Lawrence Martin Department of Anthropology, University College London, Gower Street, London WCIE 6BT, U.K.

Received 7 July 1980

Keywords : Proconsul, Koru, Songhor, Miocene, sexual dimorphism.

New Specimens of Proconsu l from Koru, Kenya

The morphological and metrical definitions of the three species of Proconsul: Proconsul africanus, Proconsul nyanzae and Proconsul major, are reviewed. New finds of large fossil primates from the Lower Miocene deposits at Koru, Kenya are described and assigned to two of these species; P. africanus and P. major. The large sample of P. major t:com Koru permits a more complete understanding of the morphology and variability of this species and necessitates a revised diagnosis. The increased range of variation ihr this species is discussed in the light of sexual dimorphism and species variability in extant African hominoids.

1. In troduct ion

Dr M. Pickford has worked at Koru since 1977 and expeditions under his direction have recovered large numbers of dental and gnathic remains. The large-bodied primate material is comprised mainly of isolated teeth but includes an associated maxillary postcanine dentition and a superb mandibular specimen. This collection considerably en- larges the sample of Proconsul major as well as providing the first associated upper dentition of this species and a female lower canine in association with a complete lower postcanine dentition. These specimens are described below and the enlarged range of variation resulting for this species is considered in the light of sexual dimorphism and population variability in living African apes and is shown to be similar to that seen in Gorilla gorilla.

Specimens from Koru have been assigned to three species of Proconsul by earlier workers. One specimen (Mt4086) has been attributed to each of the three species by different workers (Hopwood, 1933b; Le Gros Clark & Leakey, 1951; Pilbeam, 1969). Koru provided the first Miocene primates from Kenya and the historical treatment of specimens from this site has had considerable influence on the interpretation of material from other sites.

Hopwood (1933a) described two species of large hominoid from Koru, Proconsul africanus and Xenopithecus koruensis based on M14084 and M14081 respectively. Later Hopwood (1933b) added lower molars to P. africanus (including M14086), while recog- nizing that the maxillary material represented a smaller animal than did the mandibles. Specimens described by Le Gros Clark & Leakey (1950) demonstrated the presence of several species of different size, and the discovery of the P. africanus skull (M32363) in particular showed that the Holotype was in fact a large, probably male, example of the species. This invalidated MacInnes' (1943) interpretation of sexual dimorphism in this species as he had considered the Holotype to be female and the large Koru mandible, and M16647, to be males. Therefore these two specimens were removed to a new species P. nyanzae. In addition the new material from Songhor included specimens considerably larger than those assigned to P. nyanzae, and this material was designated a third species, P. major (Holotype M16648). The finds of small P. africanus specimens narrowed the metrical distinction between this species and X. koruensis and Le Gros Clark & Leakey (1951) considered these species to be synonymous, and they also predicted the later finds would tend to lessen the distinction between P. nyanzae and P. major.

Journal of Human Evolution (1981) 10, 139-150

0047-2484181/020139 + 14 $02.00/0 �9 1981 Academic Press Inc. (London) Limited

140 L. MARTIN

Material discovered at Moroto and Napak, in Uganda, was referred to P. major by Allbrook & Bishop (1963) on the basis of size, as no complete maxillary material is available from Songhor for comparison. Pilbeam (1969) suggested that, on the basis of the variation seen in the Ugandan sample, many of the P. nyanzae specimens from Songhor were in fact female P. major. He considered an edentulous mandible (KNM-SO 404) to represent a female P. major on the basis of its mandibular dimensions and morphology. Pilbeam also pointed out the morphological similarities of the Koru mandible (M14086) to KNM-SO 404. This interpretation reduced the metrical distinc- tion between the two species, but Pilbeam emphasized that P. nyanzae has relatively smaller anterior teeth in general and M1 in particular than P. major. Andrews (1978) assigned P. major and P. nyanzae a single morphological description due to their near morphological identity. The specimens were differentiated mainly on the basis of size and distribution but a number of morphological differences between the two species were discussed in the text.

Abbreviations used in this paper are as follows: K N M - K O , LG, CA, K Q , RU, SO; Kenya National Museum-Koru formation, Legetet formation, Chamtwara member, Kapurt ray formation (prior to 1977 specimens from these formations were all given the prefix, KNM-KO, regardless of their stratigraphic position), Rusinga Island, Songhor: UMP; Uganda Museum, Primate collection. The new material from Koru is described below with reference to the detailed descriptions in Andrews (1978), and differences, where they occur, are discussed in the text. All dimensions are listed in Tables 1-3.

2. Proconsul africanus H o p w o o d 1933a New material from Koru Nineteen specimens represent most of the upper permanent and part of the lower permanent dentition. No maxillary or mandibular specimens are known but one specimen represents an associated partial maxillary tooth row. Two deciduous canines are referred to this species.

Incisors. 11 (CA 1801), 12 (CA 1779) and I2 (LG 52) are preserved and resemble previously described P. africanus material.

Canines. Two upper (CA 1910, LG 921) and two lower canines (CA 586, CA 2149) are morphologically similar to P. africanus. CA 1910 is small, low-crowned and bilaterally compressed, LG 921 is a large and probably male example of this species.

Premolars. A single p3 (CA 1887) probably belongs to this species although the crown is relatively broad.

Upper molars. M 1 (CA 1872 and 1893, LG 902 and K Q 1) are similar to previously described specimens although CA 1872 lacks a protoconule and is somewhat larger than previously described specimens. M e (KO 95B, K O 100) show more wrinkled occlusal enamel, more rounded cusps and less well defined trigon than is usual in this species but probably belong to P. africanus on the basis of the associated M a. M 3 (KO 95A, CA 2250) is morphologically very reduced distally and is identical to previously described specimens of this species.

Plate 1. Female P. major mandibles, occlusal view. (a) LG 452; (b) SO 404.

140

Plate 2. Koru P. major jaws. (a) P. major female mandible (LG 452) lateral view; (b) P. major associated right maxillary dentition (CA 387-391); (c) P. major maxilla occlusal view (CA 1855); (d) P. major maxilla lateral view (CA 1855).

Table 1

KORU PROCONSUL

P. africanus dental dimensions (mm)

141

Mesio-distal Buccolingual Buccal Specimen n u m b e r length b read th height

Incisors C A 1801 (11 ) 7"2 5.8 7.0 C A 1779 (I s) 4.3 4.7 5.9 L G 52 (Is) 4"6 5"3 7.5 Canines C A 1910 (C 1) 8'8 6.8 9.8 (*) L G 921 (C 1) 10-6 8-7 16"7 C A 2149 (C1) 8"8 5.6 11.4 Premolars C A 1887 (p3) 5"7 10'5 8"7 Molars C A 1872 (M I) 8.9 9.6 - - C A 1893 (M 1) 7.7 8.9 - - L G 902 (M 1) 7.5 8.7 - - K Q 1 (M 1) 7.3 9.0 - - K O 95B (M s) 8"9 11"0 - - K O 100 (M 2) 8-9 10.7 - - K O 95A (M s) 8.0 11.5 - - C A 2250 (M 3) 8.4 9.9 - - C A 1771 (M1) 8.0 7.2 - - C A 1773 (M1) 8.5 7.8 - - L G 1389 (M3) 11-9 9.3 - - Deciduous teeth C A 608 (dO) 5"7 3-8 7.4 C A 2252 (dO) 5.0 4"2 5'4

Note: dimensions followed by (*) are best estimates.

Lower molars. M 1 (CA 1771 & 1773) both resemble P. africanus morphology although CA 1773 is slightlylarger than previously known specimens. M 3 (LG 1389) is morphologically like P. africanus, though the hypoconulid is vestigial and the tooth tapers markedly distally.

Deciduous canines, dO (CA 608 & 2252) is morphologically and metrically similar to previously described P. aJ~icanus specimens.

3. Proconsul major Le G r o s C l a r k & Leakey 1950 New material from Koru

Thirty-three specimens represent the complete permanent dentition and parts of the deciduous dentition. The material includes mainly isolated teeth but particularly important are a nearly complete mandible (LG 452) and an associated maxillary post- canine dentition (CA 387-391).

LG 452 (locality 14)

The complete mandibular body is preserved (Plates 1 and 2) with the root of the right ramus and the anterior portion of the root of the left ramus. The crowns of right C1-M3 and left P3-M3 and the crown base of the left C1 are preserved. The roots of the right and left Ii& 2 are also present. LG 1481 (I~) was found in the screening which produced this

142 L. MARTIN

specimen (in 47 pieces~ and Pickford (pers. comm.) believes it to be associated with the mandible. The body is very robust, especially in the region of the symphysis and below M2/~, and posterior to this it becomes more gracile. The body is deepest below the premolars and shallows posteriorly to the mandibular angle. The buccal surface of the mandible is swollen around the Pa root, inferior to which lies the mental foramen about 75% down the mandible. The inferior border of the mandible is bluntly rounded from the symphysis to below M~ where it tapers. The rami are broad based and the anterior edge forms an angle of 70 ~ with the tooth rows. They arise level with the distal M 2 and obscure all but the protocone of M 3. The retromolar angle is wide and well marked as is the submandibular fossa which is continuous with the sublingual fossa. No mylohyoid line is visible but the ridge of tile mandibular neck is present superior to the mandibular foramen and is quite wide. The anterior portion of the symphysis midline is an almost flat convex surface down to the level of the mental foramen and it then curves back sharply posteriorly to a point below C1/Pa where a ridge-like tubercle forms the most inferior point of the mandible. On the lingual aspect there is a shallow genial fossa above the tubercle, and superior to the genial fossa is the mental spine, which lies on the inferior surfhce of the superior transverse torus. The dental arcade is U shaped, but the tooth rows are very slightly convex so that M1-M I is the minimum breadth.

The mandible is very like M14086 and SO 404 in size and morphology. In particular, tooth row length and arcade shape are almost identical in LG 452 and SO 404. Mandibular symphysis cross sections are extremely similar in these forms (Bosler, pers. comm.).

Anterior dentition. The incisors are only preserved as root or alveolar outlines, and these are flattened ellipses in cross-section. The canine is low-crowned and the crown is strongly bilaterally compressed. A long deep and wide mesial groove runs from the unworn tip to a slightly elevated lingual cingulum, which forms a shelf-like inferior boundary to the groove. The prominent mesial ridge marks a hard angle between the buccal and lingual faces of the tooth. The distal face is flat with a slight buccaI, as well as distal, ridge. The tip is slightly blunted but no dentine is exposed, no other wear is visible. The tip is formed at a long junction of the mesial, distal and buccal ridges giving a blade like appearance to the tip which contrasts strongly with the pointed tip in P. nyanzae. Metrically this tooth is at the bottom of the P. nyanzae range. Its size and morphology strongly suggest that this is a female specimen of whatever species it represents. There is a slight diastema (about 2-2 ram) between C 1 and P3. The left P3 is more worn than its antimere, and the tooth is strongly bilaterally compressed with its long axis at 30 ~ to the tooth row. The cusp lies on the line of the buccal cusps of the molars and its tip is distally placed giving the crown a long mesio-buccal face. The mesial end of the buccal face has a highly polished facet inferiorly, running from the mesial ridge across the cingulum, and there is considerable enamel extension down the buccal root. Metrically this tooth falls in the upper end of the P. nyanzae range. P4 is slightly worn on the lingual cusps but the transverse ridge and the mesial ridges of the cusps are well marked. The latter meet a large mesial cingulum to define a large, but very mesio-lingually placed mesial fovea. The distal ridges are less well marked but combine with the large distal cingulum to complete a very large talonid. The cusps are approximately equal in height. This tooth is metrically at the top of the P. nyanzae range but is narrower at the same length than M14086.

I~ORU ekOCO~VSUL 143

Lower molars. M 1 is slightly worn with dentine exposed on the protoconid and hypoconid. The cusps are set centrally on the occlusal surthce. The trigonid is deep and clearly defined by strong ridges. The talonid is formed by the junctions of cusps rather than by ridges, except lingually. The talonid floor is thus restricted. The buccal cingulum is large and distally it becomes continuous with the hypoconulid, forming a platform lingual to the distal fovea. The metaconid shows an accessory cusp on its distal surface. This tooth is as large as the largest P. nyanzae but slightly smaller than other P. major specimens. M2 is much larger than M 1 (M~/M1 is 140%, considerably greater than the mean value for P. nyanzae or P. major) and the occlusal surface is more open as the cusps are more marginally placed. Morphology is otherwise as described for M 1 except that the hypo- conulid is isolated and the buccal cingulum is less massive than in M 1. This tooth falls at the upper end of the P. nyanzae range close to M14086 though it is smaller than other P. major. M 3 has the three buccal cusps forming a line and the tooth tapers distally, especially on the lingual side, as the entoconid is reduced and appears as one of a group of cuspules. The hypoconulid is also reduced and appears as a high point on the distal cingulum. Morphology is otherwise similar to MI/~ although there is no accessory cuspule on the metaconid and the hypoconid is so expanded that it divides the talonid into two areas. Metrically the tooth tMls centrally in the P. nyanzae range and is smaller than any known P. major.

On the basis of size LG 452 is either a large P. nyanzae or a small P. major if it belongs to an existing species. The canine in this specimen is of female morphology and falls well down the P. nyanzae range in size. All of the other teeth and the mandibular proportions, by contrast, fall at the top of the P. nyanzae range except for Ma. The morphology of M3 is rather different to that in P. nyanzae though it closely resembles the pattern seen in P. major. It seems improbable that a specimen with one of the smallest canines should have the largest and most robust mandible and postcanine dentition, so this specimen cannot be assigned to P. nyanzae. The similarity to the edentulous SO 404 mandible has been mentioned already and it seems probable that SO 404 is in fact a female example of P. major.

CA 387/391/390/388/389 (locality 34)

A set of right crowns (Plate 2) Pa-M 3, were found in association in a primary deposit. The teeth were found in contact (Pickford, pers. comm.) and the interproximal facets match perfectly. The wear on the teeth is in normal proportion and their morphology is compatible. This set of teeth can therefore be regarded as representing a single individual.

Premolars. The P~ is quite heavily worn so that both cusps are equal in height although the buccal cusp has more dentine exposed. There is no trace of a transverse ridge or of distal ridges but the mesial ridges are strongly marked. The crown outline is more rectangular than in other specimens of P. major but the morphology is otherwise similar. The length of the tooth can be matched in P. nyanzae but the breadth is considerably greater than any known P. nyanzae specimen. The p4 is worn as described for the p3 above. The occlusal area is circular in outline but the crown is given an ovoid cross-section by well developed buccal and lingual cingula. Morphology is otherwise as seen in previously described P. major specimens. The two species overlap in size in this tooth but CA 391 falls at the top of the P. nyanzae range.

1 4 4 L. MARTIN

Table 2 P. major j aw m e a s u r e m e n t s ( m m )

Mandible LG 452 Maxilla CA 38%391

Symphysis depth 40.4 Symphysis thickness 22'0 Body depth at P4 33.3 Body thickness at Pa 15.6 Body depth at M 2 29.5 Body thickness at M 2 18.9 M1-M8 length 35-3 P3-M3 length 54.0 C1-M3 length 66.7 I - I breadth 14-6 C-C breadth 19-6 PeP4 breadth 26-7 M3-M3 breadth 36-2

(*)

MI-M 8 length 34"2 P3-M8 length 49.8

Note: Dimensions are measured as defined in Andrews (1978), dimensions followed by (*) are best estimates.

Molars. The occlusal surface of M 1 is quite flattened by wear, with small areas of dentine exposed on all cusps especially the protocone. The morphology is similar to that in previously described specimens although the buccal cingulum is slight and the mesial and distal cingula have been incorporated into the occlusal surface by wear. The ranges for P. nyanzae and P. major overlap for M 1 but CA 390 would be a very large example of P. nyanzae as it is larger than the M 1 on the Holotype. M 2 is much larger than M 1 (M2/M 1 = 132 ~ ) and the lingual side of the tooth is considerably longer than the buccal side. The trigon ridges are weakly developed but the crista obliqua is well marked. The lingual cingulum is slight although the lingual root has a pronounced lingual flare. Metrically this tooth falls in the upper end of the P. nyanzae range although the range for P. major is poorly known. The M 3 is a rather square tooth but is rounded distally as the metacone and especially the hypocone are small in comparison with the mesial cusps. No crista obliqua is present but a line of cuspules appear in its place. The crown is circled by cingula except distally as this cingulum is greatly reduced. The morphology is otherwise as seen in previously described P. nyanzae specimens. Metrically the tooth falls in the upper end of the P. nyanzae range but it is morphologically rather different.

The morphology of M 3 and the size and morphology of the premolars group this specimen with P. major. There is some overlap with the upper end of the P. nyanzae range in the molars but morphologically and metrically these teeth are most like P. major.

CA 1855 (locality 34)

A left maxillary fragment with p3/4 and canine root (Plate 2). The maxilla is very robust with an inflated alveolus buccally, especially around p3 root. The long axis of the canine root is angled only slightly to the tooth row and the root outline is a wide oval. p3 is lightly worn b u t the buccal cusp is much larger than the lingual one. The morphology is otherwise as described for CA 387. Although CA 1855 is somewhat smaller than CA 387 it is considerably larger than any P. nyanzae yet known. P~ is morphologically identical with CA 391 although it is slightly smaller but still lies at the top of the P. nyanzae range.

KORU PROCONSUL 145

These premolars clearly represent the same taxon as CA 387 & 391, and closely resemble previously described P. major. The canine root in CA 1855 falls midway in the P. nyanzae range but, as was the case with the mandible, there is no reason to suppose that this specimen is a large P. nyanzae with a very small canine.

Isolated teeth

Upper incisors. 11 (CA 1300) and I s (CA 1858) are preserved. 11 resembles P. nyanzae in morphology and size although P. major is poorly known. I s is very like P. nyanzae specimens in morphology but it is too large for that species especially in bucco-lingual dimension. This specimen is larger than SO 554, previously described as P. major.

Upper canine. (CA 2127 & K O 103). The crown is rectangular in outline and is set diagonally in the tooth row. A slight buccal ridge marks the strong angle between the disto-buccal and mesio-buceal faces. A ridge runs across the crown tip from the mesial ridge to the distal ridge giving the tooth a blade-like cutting edge. The mesial groove is deep and long but otherwise the morphology is similar to that described by Andrews (1978). Metrically CA 2127 falls midway in the P. nyanzae range but close to CA 1855 which is associated with premolars too large for this species. In preserved parts KO 103 is identical to CA 2127 but it falls at the upper end of the P. nyanzae range.

Upper premolars. A heavily worn and damaged P~ (CA 607--comprised of the fragments CA 607 & 1802 which were found to join) probably belongs to this species on the basis of its length.

Upper molars. M 1 and M s (CA 568 and CA 392 and LG 924 respectively) are metrically and morphologically as described for CA 390 and 388 above. M a (CA 397, 1299, 1780) is morphologically as described for CA 389 above. The mesio-buccal root is larger than the disto-buccal root and the mesial portion of the lingual root is similarly larger than the distal portion reflecting the morphological reduction of this tooth. CA 1780 is larger than any known P. nyanzae but the other two specimens are of similar size to CA 389, falling towards the top of the P. nyanzae range.

Lower incisors. Two Ils (CA 1886 & LG 629) and one I s (LG 1481) are preserved. 11 is a high-crowned tooth with a rectangular cross-section at the base. Metrically these specimens fall towards the top of the P. nyanzae range but no P. major examples were previously known. I s is high-crowned with a flat buccal face and a distally sloping incisive edge. The possibility that LG 1481 is associated with the mandible LG 452 has already been mentioned. The root outline seen on the crown is quite different to that seen in the alveolus. To resolve these differences would require an additional portion of crown to be added to this already high-crowned tooth. This would have the effect of bringing the incisive edge level with the canine tip. While there may be some doubt as to whether this is the exact tooth belonging to the mandible, there can be little question that it represents the same species and can safely be used as a model.

Lower premolars. Two Pas (CA 1896 & 2251) and one P~ (KO 98) resemble these teeth in LG 452, though KO 98 is rather small which may be an artefact of damage.

1 4 6 L. MARTIN

T a b l e 3 P. major d e n t a l m e a s u r e m e n t s ( r a m )

Mesio-distal Buccolingual Buccal Specimen number length b read th height

Incisors CA 1300 (11 ) 8.4 CA 1858 (I s) 7'3 CA 1886 (11) 4.3 L G 629 (11) 6.0 LG 1481 (I,) 5.8 Canines CA 1855 (C 1) 12-4 CA 2127 (C 1) 12"1 K O 103 (C 1) 14-1 LG 452 (C1) 11.4 Premolars CA 387 (ps) 7"7 CA 607 (p3) 7.4 CA 1855 (W) 7.9 CA 391 (P~) 7-9 CA 1855 (p4) 7'3 CA 2251 (Pa) 11.3 LG 452 (Ps) 11.6 LG 452 (P4) 7.7 K O 98 (P4) 7-4 Molars CA 390 (M 1) 10.2 CA 568 (M 1) 10"5 CA 388 (M') 12"1 CA 392 (M 2) 12"2 LG 924 (M 2) 11"7 CA 3 8 9 ( M 3) 11"9 CA 397 (M '~) 10"2 CA 1229 (M 3) 10'8 CA 1780 (M '~) 14"3 CA 394 (M1) 10"6 CA 1856 (M1) 10'8 L G 452 (M1) 10'0 CA 395 (Ms) 12'8 CA 1298 (M~) 14"2 CA 2229 (M2) 11"3 LG 47 (Ms) 14"1 L G 452 (Ms) 11"7 LG 1390 (Ms) 12"2 LG 1472 (Ms) 12'4 CA 393 (M3) 13-8 LG 452 (M3) 13.2 Deciduous teeth LG 912 (dis) 4.1 M V 10 (dO) 7.9 CA 361 (dcl) 7.0 K O 97 (de1) 6-4 LG 48 (dps) 8.0 LG 1460 (dpa) 10'2

root)

(*)

7-0 8"3 6-3 5.7 5-6

10"6 10'2 10-6 8"2

12-1 10.7 11-8 12-3 11-3 7-0 7.0 7.8 7-3

(*)

(root)

(*)

(*)

12"2 11"8 13"5 13"3 13-4 13'6 13"3 13"3 16"2 9-4 9'4 9"2

11.2 (*) 13-2 10.8 12.9 11.0 11-0 10.4 11.5 11.1

4-2 6-8 5.8 5.0 5-8 8.0

10"6 9-8 7-8

12"9 (*) 8-8 (*)

15-7

14-9

7-1 (*) 5.o (*) 9"4 7-4 (*) 7"4

10"5 11-7

7-9 7"7 (*)

7.4 (*) 9"5 7'8 7.6 6-8

Note: dimensions followed by (*) are best estimates.

KORU PROCONSUL 147

Lower molars. M 1 (CA 394 & 1856) is of similar size and morphology to that described for LG 452 above, although the cusps are very rounded in CA 394. M 2 (CA 395, 1298, 2229, LG 47, 1390, 1472) is well represented in all stages of wear from an incompletely formed crown (CA 395 and L G 1472) to a completely flat crown. The unerupted teeth are rather narrow and have high cusps which wear down to give a square occlusal area which incorporates the cingula. The M2s are morphologically similar to previously described P. major specimens and to LG 452 and metrically vary from the top of the P. nyanzae range to the middle of the P. major range. M3 (CA 393) is slightly less morpho- logically reduced than are LG 452 and previously described P. major specimens but is otherwise similar. I t is slightly larger than LG 452.

Deciduous material. One di 2 (LG 912) probably belongs to this species. No comparable material is known but this tooth is larger than the permanent 12 ofP . africanus. One dO ( K N M - M V 10) is of similar size and morphology to previously described P. major specimens. Two d q are assigned to this species (CA 361 & K O 97) although no good comparable material is known. One dp8 (LG 48) is metrically similar to previously described P. major specimens. The dp4 (LG 1460) is morphologically identical to SO 542 (P. major) but is slightly larger.

4. Sexual Dimorphism and Variabil i ty in P. major

Much of the larger Koru material described above falls at the upper end of the P. nyanzae range or overlaps the lower end of the P. major range. I t is identified by Bosler (this volume) as a group (3) distinct from the P. major group at Songhor because only three isolated molars fall clearly into the P. major size range and only M 2 and M a show two distinct metrical clusters. Where morphological differences exist between P. major and P. nyanzae, however, the Koru material resembles P. major. Considering first the more complete specimens, the Koru mandible (LG 452) appears to be a female and is therefore unlikely to be a particularly large and robust P. nyanzae. Similarly the associated upper dentition is morphologically very like P. major. The premolars are considerably larger than any known P. nyanzae, and the molars fall at the top of the P. nyanzae range except for M a which is morphologically reduced as in P. major. All of the isolated teeth, except incisors, can be compared to these associated upper and lower dentitions and can be shown to accord well with their described morphology.

The morphological similarity and metrical overlap of the new Koru specimens with P. major lead to the conclusion that they are most similar to that species. Several possible interpretations of this similarity can be made. First the Koru material could represent a new species of Proconsul whose closest relative is P. major. Second it may be that the Koru forms represent a smaller geographical variant of P. major, or third that the Koru forms represent P. major as previously defined at Songhor.

In the case of the first interpretation a new species would be differentiated t?om P. major on the basis of size. Among the smallest of the Koru specimens (and of the entire P. major sample) in most teeth is the mandible (LG 452) which clearly represents a female. Several of the upper premolars as well as three isolated molars fall well within tile range of Songhor P. major. These specimens can either be seen as P. major tbund at the same localities as the new species or, as is more likely, male specimens which coexisted with females as represented by LG 452. The overall size range of the Koru sample

148 L. MARTIN

overlaps that of P. major from Songhor to such an extent that it cannot realistically be seen as a smaller geographical variant of that species. The existence of the small P. major mandible (SO 404) and the presence of small upper premolars (SO 527) at Songhor suggests that while sampling at Songhor has biased the P. major collection towards the large (?male) specimens, small (?female) examples are also present. The fact that two morphologically similar size groups may be found together in the same deposits at two sites supports the interpretation that they represent the males and the females of one species, P. major. The increased range of variation in P. major which results from this interpretation would have to be explained in terms of sexual dimorphism.

Pilbeam (1969) presents metrical data on chimpanzee and gorilla samples and their sexual variation. Garn et al. (1973) have demonstrated an index which quantifies sexual dimorphism in terms of the percentage by which male dimensions exceed female dimensions. Calculations based on this data are presented in Table 4.

In all of the postcanine teeth the SO 396/LG 452 dimorphism considerably exceeds the dimorphism seen between an average male and an average female gorilla, but is less than the maximum dimorphism for Pan (except in M3) and is considerably less than the maximum dimorphism for Gorilla. When the largest and the smallest Kenyan P. major are used as male and female the dimorphism is equal to or slightly greater than the Pan maximum but is well within the Gorilla maximum. This rather simple analysis shows that, when population variability is considered in addition to sexual dimorphism, the enlarged P. major sarnple shows total variation (for the presently known sample) slightly greater than that seen in Pan but less than that seen in Gorilla. Therefore it seems most reasonable to conclude that the large and small specimens found at Koru, and at Songhor, represent the males and females of one species which shows sexual dimorphism and population variability comparable with that seen in the extant African apes. The Koru material is therefore assigned to P. major.

5. A R e v i s e d D i a g n o s i s o f P. major

A species of Proconsul showing considerable sexual dimorphism and population variability. Large specimens approximate the female gorilla in dental size, small specimens approxi- mate the chimpanzee. The largest species of Proconsul, but showing considerable metrical overlap with P. nyanzae, particularly in the anterior dentition. Length of P3-Ma ranges from 50 mm to over 65 mm. Compared to tooth size the mandibular body is more robust than in P. nyanzae. M 3 typically larger and longer compared to M 2 and distal morphology is reduced. M s larger than M 1, the M1 larger than the M1 ofP . nyanzae. Canines with blade-like tip rather than the sharp point seen in P. nyanzae. Canines overlapping the entire P. nyanzae size range but extending considerably beyond this range. Incisors overlap P. ~yanzae in size and morphology but are very high-crowned and large examples considerably exceed the largest known P. nyanzae (emended from Andrews, 1978, p. 100).

6. T h e Ident i f i ca t ion o f P. ntajor in U g a n d a

The new sample of P. major from Koru considerably extends the known range of variation of this species. It also provides an associated maxillary postcanine dentition which can be reliably assigned to this species. The weight of evidence supports the conclusion that many of the specimens represent females of P. major and they serve to reinforce Pilbeam's (1969) identification of other female examples of this species (e.g. M14086, SO 404,

Tab

le 4

T

he

per

cen

tage

by

wh

ich

ma

le d

imen

sio

ns

exce

ed f

ema

le d

imen

sio

ns

in l

ivin

g an

d f

ossi

l A

fric

an h

om

ino

ids

Ca

P3

P4

M1

M2

Ma

L

B

L

B

MD

B

L

MD

B

L

MD

B

L

MD

B

L

Gor

illa

m

ale

mea

n/fe

mal

e m

ean

•

100

mal

e m

axim

um

/fem

ale

min

imu

m

• 10

0 P

an mal

e m

ean

/fem

ale

mea

n •

10

0 m

ale

max

imu

m/f

emal

e m

inim

um

•

100

P.

maj

or

SO

396

/LG

452

•

100

Max

imu

m/m

inim

um

•

100

Spe

cim

ens

used

abo

ve (

Max

imu

m/m

inim

um

)

39.2

36

,9

17.4

16

-3

8,3

7.2

5.4

5.5

6.8

7.6

10.0

7.

7 89

.2

79,8

49

.6

71.4

37

.5

42.7

25

.0

29.5

34

,5

41.2

43

.8

43.7

18.0

19

.1

--0.

9 8.

0 4,

0 2.

3 1.

9 2-

1 1.

8 2-

9 3.

0 2.

0 60

.6

57,5

19

.4

46.2

33

.3

28.2

27

.7

17.4

29

.6

34.8

30

,1

27-2

23"7

38

'3

--

--

15"6

24

.4

17"0

16

"3

14"5

18

'2

31'1

27

"9

23-7

38

.3

43"4

37

'1

22"1

32

"1

24"0

17

'4

28"8

36

'2

31'1

27

"9

SO

39

6/L

G4

52

S

O4

65

/CA

22

51

S

O4

16

/LG

45

2

SO

91

7/L

G4

52

S

O4

15

/M1

40

86

S

O3

96

/LG

45

2

Not

es:

Th

e ta

ble

show

s th

e se

xual

dim

orp

his

m s

een

betw

een

an a

vera

ge d

imen

sion

for

the

mal

e sa

mpl

e (G

oril

la =

20

, P

an =

13

or 1

4) a

nd

the

ave

rage

dim

ensi

on f

or t

he f

emal

e sa

mpl

e (G

oril

la =

20

, C

I =

18,

Pan

--

12,

C1

--

11).

In

add

itio

n P

ilbe

ams

(196

9) 9

5% c

onfi

denc

e li

mit

s ar

e us

ed t

o ca

lcul

ate

the

dim

orp

his

m w

hich

wou

ld b

e se

en i

f th

e la

rges

t m

ale

and

the

sm

alle

st

fem

ale

dim

ensi

ons

expe

cted

wer

e co

mpa

red.

T

wo

set

s of

dim

orp

his

m p

erce

ntag

es a

re s

how

n fo

r P

. m

ajor

. T

he

firs

t co

mpa

res

the

SO

396

man

dib

le (

prob

ably

mal

e) w

ith

the

LG

452

man

dib

le (

prob

ably

fem

ale)

. T

he

seco

nd s

et c

ompa

res

the

larg

est

(the

refo

re p

roba

bly

mal

e) w

ith

the

smal

lest

(th

eref

ore

prob

ably

fem

ale)

spe

cim

en i

n th

e pr

esen

tly

know

n K

eny

an P

. m

ajor

sa

mpl

e (t

his

is t

he c

lose

st a

ppro

xim

atio

n to

P.

maj

or m

ale

max

imu

m/f

emal

e m

inim

um

pos

sibl

e).

150 L. MARTIN

SO 527). The palate_from Moroto, Uganda considered by several authors to be P. major (Allbrook & Bishop, 1963; Bishop, 1964; Pilbeam, 1969; Andrews, 1978) differs from the expanded Kenyan sample in several important respects. Upper incisors, canines and premolars from Moroto are considerably larger, in general, than those of the Kenyan P. major sample. M 1/~ are of similar size in the two samples but M s is very much larger in the Moroto specimen. The large size of the anterior teeth in relation to the molars may well reflect a different dietary habit to that of the Kenyan P. major. On the basis o f the morphology of the Koru sample the Moroto material can no longer be considered to belong to this species. The Napak material cannot at present be differentiated from P. major, but its taxonomic status will remain uncertain until associated anterior and posterior dental material is recovered.

I am deeply grateful to Dr Martin Pickford for permission to study the collections which he has made at Koru since 1977, and to the Museum Trustees of Kenya for permission to study the material in their care. I am grateful to Drs P. Andrews and M. Pickford, and to T. Harrison for their helpful advise and discussions, and especially to Dr P. Andrews for his comments on the manuscript. The research was carried out with per- mission from the Office of the President in Kenya and was supported by grants from the Medical Research Council, London and the Boise Fund, Oxford.

References

Allbrook, D. & Bishop, W. W. (1963). New fossil hominoid material from Uganda. Nature 197, 1187-1190. Andrews, P.J . (1978). A revision of the Miocene Hominoidea of East Africa. Bulletin of the British ~Iuseum

of Natural History (Geology) 30, 85-224. Bishop, W. W. (1964). More fossil Primates and othez Miocene Mammals tYom north-east Uganda. Nature

203, 1327-1331. ,Garn, S. M., Lewis, A. B., Swindler, D. R. & Kerewsky, R. S. (1967). Genetic control of sexual dimorphism

in tooth size. Journal of Dental Research 46 (5) Supplement, 963-973. Hopwood, A. T. (1933a). Miocene Primates from British East Africa. Annals and Magazine of Natural History

series 10 11, 96-98. Hopwood, A. T. (1933b). Miocene Primates from Kenya. Journal of the Linnean Society (Zoology) London 38,

437-464. Le Gros Clark, W. E. & Leakey, L. S. B. (1950). Diagnoses of East African Miocene Hominoidea. Quarterly

Journal of the Geological Society London 105, 260-262. Le Gros Clark, W. E. & Leakey, L. S. B. (1951). The Miocene Hominoldea of East Africa. Fossil Mammals"

of Africa 1, 1-117. London: British Museum (Natural History). MacInnes, D. G. (1943). Notes on the East African Miocene Primates. ,lournal of the East African and Uganda

Natural tIistory Society 17, 141-181. Pilbeam, D. R. (1969). Tertiary Pongidae of East Africa: Evolutionary relationships and taxonomy. Peabody

Museum Bulletin 31, 1-185.