close to the cervix of the adult M 1 corresponds with a line in the cusp of the M 2 and is shown just above the dashed line in M 2 . The same 

line can be seen in P 4 just above the dotted line that indicated crown completion in M 1 . Another accentuated line in the cervix of the M 2 (shown just 

below the dashed line in M 2 ) matches a line in the P 4 cervix. The dashed line which represents adult M 1 crown completion time was located in both the 

M 2 and P 4 by counting the number of striae beyond the first accentuated line in each tooth. M 3 cannot be sequenced with these teeth.


193 

Table 6 

Summary of crown completion times 

Using perikymata Using enamel Using dentine Maximum value of means 

Tooth type 

P. nyanzae P. heseloni P. nyanzae P. heseloni P. nyanzae P. heseloni P. nyanzae P. heseloni 

dm1 0·25 0·25 

dm2 0·46 0·46 

I1 2·5 2·4 2·5 2·4 

I2 2·5 2·4 2·5 2·4 

C 3·0–4·7 2·5 2·4 3·0–4·7 2·5 

P3 1·8 1·8 

P4 1·5 1·7 1·7 1·7 

M1 1·8 1·0 1·9 1·2 2·0 1·2 2·0 1·2 

M2 2·0 1·3 2·2 1·4 2·3 1·6 2·3 1·4 

M3 1·7 1·7 1·7 

Summary of data for crown formation times derived in three different ways in this study presented by tooth type. 

(i) Perikymata counts combined with cuspal enamel formation times derived from the histological sections of each 

tooth have been averaged for upper and lower teeth of the same tooth type. (ii) Estimates made from histological 

sections only when tooth crowns were complete. (iii) Estimates made from counts and measurements of 

incremental markings in dentine. In the last column the greatest values for crown formation times in both species 

of Proconsul are summarized. The estimates that appear here for P. heseloni were used in the bar chart of dental 

development (Figure 19). 

development in Proconsul. The first is the 

presence of both a strong and a fainter 

accentuated line that recur in the enamel of 

the P 4 and second M 2 of the adult P. heseloni 

specimen and the same strong line in the 

cervical enamel of the M 1 . These lines tie 

these teeth together developmentally. The 

second line of evidence comes from the 

accentuated lines in the incisor tooth germs 

and in the M 1 germ belonging to the infant 

P. heseloni individual. The third line of evidence 

comes from the distribution of linear 

hypoplastic bands on the buccal enamel 

surface of KNM-RU 7290. One strong band 

with two fainter bands either side of it, can 

be cross-matched across all the anterior 

teeth, across the premolars and across the 

M 2 s. The positions of these accentuated 

lines within the enamel and of the hypoplastic 

bands combined with the perikymata 

counts on the surface of the teeth of 

KNM-RU 7290 allow us to reconstruct a 

preliminary sequence of tooth development 

for P. heseloni from this specimen. The timing 

of the initial mineralization of the third 

molar is conjectural but we have simply 

presumed here that it follows the pattern 

and sequence known from histological 

studies on dental development for certain 

other primates where initial mineralization 

overlaps with M 2 crown formation (Beynon 

et al., 1991; Chandrasekera et al., 1993; 

Reid & Dirks, 1997; Reid et al., 1998; 

Swindler & Beynon, 1992) but this of course 

may turn out not to be so in Proconsul. 

Summary of the results 

The following ten key points summarize the 

results of this study. (i) Enamel thickness on 

the lingual aspect of the permanent lower 

incisor crowns in P. heseloni most resembles 

that in extant New World monkeys and 

hominoids and differs from that in extant 

cercopithecoids in that it is not absent or 

exceptionally thin. (ii) There is no evidence, 

from this study that P. heseloni or P. nyanzae 

had relatively thin molar enamel. The 

measure of ‘‘relative enamel thickness’’ for 

posterior teeth in P. heseloni and P. nyanzae 

falls above and beyond the range previously 

recorded for P. major and P. africanus,


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 μm 

per day. (iv) The pattern of a prolonged 

period of enamel formation in M 2 s 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 M 1 and M 2 of P. nyanzae were 

between 1·8 and 2·5 years. 

Discussion 


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 

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


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


Figure 16. Striae of Retzius in the cervical region of P. nyanzae and C. apella. InProconsul 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 Proconsul 

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 M 2 of C. apella 

with those in the M 2 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


197 

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 M 2 sinPan 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 

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 6μm 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 M 2 , for example, the mean value 

for the spacing of daily lines was 2·6 μm 

(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


Figure 17. Accentuated lines in the enamel and dentine of the P. heseloni adult M 1 (a) and a human M 1 

(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


199 

Figure 18. Regular accentuated lines in the dentine of the M 2 of P. nyanzae. Inthistooththeselonger 

period lines are spaced approximately 90 days apart and are of unknown aetiology. 

the M 2 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 M 2 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 M 2 might 

not be expected to have begun to mineralize 

until 10 months of age or so. This suggests 

the M 2 germ may have belonged to another 

infant that was just over two years old at 

death. 

It is also notable that the M 1 crown of this 

infant has no root preserved, but dentine is 

completely formed to the level of the enamel


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 M 1 indicates formation began 30 days before 

birth, (ii) the neonatal line in dm 2 indicates formation began 60 days before birth, (iii) root extension rates 

suggest the dm 2 root took 200 days to form, (iv) dentine formation times indicate I 2 formation began 12 

days after I 1 , (v) the absence of a neonatal line in dm 1 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 M 1 roots take longer to form than 

M 2 roots and that M 3 roots take the longest time to form, (viii) in this study we estimate 2·3 years for M 1 , 

2·7 years for M 2 and 3·0 years for M 3 root formation for P. heseloni. The overlap of M 3 with M 2 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 M 1 crown is also a little different in 

morphology to the other M 1 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


201 

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 M 1 and M 2 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 M 1 

and M 2 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). 

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


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 M 1 crown formation time in 

P. heseloni in this study are around 14 

months after birth (approximately 30 days of 

M 1 formation occurred before birth). If root 

extension occurred at the same rate as in M 2 

and P 4 at an average 6·4 μm per day (and 

poor data from one M 1 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 primates 

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 M 1 

and M 2 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


203 

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, 

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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Appendix 1 

Species 

Accession 

number 

Tooth 

type 

Tooth 

aspect 

Perikymata per mm of tooth crown height Sum of 

Cusp Cervix stria Years 

P. heseloni RU 7290 LLI1 B (12) 15 15 16 (17) (17) (19) (20) (20) (151) 2·07 

P. heseloni RU 7290 LLI1 B (12) (12) (12) 16 17 (17) (19) (20) (20) (145) 1·99 

P. heseloni RU 7290 ULI1 B (13) (14) (17) 17 (17) (19) (20) (20) (20) (157) 2·15 

P. heseloni RU 7290 URI1 B (13) (13) (14) (17) 17 17 (19) (20) (20) (20) (170) 2·33 

P. nyanzae FT 49 ULI1 B 6 6 7 8 10 11 12 13 11 (20) (104) 1·71 

P. nyanzae RU 1685 ULI1 B 3 7 9 9 11 12 16 14 16 13 (20) (20) (150) 2·46 

P. heseloni RU 7290 LLI2 B 8 11 13 14 17 18 19 20 (20) (140) 1·92 

P. heseloni RU 7290 LRI2 B (11) (13) (14) (17) 17 17 19 (20) (20) (20) (168) 2·30 

P. nyanzae RU 1716 LLI2 B 2 8 8 10 13 15 17 17 17 20 20 (20) (167) 2·75 

P. heseloni RU 7290 ULI2 B (9) (12) 17 17 17 16 (20) (108) 1·48 

P. heseloni FT 3637 URI2 B (9) (12) 17 14 12 (20) (20) (104) 1·71 

P. nyanzae RU 2031 URI2 B 2 12 14 14 18 21 21 (18) (120) 1·97 

P. heseloni RU 7290 LLC B 3 9 16 16 16 20 24 26 26 156 2·14 

P. heseloni RU 7290 LLC B 9 9 13 15 15 16 20 20 20 20 157 2·15 

P. nyanzae RU 1716 LLC B 8 8 10 12 12 12 15 16 18 18 16 16 161 2·65 

P. major SO 396 LRC B (12) (12) (12) (12) (13) 13 15 15 18 15 12 14 14 14 12 12 10 12 (12) (12) (261) 4·29 

P. heseloni RU 7290 ULC B (10) 13 15 16 17 17 17 17 (19) (19) (160) 2·19 

P. heseloni RU 7290 URC B (12) (15) 15 17 17 18 16 (19) (19) (148) 2·03 

P. heseloni RU 7290 LLP3 B 10 10 15 16 16 16 20 103 1·41 

P. heseloni RU 7290 LLP3 B 10 15 12 15 16 15 20 103 1·41 

P. heseloni RU 7290 LLP4 B 6 10 14 15 14 18 77 1·05 

P. heseloni RU 7290 LLP4 B 6 10 14 15 16 18 79 1·08 

P. heseloni RU 1733 ULP4 B 10 11 13 21 27 23 105 1·44 

P. heseloni RU 1733 ULP4 B 10 8 16 12 16 15 14 91 1·25 

P. heseloni RU 7290 LLM1 MB 6 10 13 16 45 0·62

Appendix 1 Continued 

Species 

Accession 

number 

Tooth 

type 

Tooth 

aspect 

Perikymata per mm of tooth crown height Sum of 

Cusp Cervix stria Years 

P. nyanzae RU 2087 LLM1 DB 6 11 13 16 46 0·75 

P. nyanzae RU 2087 LLM1 DL 6 10 14 16 46 0·75 

P. major SO 396 LLM1 MB 6 11 11 16 13 57 0·94 

P. heseloni RU 7290 LLM2 DL 2 8 12 16 24 62 0·85 

P. heseloni RU 7290 LLM2 DB 2 6 12 20 16 56 0·77 

P. nyanzae RU 2087 LLM2 MB 6 6 16 28 56 0·92 

P. nyanzae RU 2087 LLM2 ML 6 16 17 24 63 1·03 

P. nyanzae RU 2087 LLM2 DB (8) (13) 20 (23) (64) 1·05 

P. nyanzae RU 2087 LLM2 DL 6 6 10 14 22 27 85 1·40 

P. heseloni RU 1820 LLM3 MB 14 24 31 69 0·95 

P. heseloni RU 1931 LLM3 MB (20) 24 (24) (68) 0·93 

P. heseloni RU 7290 LLM3 MB 2 6 13 24 21 66 0·90 

P. heseloni RU 1820 LLM3 ML 16 24 24 20 (24) (108) 1·48 

P. heseloni RU 1931 LLM3 ML 14 20 24 58 0·79 

P. heseloni RU 1820 LLM3 DB 6 (14) 20 26 (66) 0·90 

P. heseloni RU 1931 LLM3 DB (20) (20) 20 (60) 0·82 

P. heseloni RU 1820 LLM3 DL 20 22 (24) (66) 0·90 

P. heseloni RU 1931 LLM3 DL 2 7 15 24 48 0·66 

P. major SO 396 LLM3 MB 6 6 13 17 16 20 78 1·28 

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.


209 

Appendix 2 

Species 

Accession 

number 

Tooth 

type 

Tooth 

aspect 

Total 

perikymata 

Lat. ena. 

form. 

(yrs) 

Cuspal 

form. 

(yrs) 

Crown 

form. 

(yrs) 

Mean cr. 

form 

(yrs) 

P. heseloni RU 7290 LL I1 B 151 2·07 0·22 2·29 

P. heseloni RU 7290 LR I1 B 145 1·99 0·22 2·21 2·25 

P. heseloni RU 7290 UL I1 B 157 2·15 0·33 2·48 

P. heseloni RU 7290 UR I1 B 170 2·33 0·33 2·66 2·57 

P. heseloni RU 7290 LL I2 B 140 1·92 0·33 2·25 

P. heseloni RU 7290 LR I2 B 168 2·30 0·33 2·63 2·44 

P. heseloni RU 7290 UL I2 B 108 1·48 0·33 1·81 

P. heseloni FT 3637 UR I2 B 104 1·42 0·33 1·75 1·78 

P. heseloni RU 7290 LL C B 156 2·14 0·42 2·56 

P. heseloni RU 7290 LR C B 157 2·15 0·42 2·57 2·57 

P. heseloni RU 7290 UL C B 160 2·19 0·42 2·61 

P. heseloni RU 7290 UR C B 148 2·03 0·42 2·45 2·53 

P. heseloni RU 7290 LL P3 B 103 1·41 0·42 1·83 

P. heseloni RU 7290 LL P3 B 103 1·41 0·42 1·83 1·83 

P. heseloni RU 1733 UL P4 B 105 1·44 0·42 1·86 

P. heseloni RU 1733 UL P4 B 91 1·25 0·42 1·67 1·77 

P. heseloni RU 7290 LL P4 B 77 1·05 0·42 1·47 

P. heseloni RU 7290 LL P4 B 79 1·08 0·42 1·50 1·28 

P. heseloni RU 7290 LL M1 MB 45 0·62 0·44 1·06 1·06 

P. heseloni RU 7290 LL M2 DL 62 0·85 0·50 1·35 

P. heseloni RU 7290 LL M2 DB 56 0·77 0·50 1·27 1·31 

P. heseloni RU 1820 LL M3 DB 66 0·90 0·78 1·68 

P. heseloni RU 1931 LL M3 DB 60 0·82 0·78 1·60 



P. heseloni RU 1820 LL M3 MB 69 0·95 0·78 1·73 

P. heseloni RU 1931 LL M3 MB 68 0·93 0·78 1·71 

P. heseloni RU 1820 LL M3 ML 108 1·48 0·78 2·26 

P. heseloni RU 1931 LL M3 ML 58 0·79 0·78 1·57 

P. heseloni RU 7290 LL M3 MB 61 0·84 0·78 1·62 1·68 

P. nyanzae RU 1716 LL C B 161 2·65 0·43 3·06 3·06 

P. nyanzae FT 49 UL I1 B 104 1·71 0·33 2·04 

P. nyanzae RU 1685 UL I1 B 150 2·47 0·33 2·8 2·42 

P. nyanzae RU 1716 LL I2 B 167 2·75 0·33 3·08 

P. nyanzae RU 2031 UR I2 B 120 1·97 0·33 2·3 2·69 

P. nyanzae RU 2087 LL M1 DB 46 0·76 0·9 1·66 

P. nyanzae RU 2087 LL M1 DL 46 0·76 0·9 1·66 

P. nyanzae RU 1721 U M1 B 65 1·07 0·9 1·97 1·76 

P. nyanzae RU 2087 LL M2 DB 64 1·05 0·93 1·98 

P. nyanzae RU 2087 LL M2 DL 85 1·40 0·93 2·33 

P. nyanzae RU 2087 LL M2 MB 56 0·92 0·93 1·85 

P. nyanzae RU 2087 LL M2 ML 63 1·03 0·93 1·96 2·03 

P. major SO 396 LR C B 261 4·29 0·42 4·71 4·71 

P. major SO 396 LL M1 MB 57 0·94 0·9 1·84 1·84 

P. major SO 396 LL M3 MB 78 1·28 0·93 2·2 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 M 1 and M 2 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.

Comparative dental development and microstructure of ... - UCL

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