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New hominoid facial skeleton from the Early Miocene of Rusinga Island, Kenya, and its bearing on the relationship between Proconsul nyanzae and Proconsul africanus
Mark F. Teaford K. Christopher Beard Department of Cell Biologll and Anatomy, The Johns Hopkins University School of Medicine, Baltimore, MD 21205, U.S.A.
Richard
E. Leakey
National Museums of Kenya, P.O. Box 406.58, Nairobi, Kenya
Alan Walker Department of Cell Biology and Anatomy, The Johns Hopkinr Universi~ School of Medicine, Baltimore, MD 21205, U.S.A.
New hominoid facial skeleton from the Early Miocene of Rusinga Island, Kenya, and its bearing on the r&&ionship between Proconsul nyanzae and PRWOIISU/sfricanus Recent paleontological fieldwork has led to the discovery of a palate and partial face of a young adult male Proconsul on Rusinga Island, Kenya. Morphologically, it is most similar to Proconsul nyanzae. However, it is intermediate in size between Proconsul nyonzae and Proconsul a&anus. Since the distinction between these two species, not to mention the relationship between Procon& from Rusinga and other sites, is not as clear as it once was, this specimen will undoubtedly add further fuel to the fire ofdiscussions and debates concerning early Miocene hominoid taxonomy. In particular, it shows that we have relied far too heavily on limited samples of crania-dental material in making our taxonomic assignments and distinctions.
Received 14 July 1987 Revision received 12 April 1988 and accepted 25 April 1988 Publication
date September
1988
Keywords: Proconsul, Miocene, hominoid, maxilla, taxonomy
Journal of Human Evolution (1988) 17, 461-477
Introduction Rusinga Island, Kenya has long been known as one of the world’s best sources of Miocene primate fossils (Andrews, 1981). Still, the number of expeditions that have conducted systematic surveys of the sites on Rusinga has been surprisingly small. Over the past four years, the National Museums of Kenya and Johns Hopkins University have jointly conducted annual paleontological expeditions on Rusinga. The primary goal of these and (if necessary) expeditions has been the systematic survey, surface collection, Thus far, results have been extremely excavation of Miocene sites on Rusinga. encouraging, and a variety of primate material has been recovered, both from surface collections of material missed by previous investigators and excavations of newly exposed material (Beard et al., 1986; Walker et al., 1986). During the 1985 field season, the palate and partial face of a young adult male Proconsul was recovered at site R107. It rivals the holotype of Proconsul nyanzae, BM(NH) Ml6647 (LeGros Clark & Leakey, 1951; MacInnes, 1943; Whybrow & Andrews, 1978), in terms of its completeness. However, it is intermediate in size between specimens assigned to P. afiicanus.and P. nyanzae, the two species of Proconsul traditionally considered to occur at Rusinga. Since the distinction between these two species continues to be a topic of discussion and debate within the paleontological literature (e.g., Andrews, 1978; Bosler, 1981; Greenlield, 1972, 1980; Kelley, 1986; Kelley & Pilbeam, 1986; Pickford, 1986; Pilbeam, 1986), and the taxonomic relationship between Rusinga Proconsul and Proconsul from other sites (e.g., Koru) is not as clear as it once was (Kelley, 1986; Martin, 1981; Pickford, 1986), this new specimen (KNM-RU 16000) will play a critical role in interpretations of Early Miocene hominoid taxonomy. 0047-2484/88/050461
+ 17 $03.0010
0
1988 Academic
Press Limited
462
M. F. TEAFORD
ET AL.
Geological setting
The specimen was discovered by Wambua Mangao on the south side of the valley forming the boundary between sites RI06 and R107 (Pickford, 1984). Pieces of the specimen were scattered over an area of approximately 20 square feet. Nearly all material was recovered through surface collecting, although a few fragments were recovered from subsequent sieving of the soil and loose surface debris. In any case, all pieces came from surface wash and none was found in situ. The hillside on which the specimen was found is part of a large exposure of the Rusinga Agglomerate (Van Couvering, 1972). However, the grey-green matrix adhering to the specimen was not exposed on the hillside. Instead, patches of the matrix were found on top of the hill just above the Agglomerate. Since a major path crosses the top of the hill, the specimen was probably knocked down the slope (in one or several large pieces) by passing humans, cattle, or goats.
Materials and methods Overall, the specimen is beautifully preserved (see Figure 1). The only obvious distortion is due to (1) buckling and crushing of the left interorbital region; (2) slight, superior displacement of the right posterior portion of the palate in the vicinity of the greater of the left zygomatic (by 2-4 mm) along palatine foramen; and (3) d ownward displacement Otherwise, the specimen preserves much of the the zygomaticomaxillary suture. premaxilla and maxilla, all of the postcanine dentition except the crown of RPs, and most of the left zygomatic including half of the inferior orbital margin. Four fragments from the nasal/interorbital region are fastened together but cannot be attached to the rest of the specimen. Dental, palatal, and facial measurements were taken with a set of Fowler “Max-Cal” digital calipers. Measurements were generally the same as those described by Andrews (1978) and Pilbeam (1969). Any exceptions are noted in the text. To insure comparability of measurements, previously published measurements of Proconsul material were checked on original specimens in the National Museum of Kenya. Measurements that had to be estimated for the new material are noted by brackets in Tables 1 and 2. Comparisons are East African material preserving palatofacial made with previously-described morphology. However, in light of possible differences between Proconsul africanus from the Tinderet sites (such as Koru and Songhor) and specimens referred to Proconsul africanus from the Kisingiri/Rangwa sites (Rusinga and Mfangano) (Kelley, 1986; Pickford, 1986)) dental measurements for specimens from the two areas are presented separately in tables and figures. Specimen abbreviations are as follows: Kenya National Museum-KNM-RU (Rusinga), KNM-MW (Mfangano), KNM-SO (Songhor), KNM-KO (Koru formation), KNM-LG (Legetet formation), KNM-CA (Chamtwara member); KNM-KQ (Kapurtray formation); BM(NH)-British Museum (Natural History); UM-P-Uganda Museum, Primate Collection.
Palatofacial morphology The alveolar bone of the premaxilla is slightly eroded between the incisor alveoli. However, the border between the right and left central incisor alveoli is preserved well enough to yield an estimate of naso-alveolar height. That estimate (9.3 mm) is relatively low, even for Proconsul (see Table 1). Still, the incisors were probably no less procumbent than in other
HOMINOID
FACE FROM RUSINGA
ISLAND,
463
KENYA
Proconsul specimens as evidenced by the slope of the naso-alveolar clivus (approximately 40” to the tooth row) and the orientation of the incisor alveoli within the premaxilla. The alveolar border between the right canine socket and the right lateral incisor is also well-preserved with a sizeable diastema (6.5 mm) (see Figure Id), larger than that of any specimen referred to P. africanus (Andrews, 1978) and well within the range observed b) Andrews (1978) for P. n_yanZaeand P. major. Table 1
Palato-facial Measurements (comparative measurements Andrews 1978; Pilbeam 1969; Whybrow and Andrews 1978) KNM-RU 16000 Naso-alveolar height Naso-alv. hr./M’-M’s Nasal aperture height Nasal aperture breadth Nasal apert. br./ht. Zygomatic arch height Maxillary Maxillary Maxillary Palate Palate Palate (br. at (br. at Depth Depth
sinus length sinus breadth sinus br./ I.
length breadth at canine breadth at M? C)/(br. at M2) M*)/length at C/P’ at My
Inter-orbital breadth Inter-orb./Xasal ap.br. Inter-orb./Pal.br. at M’ Inter-orb./C-Mjlength Ml-M3 length Ps-Ms length C-M3 length * Measurements restoration [] = estimates
16.0
F9.31 [31,2%]
[G] 20.0 64.5% 17+*
1321 22.8 [71.3%]
I I.2
11.1 41.5% 19.6 14-o 71.5% 7.1
l6.i 45.5% [361 30.2 84.0% 14.0 46.0 I 7.0 37.0%
__ 45.0 19.0 23.6 80.5% 524% 5.1 6.8
79.0 37.0 33.4 110.8% 43.6% 4.0 7.5
24.8 124.0% 85.3% 41.0%
18.0 128.6% 76.3% 40.5%
20.0 66.2% 6 I .6% 27.1%
33,2* 46.8* 60.5
25.8 365 44.4
66.0* 29.8 29. I 102.3% 48.5% * 7.0* 8.5
[27,4]
[ 120,2%]
Andrews
UM-P 62-1 I
Il.2
58.6 28.6 28.4 100.7% 48.5% 5.1 7.3
[96,5% [50,8%]
KNM-RU 7290
_
133.4) 13.8 41.3%
29.8 41.6 53.9 from
BM(NH) Ml6647
from
1
11978) on BM(NH)
36.7 54.6 73.7 Ml6647
befre
Posteriorly, the premaxilla and maxilla form an incisive foramen like that in other P~ocon.wl specimens (Ward & Kimbel, 1983; Ward & Pilbeam, 1983). The subnasal alveolar process of the premaxilla ends well-anterior to the front edge of the palatine processes of the maxillae leaving a large incisive foramen (maximum diameter 9.4 mm) and effectively no incisive canal (see Figures 1c and Id). As in the Moroto palate (UM-P 62- 11) originally attributed to P. major (Allbrook & Bishop, 1963),1 broad, shallow grooves run anteriorly from the incisive foramen along the inferior surface of the subnasal alveolar process on either side of the midline. Superiorly, the nasal processes of the premaxilla extend up the lateral walls of the nasal aperture. As in the 1948 skull of P. afticanus (KNM-RU 7290)) the premaxillary-maxillary 1Since the taxonomic assignment ofthis specimen to P. major has been disputed in the literature (Leakey, 1963; Martin, 1981), it will merely be referred to as either the Moroto palate or specimen UM-P 62-11 in this paper.
464 Table 2
M. F. TEAFORD
ET AL.
Dental measurements (Pan measurements taken from Pilbeam, 1969; Proconsul measurements taken from Andrews, 1978, incorporating changes/additions described by Kelley, 1986; Martin, 1981; Pickford, 1986)
Species (sites)(ilr)
Mean MD Length (mm) (2 S.D.)
Mean BL Breadth (mm) (+
SD.)
Canine P. africanus (Tinderet) (5) P. ajkicanus (Rangwa) (9) KNM-RU 16000 P. tzyanzae ( 10) Pan (males) (14) Pan (females) (11)
10.7 f 1.1
8.1 + 0.7
9.2 + 0.5
7.2 ?C0.5
14.5 13.2 f 1.1 14.0 + 1.2 11.3kO.5
11.7 10.5 _+ 0.9 10.9 f 1.3 8.9 + 0.3
PJ P. africanus (Tinderet) (2) P. africanus
6.5 + 1.3
8.6 f 1.1
5.9 f 0.3
9.0 + 0.7
(Rwzwa) (3) KNM-RU 16000 P. nzantae (5) Pan (males) (13) Pan (females) (11)
6.7 7.3 + 0.5 8.1 f 0.6 7.9 + 0.4
I@2 10.8 k 0.4 10.5 f 0.5 10.5 f 0.6
P4 P. africanus (Tinderet) (2) P. ajicanus (Rang+ (6) KNM-RU 16000 P. nyanzae(11) Pan (males) (13) Pan (females) (11)
5.7zk0.1
9.3 + 0.4
5.4f 0.4
9.1 + 0.7 104 10.7 1; 0.7 10.2 + 0.4 10.2 f 0.3
6.1 6.6 f 0.6 7.0 + 0.3 7.0 + 0.3
M' P. africanus (Tinderet) (7) P. africanus (Rangwa) (IO) KNM-RU 16000 P. nyancae(8) Pan (males) (12) Pan (females) (11)
7.7+ 0.6
9.0 f 0.4
7.8+ 0.5
9.2 + 0.6 10.0 10.6 f 0.7 11.2f0.5 11.2+@6
8.5 8.9 f 0.3 9.9 f 0.5 98 + 0.5
M4 P. aficanus (Tinderet) (5) P. afiicanus (Rangwa) (11) KNM-RU 16000 P. nyanzac(5) Pan (males) (13) Pan (females) (11)
8.9+ 0.5
ll.OkP5
8.4f 0.7
IO.1 AZ0.9 11.7 12.2 + 1.1 11.7+@5 11.4 ?r 0.7
10.6 10.9 f 1.1 10.2 f 0.7 10.0 f 0.6 MS
P. ajicanus (Tenderet) (4) P. africanus (Raw-) (4) KNM-RU 16000 P. nyanzae(8) Pan (males) (11) Pan (females) (9)
8.2 + 0.3
IO.8 + 0.8
8.2 + 0.5
10.6 f 0.5
10.5 11.1 + 1.1 9.2 f 0.6 9.0 + 0.6
12.2 13.3 f 1.1 11.0 + 1.0 10.9 f 0.6
HOMINOID
FACE
FROM
RUSINGA
ISLAND,
KENYA
465
sutures are clearly visible in anterior view showing that the nasal processes of the premaxilla formed most of the lateral wall of the nasal aperture. The aperture itself is wider than that of the holotype of P. nyanzae (see Table l), but probably not as high, although with the buckling of the left interorbital region the latter measurement is difficult to estimate. Ir any case, the aperture is significantly larger than the only one available for P. u.anus (KNM-RU 7290). The base of the aperture resembles the broad, gutter-like base of the Moroto palate (Pilbeam, 1969) rather than the narrow, seam-like base noted by LeGros Clark and Leakey (1951) for P. africanus (KNM-RU 7290). Probably the most striking features of the face of this specimen are the pronounced canine juga dominating the anterior part of the maxillae (see Figures 1b and 1d). While the inferolateral wall of each canine socket is broken away, the maxillae still show marked concavities posterior to each canine jugum. The premaxillae also show slight concavities anterior to each canine jugum, and in this respect, KNM-RU 16000 differs slightly from the restored holotype of P. nyunzue which exhibits a more convex surface in this area. As Ward & Pilbeam (1983) have noted, many factors can influence the development of canine fossae. In the case of KNM-RU 16000, it should be noted that the canines were probably implanted in a similar fashion to those of the restored holotype of P. nyunzue-i.e., with roots tilted slightly towards the midline and almost no external rotation (see Figures la and Id). Thus, the concavities anterior to the canine juga may reflect a slightly more procumbent premaxillary region. The remainder of the alveolar processes of the maxillae are intact except for a tiny fragment distal to RMs. The palate is larger than that of specimens attributed to P. africanus (BM[NH] M14084, KNM-RU 7290) but not quite as large as that of the restored holotype of P. nyanzae (see Table 1). It narrows slightly at the level of P4, but overall the tooth rows are essentially parallel. The ratio of palate breadth at the canines to palate breadth at M* is 10@7’~~, which is noticeably different from Andrews’ (1978) estimates for the 1948 skull of P. africanus and is closest to that for the restored holotype of P. nyanZae (Whybrow & Andrews, 1978) (see Table 1). The depth of the palate is similar to that for other Proconsul specimens which are, in turn, much shallower than those of modern great apes (Pilbeam, 1969). Most ofthe sutures of the palate are still visible (see Figure Id), although the premaxillae were originally broken from the maxillae along much of the premaxillary-maxillary suture in this specimen. The intermaxillary suture is visible in its entirety. The greater palatine foramen lies opposite the mesial part of Ms and, on the left side, the maxillopalatal suture is clearly visible moving anteriorly from the foramen to a point opposite mid-M* before turning abruptly towards the midline. The anterior part of the right maxillopalatal suture is visible, but most of the right palatine is missing. Most of the interpalatine suture is preserved. Large portions of the medial and lateral walls of the maxillary sinuses are missing in KNM-RU 16000. In addition, the floor of the right maxillary sinus has not been cleaned of matrix. Still, the floor of the left maxillary sinus and extensions of the sinus into the root of the left zygoma allow a better appreciation of the form and extent of the sinus than has been possible before. In fact, the superolateral corner of the sinus is also visible near the inferolateral margin of the orbit. This reaffirms Pilbeam’s (1969) observations on the extent:of the maxillary sinus based on isolated fragments associated with the Moroto palate. The floor of the maxillary sinus extends from the distal edge of P4 into the maxillary tuberosities (as visible on the small portion of tuberosity on the right side). At its
466
M. F. TEAFORD
ET AI.
Figure 1. New Proconsul specimen (KX.M-RU 16000) from Rusinga Island, Kenya: a (top left), anterior view; b (bottom left), left lateral view; c (top right). superior vie\\,. d (bottom rqht), inferior view.
468
ET AL.
M. F. TEAFORD
anterior-most point, the floor of the sinus lies well above the roots of P4 and Mr. It then ridge over the slopes down to a slight excavation above M*; it rises in a transverse mesiobuccal root of M3; and then descends into another shallower excavation above Ms. The alveolar bone over the distobuccal roots of both Ms’s projects into the sinus. The floor of the maxillary sinus of the new specimen is thus slightly more irregular than that of certain Proconsul specimens (e.g., KNM-RU 2036), but it still does not approach the degree of convolution of other specimens (e.g., KNM-RU 1677A), and it certainly is not multilocular as in modern great apes (Pilbeam, 1969). The root of the zygoma arises above M* (see Figure Id). As Andrews (1978) has noted, this is the usual condition in P. nyaneae and modern great apes, but it contrasts with that in P. africanus. As mentioned above, the zygomatic bone is displaced downward slightly along the zygomaticomaxillary suture; as a result, its orbital process is probably twisted slightly posteriorly. Still, the face must have been set at an angle of 50-60” to the plane of the teeth (as estimated from a line running along the anterior surface of the orbit and a line between the center of the crowns of Ps and Ml) (see Figure 1b), and this value is similar to estimates from the restored holotype of P. nyanzae (Whybrow & Andrews, 1978) and the Moroto palate (Pilbeam, 1969). Th e inferior margin of the zygomatic is roughened and slightly excavated for the origin of the superficial masseter. Precise measurements of the interorbital region are extremely difficult due to the crushing and buckling on the left side and the fact that the four nasal/interorbital pieces cannot be firmly attached to the rest of the face. Nonetheless, the most inferior part of the anterior lacrimal crest is preserved on the left side, and the most superior part ofthe crest is preserved on the right side together with portions of inter-nasal suture. Thus, an estimate ofinterorbital breadth can be made by measuring the distance from the crest to the midline on the right side and doubling that figure (see Table 1). This is roughly comparable with the measurements provided by Pilbeam ( 1969) and Whybrow & Andrews ( 1978), although their measurements were probably taken inferior to the one used here. The main point is that the interorbital breadth of KNM-RU 16000 is probably larger than that of the restored holotype of P. nyanzue, and it is certainly larger than that of the 1948 skull of P. africanus (KNM-RU 7290)*. These differences are even more striking when considered in light of the relatively small palate and tooth rows of KNM-RU 16000. For instance, the ratio of the interorbital breadth to the internal palate breadth at M2 is much larger than that for the holotype of P. nyanzae (see Table 1)
Dentition Since the anterior teeth are missing from this specimen, the bulk of this description will concentrate on the postcanine teeth. However, given the importance of canine size differences in interpretations of primate morphological variability, a few words must be said about canine size in KNM-RU 16000. Canines
Measurements of the maximum length of each canine alveolus and estimates of the left canine alveolus show that the canines ofthis specimen were not only larger than those of any Rusinga specimen of P. ajicanus, they were also larger any specimen of P. nyanzae except the holotype (see Figure 2a). This is despite 2 The interorbital breadth of KNM-RU new values are presented in Table 1.
7290 was increased
in a recent reconstruction
of the width significantly than those of the fact that
(Walker ct al., 1983). The
HOMINOID
FACE FROM RUSINGA
ISLAND,
KENYA
469
KNM-RU 16000 has a relatively small palate and its postcanine teeth are intermediate in size between P. a&anus and P. nyanzae (see below). Given the relative size of its canines, this individual must certainly have been a male. Premolars
The crown of RPs is broken-off near the cervical margin, and it was never recovered in sieving at site R107. However, the crown of LPs is in excellent condition, showing only a slight degree of wear and a small dentin exposure on the tip of the paracone. Morphologically, the Ps of KNM-RU 16000 is most similar to those assigned to P. nyanzae, although it lies at the low end of the size range for that species (see Figure 2b). As in all Proconsul specimens, the paracone is taller than the protocone, but that difference is not as marked as in most specimens of P. africanus and P. nyaneae. The paracone is also not as slender and projecting as in the holotype of P. africanus from Koru (BM[NH] M14084). The mesial and distal crests of the paracone are well-developed, with small tubercles at their mesial and distal ends, respectively. However, the mesiobuccal flange is not as pronounced as in some specimens of P. nyanzae and P. major. The mesial and distal crests of the protocone are nearly absent, but small wear facets suggest that some form of shearing was still occurring along these edges. A slight transverse ridge connects the protocone and paracone and it separates a tiny, vertical,, mesial fovea from a larger distal fovea. The enamel of the distal fovea is slightly ,wrinkled, leaving three faint ridges running distolingually from the paracone into the fovea. The enamel of RP4 is eroded or etched, but most morphological features are still visible on it. The LP4 is in excellent condition, with no dentin exposures but a moderate degree of faceting on the distal protocone. In terms of standard length and width measurements, the P4 of KNM-RU 16000 is intermediate in size between those assigned to P. afticanus and P. nyaneae (see Figure 2~). Morphologically, P4 is fairly similar to Ps, thus only the differences will be mentioned here. As in other Proconsul specimens, the difference in height between the paracone and protocone on P4 is not as pronounced as that on Ps. This is due to a relative decrease in height of the paracone rather than a relative increase in protocone height. P4 has a more rounded, oblong appear’ance in occlusal view a8 compared with Ps in which the mesiobuccal flange gives the crown a more angular appeaiance and makes the mesial portion of Ps larger than that of Ph. The transverse ridge betweed the protocone and paracone of P4 is split by a groove running mesiodistally from the distal fovea. This, in conjunction with a slight wrinkling of the distal portion of the occlusal surface, leaves the transverse ridge of P4 less pronounced than that on Ps. Finally, the lingual cingulum on P4 is more developed than that on Ps, although it is not as distinct as those on the molars. Molars
As with the premolars, the molars on the left side of this specimen are generally i? much better condition than those on the right side. Specifically, RMl and the mesial half of RM2 are eroded and etched so that only the basic morphological features are discernible. The remainder of the right and left molar series is lightly etched in places but, overall, the teeth are in excellent condition. Ml has dentin exposures on all its cusp tips except for the hypocone. M* shows very little wear-just the slightest faceting along its occlusal ridges. Ms is not quite into occlusion although its buccal cusp tips show evidence of occasional tooth-food-tooth contacts. Ml is by far the smallest of the molars, lying at the upper end of the size range for specimens assigned to P. africanus (see Figures Id and 2d). Its cusps are essentially equal in
470
ET AL.
M. F. TEAFORD
Maxillary
14
canine
size in Proconsul and Pun
(a)
XX
12 -
l x l '4 ‘g x m
.
__
I
:: P.africanus-T P.africanus-R P.nvanzae &males &females KNM-RU 16000
..X@ .x . .
X
‘8*
0
61 8
l
x
X IO -
e
I
I
I
Maxillary
I
I
1
P3 size in Proconsul
12
ond Pun
.
(b)
X' b
3 0
Maxillarv
x
l l .
x
x,
__ a .
x
.
l
g 8
x x
xx
:
P4 size in Proconsul
and Pun
II
IO
5
7
6 Meslodistol
length
(mm.1
I II6
14
12
IO
47 Maxillary
MI size in Proconsul
and Pan
12, l*
- (d)
..
xxI
xx .
ox’
II -
P
x
lxx
II Maxillary M2 size in Proconsul
-
and fan
(e)
13 -
X .
x
x.
Er+ p El* Q
x ox*
x*
0
. .
7
8
IO
9
Maxillary
M3 size In Proconsul
and Pun
I6
X
I
8 7
I 8
I
I
I
9 Mesiodistol
II
I
IO
II
length
I,I
I I2
13
(mm.)
Figure 2. Scatterplots of mesiodistal length vs. buccolingual breadth for the maxillary teeth of KNM-RU 16000 and a comparative sample of Proconsul specimens and males and females of Pan frogfodylcs. Comparative specimens are the same as those in Table 2 which are taken from Andrews (1978), Martin (1981), and Pilbeam (1969). P. aficantcs-T = P. aficanur specimens from the Tinderet sites (SO, KO, LG, CA, KQ); P. ajicanur-R = specimens traditionally referred to P. aficanw from the Rangwa sites (RU and MW). a, Maxillary Canines; b, Ps; c, P4; d, Ml; e, M*; f, Ms.
472
M. F. TEAFORD
ET AL.
size although the metacone is noticeably taller than the other cusps. The trigon is not as well-defined as in P. u@xnus. However, the talon is probably better developed than in either P. africanus or P. nyunrue. Correlated with this is the fact that there is a large distal fovea on Mr and the hypocone is not isolated from the trigon as in many specimens of P. uficanus and P. nyunzue. As in other Procond specimens, the mesial fovea is bounded by two ridges running from the protoconule, to the paracone and the mesial edge of the tooth. However, the fovea and ridges are extremely small and the protoconule has essentially been obliterated by wear. The ridges along the buccal edge of the tooth are well-developed, but the intersection of the ridges joining the paracone and metacone is relatively high above the central basin as in P. nyunzue rather than deep within a buccal groove as described by Andrews (1978) for P. ufticunus. The lingual cingulum is fairly welldeveloped-running from the protoconule to the lingual side of the hypocone. As in other specimens of P. ujicunus and P. nyunzue, the distal cingulum blends into the talon while the buccal cingulum is reduced to a tiny shelf between the paracone and metacone. M* is certainly larger than Ml, but it is nearly equaled in size by Ms. It lies at the low end of the size range for P. nyunzue (see Figure 2e), and the ratio of M* and Ml size is closer to that for P. nyuneue than to that for P. ufricunus (see Table 3). Since the lingual side of the tooth is longer than the buccal side, M* has more of a rhomboid shape than Mr (see Figure Id). This is probably due to the fact that the protocone and protoconule are relatively large, and the hypocone and distal cingulum combine to extend the distolingual margin of the tooth slightly. Still, that distolingual bulge is not as marked as on certain specimens of P. major (e.g, KNM-CA 388, Martin, 1981). The occlusal ridges on the buccal side of M* are well-developed. However, the lingual boundaries of the trigon are relatively poorly-defined because thep are interrupted by the protoconule, metaconule, and the longitudinal sulcus. As on M*, two faint ridges from the protoconule outline a tiny mesial fovea. However, the hypocone retains a slight ridge to the protocone, but that ridge is split by a lingual groove that runs into the large distal fovea. The lingual cingulum is fairly large, showing moderate beading around the protocone and the mesial portion of the hypocone. Ms has a very small hypocone. However, a massive protocone and large lingual cingulum contribute to an overall occlusal area (mesiodistal length X buccolingual breadth) that is nearly identical to that of M*. Needless to say, the Ms of KNM-RU 16000 is certainly not the “greatly reduced” tooth that has traditionally been cited as a characteristic feature of P. ufn’cunus (Andrews, 1978). Nevertheless, it is still small by P. nyunaze standards (see Figure 2f). The small hypocone is barely recognizable, yet the paracone and metacone are ofreasonable size. Coupled with the massive protocone, the net result is a tooth that is dominated by the trigon and is nearly triangular in occlusal outline. The ridges that define the lingual boundaries of the trigon, however, are barely discernible since they are broken into segments by a prominent protoconule and metaconule. The mesial fovea is still quite small and the distal fovea is obstructed by small cuspules. The lingual cingulum is larger than that on M2 and is prominently beaded. Due to the small size of the hypocone, the lingual cingulum may appear to be larger than it actually is, since it forms a prominent border around the lingual side of the tooth.
Discussion With improvements in the fossil record, investigators are sometimes forced to deal with specimens that fall between established taxonomic categories. These intermediate forms
473
HOMINOID FACE FROM RUSINGA ISLAND, KENYA
not only give us a better understanding of morphological variation in extinct species, they occasionally force us to question some of the criteria used to make taxonomic distinctions. KNM-RU 16000 is such a specimen. Within the current taxonomic framework for Early Miocene hominoids, three alternative interpretations of this specimen are possible. I. KNM-RU 16000 as a male Proconsulnyanxae To some investigators, the question of what to do with this specimen will be an easy one. Nearly all of the traits traditionally used to distinguish Proconsul afficanus from Proconsul nyanzae indicate that KNM-RU 16000 is a Proconsul nyanpae. These include canine size, the relative sizes of the upper molars, relative development of occlusal ridges on the upper molars, Ps shape, palate shape, location of the root of the zygoma, and shape of the nasal aperture, (Andrews, 1978; LeGros Clark & Leakey, 1951; Whybrow & Andrews, 1978). This pattern of similarities also extends to most of the ratios of tooth size that have been used in analyses of Proconsul material and modern primate material (see Table 3). In fact, the only trait for which this specimen presents a problem is postcanine tooth size. Thus, while the palate is only slightly smaller than that of the restored holotype of Proconsul dentition is clearly intermediate in size between Proconsul nyaneae, the postcanine
Table 3
Ratios and sums of maxillary dental measurements for Proconsul and Pan. As in Table 2, measurements are taken from Andrews (1978) md Pilbeam (1969). Ratios and rums are the same aa those used by Greenfield (1972), Lucas et al. (1986), and Pickford (1986)
P. ajiicanus BM(NH) 14084* KNM-RU 1705 KNM-RU 1904 KNM-RU 1973 KNM-RU 2036 KNM-RU 7290 Mean k S.D. (all P. ufic.) (P. afic. from Rusinga) KNM-RU
16000
P. nyanzac BM(NH) 16647 KNM-RU 1674 KNM-RU 1677 KNM-RU 2088 Mean f S.D. Pan troglodytes males (range) females (range) Mean f S.D. males females * Type specimen
Canine area: M 1 area
P4 area: Ml area
M 1area: M3 area
Ml length: ML?length
Postcanine tooth area (P3-M3)
123.3 103.2
67.7 65.4
91.4 _ _ _ _
85.9
315.4 _ _ 377.6
265.9 264.3 + 1.6
Molar area (Ml-M3)
262.7 _
54.5 68.8
80.2
96.1 89.9 96.3 84.8
112.Ok8.4
64.1 f 5.7
85.8 + 5.6
90.6 + 4.9
3465 * 3.1
106.4 + 3.2
62.9 + 6.1
_
91.8 k 4.8
_
199.6
74.6
66.4
80.2
468.8
337.1
162.7 142.9 132.8 146.1 + 12.4
72.8 79.0 71.8 62.6 71.6 f 6.8
68.8 68.0 64.2 77.2 69.6 f 4.7
75.4 84.9 78.3 87.8 81.6 + 5.0
593.0 467.4 591.9 550.8 + 59.0
427.6 327.6 431.3 297.3 371.0 + 60.4
118 - 172.3 79 - 104.8
58.7 - 71.6 52.3 - 73.1
87.3 - 135.3 89.6 - 121.8
85.6 - 109.7 91.6 - 108.3
451.9 - 529.1 431.4 - 526.9
300.3 - 367 292.7 - 358.5
97.4 f 6.4 98.8 + 4.8
487.6 + 26.2 475.1 f 31.3
332.7 zk 23.3 318.7 + 24.3
109.6
147.3 zk 17.1 91.6+ 8.1
6.57 f 3.5 64.8 + 5.2
109.1 + 15.4 11@9f 11.3
of P. ajicanus from Koru; all other Proconsul specimens
_
in this table are from Rusinga
474
M. F.
TEAFORD
ETAL.
nyanzae and Proconsul africanus. Again,
that may not pose problems for some investigators, because KNM-RU 16000 could simply be a small Proconsul nyanzae. Yet, KNM-RU 16000 was presumably a male, and its canines were probably larger than those of any known specimen ofProconsul nyanzae except the holotype. It would be unusual for such a specimen to have among the smallest postcanine teeth in its species (e.g., see ratio of canine area: Ml area in Table 3). Finally, if this specimen were to be assigned to P. nyanzae, it would still leave us with a male-dominated P. nyanlae sample and a female-dominated P. africanus sample from Rusinga (Bosler, 198 1).
2. KNM-RU 16000 as a male of the small species of Proconsuljom Rusinga Another alternative would be to say that KNM-RU 16000 is not a Proconsul nyanzae but instead the first male specimen of the smaller species of Proconsul from Rusinga-i.e., that traditionally viewed as Proconsul africanus. This interpretation would avoid some of the problems inherent in assigning the specimen to Proconsul nyantae. For instance, the relative size of the canines might be used as a distinctive characteristic of males of such a species. However, this interpretation would also create some problems. Most notably, it would ignore all of the morphological criteria that have traditionally been used to make the distinction between Proconsul nyantae and Proconsul africanus, and it would do so without providing an alternative set of criteria for distinguishing between these species. Needless to say, it would certainly reinforce the idea that the small species of Proconsul from Rusinga is not Proconsul aficanus (Kelley, 1986; Pickford, 1986)) since the holotype of that species (from Koru) is also a male. Finally, it would still leave us with the important question raised by Bosler (1981): given the excellent Miocene hominoid fossil collections from Rusinga, why has it taken so long to find a male of this species? 3. KNM-RU
16000 as a male Proconsul
nyanzae
as de3ned by Kelley and by Pickford (Kelley,
1986; Kelley & Pilbeam, 1986; Pickford, 1986)
A new approach to this problem would be to say that although KNM-RU 16000 is definitely a Proconsul nyaneae, investigators have, until recently, been defining Proconsul nyanzae too narrowly. In other words, as both Kelley and Pickford (Kelley, 1986; Kelley & Pilbeam, 1986; Pickford, 1986) have suggested, perhaps we have underestimated the range of variation in this species, and all of the Proconsul specimens from Rusinga are Proconsul nyanzae, while Proconsul aficanus is found only at sites such as Koru and Songhor. From such a perspective, KNM-RU 16000 would merely be a small male Proconsul nyanzae albeit with large canines, while the females of that species would be the specimens from Rusinga traditionally referred to Proconsul ajicanw. As Kelley and Pickford admit, as far as dental metrics are concerned, this interpretation might require a greater degree of sexual dimorphism than that exhibited by modern baboons and gorillas. Furthermore, preliminary analyses of newly-discovered Proconsul material from Rusinga show that the dentition may be even less variable than the postcrania as far as size differences are concerned. For instance, initial analyses of the new wrist material (Beard et al., 1986) s h ow little more than size differences between specimens attributed to P. nyanzae and P. aficanus. However, those size differences range from 1.5 : 1 to 2 : 1 (for linear dimensions) depending on which bones are examined. Such size differences would be greater than those between males and females in modern hominoids, where ratios of 1.3 : 1 are generally the maximum (McHenry, 1986). M oreover, estimates of body weight
HOMINOID FACE FROM RUSINGA ISLAND, KENYA
475
based on allometric relationships with long bone cross-sectional dimensions (Ruff, in press) yield estimates of 9.6 kg for P. a&cams and 3 7 kg for P. nyanzae (based on analyses of two individuals per species). This reaffirms Walker & Pickford’s (1983) estimates of a 4 : 1 difference in body weight between these species (cf. Kelley, 1986; Pickford, 1986). Such body-size dimorphism within a single species is unprecedented in modern land mammals. Since body size itself is an important determinant of degree ofdimorphism (Leutenegger & Cheverud, 1985), such sexual dimorphism in a primate of this size would seem highly unlikely. For instance, published weights for Papio (Jungers, 1985; Leutenegger & Cheverud, 1982) yield estimates of body size dimorphism averaging less than 2: 1. As a correlate of such body size dimorphism, we would be left with a new, composite species made up of small females with relatively large teeth and very large males with relatively small teeth, Once again, Kelley and Pickford’s model would require that we revise our criteria for distinguishing between Proconsul nyanzae and Proconsul a&anus, as the traditional criteria would most effectively distinguish Rusinga males from Rusinga females within the same species. Summary
and conclusion
Given the problems with the alternative interpretations of KNM-RU 16000, perhaps the time has come to accept the fact that something is wrong with the criteria that have traditionally been used to distinguish between these species (see Kelley, 1986; Pickford, 1986 for reviews of this topic). A stable taxonomy for Proconsul will need larger samples and more associated material, and it should not overemphasize dental traits. Ontogenetically variable traits such as maxillary sinus morphology (Ward & Brown, 1986; Ward & Pilbeam, 1983) will have to be evaluated differently. KNM-RU 16000 includes a palate and partial face together with most of the maxillary dentition, yet its relatively large canines and relatively small posterior teeth make it an unusual specimen that is hard to assign to a known species. For the time being, this problem is best viewed in light of recent discoveries ofpostcranial material from Rusinga (Beard et al., 1986; Walker et al., 1985). As noted above, size differences in the new postcranial material indicate that there are two speciesof Proconsul on Rusinga. If we accept that assessment, then we can at least use the more complete craniodental material’(such as KNM-RU 16000) to produce a sample of males and females of each species on Rusinga. From this perspective, the most reasonable conclusion would be to view KNM-RU 16000 as a male of the smaller species of Rusinga Proconsul, although, clearly, such as assignment should be viewed with a great deal of caution. Analyses of new postcranial material from Rusinga may lead to the discovery of important differences between Proconsul species in functional complexes other than the jaws and teeth. Even if no functional differences are discovered, perhaps size differences will be of critical importance, for, as far as skeletal morphology is concerned, some modern species differ in little more than size (e.g., within the genus Cercopithecus). In any case, KNM-RU 16000 will play a pivotal role in future discussions of Proconsul taxonomy. Its unique combination of features has re-emphasized the view that we must look at all the evidence provided by cranial andpostcranial material, and we must not overlook our only modern primate analogues. Acknowledgments We thank the Government Governors of the National
of Kenya for permission to carry out research in Kenya and the Museums of Kenya. We thank Bw. Kamoya Kimeu and his
476
M. F. TEAFORD
ET
AL.
team for invaluable help in the field and at the National Museum in Nairobi. Many colleagues helped in various ways, but special thanks go to Peter Andrews, Bobbie Brown, Eric Delson, Dick Hay, Bill Jungers, Jay Kelley, Meave Leakey, Lawrence Martin, Emma Mbua, Mike Rose, Chris Ruff, Blaire Van Valkenburgh, and Steve Ward for help, useful discussions, and/or comments on the manuscript. We also wish to thank three anonymous reviewers for their helpful comments on the manuscript. This work was supported by the National Museums of Kenya and NSF Grant BNS 8418567. A. W. was also supported by a John Simon Guggenheim Memorial Fellowship during portions of this study.
References Allbrook, D. & Bishop, W. W. (1963). New fossil hominoid material from Uganda. Nature 197, 1187-l 190. Andrews, P. J. (1978). A revision of the Miocene Hominoidea of East Africa. Bull. Brit. Mus. (Nat. Hist.) Geol. 30, 85-224. Andrews, P. J. (1981). A short history of Miocene field paleontology in western Kenya. J. hum. Evol. 10, 3-9. Beard, K. C., Teaford, M. F. & Walker, A. (1986). New wrist bones of Proconsul aficanus and P. nyanzae from Rusinga Island, Kenya. Folia primatol. 47, 97-l 18. Bosler, W. (1981). Species groupings of Early Miocene dryopithecine teeth from East Africa. J. hum. Evol. 10, 151-158. Greenfield, L. 0. (1972). Sexual dimorphism in Dryo~ithecus ajicanus. Primates 1.3,395410. Greenfield, L. 0. (1980). A late divergence hypothesis. Am. J. phys. Anthrop. 5.2, 351-366. Jungers, W. L. (1985). Body size and scaling of limb proportions in primates. In (W. L. Jungers, Ed.) Size and Scaling in Primate Biology, pp. 345-381. New York: Plenum Press. Kelley, J. (1986). Species recognition and sexual dimorphism in Proconsul and Rangwapithccus. J. hum Evol. 15, 461-495. Kelley, J. & Pilbeam, D. R. (1986). The dryopithecines: taxonomy, comparative anatomy, and phylogeny of Miocene large hominoids. In (D. R. Swindler&J. Erwin, Eds) Comparative Primate Biology, Volume I: Systematicr, Evolution, and Anatomy, pp. 361-411. New York: Alan R. Liss. Leakey, L. S. B. (1963). East African fossil Hominoidea and the classilication within this super-family. In (S. L. Washburn, Ed.) Classification and Human Evolution, pp. 32-49. Chicago: Aldine. LeGros Clark, W. E. & Leakey, L. S. B. (1951). The Miocene Hominoidea ofEast Africa. Brit. Mus. (Nat. Hist.) Fossil Mammals of Africa, No. I. 117pp. in primates: ecological and size Leutenegger, W. & Cheverud, J. (1982). C orrelates of sexual dimorphism variables. Int. J. Primatol. 3, 387-402. Leutenegger, W. & Cheverud, J. M. (1985). Sexual dimorphism in primates: the effects ofsize. In (W. L. Jungers, Ed.) Size and Scaling in Primate Biology, pp. 33-50. New York: Plenum Press. Lucas, P. W., Corlett, R. T. & Luke, D. A. (1986). Sexual dimorphism of tooth size in anthropoids. In (M. Pickford & B. Chiarelli, Eds.) Sexual Dimorphism in Living and Fossil Primates, pp. 23-39. Firenze: 11 Sedicesimo. MacInnes, D. G. (1943). Notes on the East African Miocene primates. J. East Af 63 Uganda Nat. Hist. Sot. 17, 141-181. Martin, L. (1981). New specimens of Proconsul from Koru, Kenya. J, hum. Euol. 10, 139-150. McHenry, H. M. (1986). Size variation in the postcranium of Australopithecus afarensis and extant species of Hominoidea. Human Evol. 1, 149-156. Pickford, M. (1984). Guzcttccr of the Geology of Rusinga Island, prepared for the National Museums of Kenya. Pickford, M. (1986). Sexual dimorphism in Proconsul. In (M. Pickford & B. Chiarelli, Eds.) Sexual Dimorphism in Living and Fossil Primates, pp. 133170. Firenze: II Sedicesimo. Pilbeam, D. R. (1969). Tertiary Pongidae of East Africa: Evolutionary relationships and taxonomy. Peabody Mus. Nat. Hist. Bull. 81, 185 pp. Pilbeam, D. R. (1986). Hominoid evolution and hominoid origins. Am. Anthropol. 88, 295-312. Ruff, C. B. (1987). Structural allometry ofthe femur and tibia in Hominoidea and Macaca. Foliaprimatof. 48,9-49. Ruff, C. B. (in press). Body mass and lower limb bone cross-sectional dimensions and articular surface areas in anthropoid primates. In (J. Damuth & B. J, McFadden, Eds) Body Size in Mammalian Pateobiology. Cambridge: Cambridge University Press. Van Couvering, J, A. (1972). Geology ofRusinga Island and correlation of the Kenya Mid-Tertiary fauna. Ph.D. Dissertation, University of Cambridge. Walker, A., Falk, D., Smith, R. & Pickford, M. (1983). The skull ofProconsul afkanus: reconstruction and cranial capacity. Natarc 305, 525-527. Walker, A. & Pickford, M. (1983). New postcranial fossils of Proconsul ajicanus and Proconsul nyan.zac. In (R. L. Ciochon & R. S. Corruccini, Eds) New Interpretations ofApe and Human Ancestry, pp. 325-352. New York: Plenum Press.
HOMINOID
FACE FROM RUSINGA
ISLAND,
KENYA
477
Walker. A., Teaford, M. F. & Leakey. R. E. (1985). New Proronrul fossils from the Early Miocene ofKenya. .-lm.J. phy. Anthrop. 66, 239-240. M’alker, A., Teaford. M. F. & Leakey, R. E. (1986). New information concerning the R114 Proconsul site, Rusinga Island, Kenya. In CJ. Else and P. Lee! Eds) Proceedings ofthe .Yth Congress ofthe International Primatological So&@, I’olume 1: Pnmate Evolution, pp. 143-149. Cambridge: Cambridge University Press. Ward, S. C. & Brown, B. (1986). The facial skrleton of.Sioapithecus indicus. In (I). R. Swindler &J. Erwin. Eds) Lhmparntir~e Primate Biology. ~‘olume1: ~~yctemnticc. Erolufum. and Anntom_~.pp. 413-452. New York: Alan R. Liss. IYard. S. C. & Kimbel, W. H. (1983). Subnasal alveolar morphology and the ytcmatic position oE.Sir~apltheru\. .,lm. j. p&s. .4nthrop. 61, 157-171, \Vard, S. C. & Pilbeam. D. R. (1983). Maxillofacial morph&g) oE Miocene hominoids from Africa and Indo-Pakistan. In (R. L. Ciochun & R. S. Corruccini. Edsi AVeu~ Infer~re~ionc sf.Spc and Human .+lnce.ct~v. pp. 21 I-~238. New York: Plenum Prrss. bt’hybrow, P.,J. & :\ndrews. I’. 119781. Rrstoration ofthc holotype ot~Procunru/ nwzn:ae. I;olia ,6rimato~. 30, I1 5-l 25.
Richard
E. Leakey
National Museums of Kenya, P.O. Box 406.58, Nairobi, Kenya
Alan Walker Department of Cell Biology and Anatomy, The Johns Hopkinr Universi~ School of Medicine, Baltimore, MD 21205, U.S.A.
New hominoid facial skeleton from the Early Miocene of Rusinga Island, Kenya, and its bearing on the r&&ionship between Proconsul nyanzae and PRWOIISU/sfricanus Recent paleontological fieldwork has led to the discovery of a palate and partial face of a young adult male Proconsul on Rusinga Island, Kenya. Morphologically, it is most similar to Proconsul nyanzae. However, it is intermediate in size between Proconsul nyonzae and Proconsul a&anus. Since the distinction between these two species, not to mention the relationship between Procon& from Rusinga and other sites, is not as clear as it once was, this specimen will undoubtedly add further fuel to the fire ofdiscussions and debates concerning early Miocene hominoid taxonomy. In particular, it shows that we have relied far too heavily on limited samples of crania-dental material in making our taxonomic assignments and distinctions.
Received 14 July 1987 Revision received 12 April 1988 and accepted 25 April 1988 Publication
date September
1988
Keywords: Proconsul, Miocene, hominoid, maxilla, taxonomy
Journal of Human Evolution (1988) 17, 461-477
Introduction Rusinga Island, Kenya has long been known as one of the world’s best sources of Miocene primate fossils (Andrews, 1981). Still, the number of expeditions that have conducted systematic surveys of the sites on Rusinga has been surprisingly small. Over the past four years, the National Museums of Kenya and Johns Hopkins University have jointly conducted annual paleontological expeditions on Rusinga. The primary goal of these and (if necessary) expeditions has been the systematic survey, surface collection, Thus far, results have been extremely excavation of Miocene sites on Rusinga. encouraging, and a variety of primate material has been recovered, both from surface collections of material missed by previous investigators and excavations of newly exposed material (Beard et al., 1986; Walker et al., 1986). During the 1985 field season, the palate and partial face of a young adult male Proconsul was recovered at site R107. It rivals the holotype of Proconsul nyanzae, BM(NH) Ml6647 (LeGros Clark & Leakey, 1951; MacInnes, 1943; Whybrow & Andrews, 1978), in terms of its completeness. However, it is intermediate in size between specimens assigned to P. afiicanus.and P. nyanzae, the two species of Proconsul traditionally considered to occur at Rusinga. Since the distinction between these two species continues to be a topic of discussion and debate within the paleontological literature (e.g., Andrews, 1978; Bosler, 1981; Greenlield, 1972, 1980; Kelley, 1986; Kelley & Pilbeam, 1986; Pickford, 1986; Pilbeam, 1986), and the taxonomic relationship between Rusinga Proconsul and Proconsul from other sites (e.g., Koru) is not as clear as it once was (Kelley, 1986; Martin, 1981; Pickford, 1986), this new specimen (KNM-RU 16000) will play a critical role in interpretations of Early Miocene hominoid taxonomy. 0047-2484/88/050461
+ 17 $03.0010
0
1988 Academic
Press Limited
462
M. F. TEAFORD
ET AL.
Geological setting
The specimen was discovered by Wambua Mangao on the south side of the valley forming the boundary between sites RI06 and R107 (Pickford, 1984). Pieces of the specimen were scattered over an area of approximately 20 square feet. Nearly all material was recovered through surface collecting, although a few fragments were recovered from subsequent sieving of the soil and loose surface debris. In any case, all pieces came from surface wash and none was found in situ. The hillside on which the specimen was found is part of a large exposure of the Rusinga Agglomerate (Van Couvering, 1972). However, the grey-green matrix adhering to the specimen was not exposed on the hillside. Instead, patches of the matrix were found on top of the hill just above the Agglomerate. Since a major path crosses the top of the hill, the specimen was probably knocked down the slope (in one or several large pieces) by passing humans, cattle, or goats.
Materials and methods Overall, the specimen is beautifully preserved (see Figure 1). The only obvious distortion is due to (1) buckling and crushing of the left interorbital region; (2) slight, superior displacement of the right posterior portion of the palate in the vicinity of the greater of the left zygomatic (by 2-4 mm) along palatine foramen; and (3) d ownward displacement Otherwise, the specimen preserves much of the the zygomaticomaxillary suture. premaxilla and maxilla, all of the postcanine dentition except the crown of RPs, and most of the left zygomatic including half of the inferior orbital margin. Four fragments from the nasal/interorbital region are fastened together but cannot be attached to the rest of the specimen. Dental, palatal, and facial measurements were taken with a set of Fowler “Max-Cal” digital calipers. Measurements were generally the same as those described by Andrews (1978) and Pilbeam (1969). Any exceptions are noted in the text. To insure comparability of measurements, previously published measurements of Proconsul material were checked on original specimens in the National Museum of Kenya. Measurements that had to be estimated for the new material are noted by brackets in Tables 1 and 2. Comparisons are East African material preserving palatofacial made with previously-described morphology. However, in light of possible differences between Proconsul africanus from the Tinderet sites (such as Koru and Songhor) and specimens referred to Proconsul africanus from the Kisingiri/Rangwa sites (Rusinga and Mfangano) (Kelley, 1986; Pickford, 1986)) dental measurements for specimens from the two areas are presented separately in tables and figures. Specimen abbreviations are as follows: Kenya National Museum-KNM-RU (Rusinga), KNM-MW (Mfangano), KNM-SO (Songhor), KNM-KO (Koru formation), KNM-LG (Legetet formation), KNM-CA (Chamtwara member); KNM-KQ (Kapurtray formation); BM(NH)-British Museum (Natural History); UM-P-Uganda Museum, Primate Collection.
Palatofacial morphology The alveolar bone of the premaxilla is slightly eroded between the incisor alveoli. However, the border between the right and left central incisor alveoli is preserved well enough to yield an estimate of naso-alveolar height. That estimate (9.3 mm) is relatively low, even for Proconsul (see Table 1). Still, the incisors were probably no less procumbent than in other
HOMINOID
FACE FROM RUSINGA
ISLAND,
463
KENYA
Proconsul specimens as evidenced by the slope of the naso-alveolar clivus (approximately 40” to the tooth row) and the orientation of the incisor alveoli within the premaxilla. The alveolar border between the right canine socket and the right lateral incisor is also well-preserved with a sizeable diastema (6.5 mm) (see Figure Id), larger than that of any specimen referred to P. africanus (Andrews, 1978) and well within the range observed b) Andrews (1978) for P. n_yanZaeand P. major. Table 1
Palato-facial Measurements (comparative measurements Andrews 1978; Pilbeam 1969; Whybrow and Andrews 1978) KNM-RU 16000 Naso-alveolar height Naso-alv. hr./M’-M’s Nasal aperture height Nasal aperture breadth Nasal apert. br./ht. Zygomatic arch height Maxillary Maxillary Maxillary Palate Palate Palate (br. at (br. at Depth Depth
sinus length sinus breadth sinus br./ I.
length breadth at canine breadth at M? C)/(br. at M2) M*)/length at C/P’ at My
Inter-orbital breadth Inter-orb./Xasal ap.br. Inter-orb./Pal.br. at M’ Inter-orb./C-Mjlength Ml-M3 length Ps-Ms length C-M3 length * Measurements restoration [] = estimates
16.0
F9.31 [31,2%]
[G] 20.0 64.5% 17+*
1321 22.8 [71.3%]
I I.2
11.1 41.5% 19.6 14-o 71.5% 7.1
l6.i 45.5% [361 30.2 84.0% 14.0 46.0 I 7.0 37.0%
__ 45.0 19.0 23.6 80.5% 524% 5.1 6.8
79.0 37.0 33.4 110.8% 43.6% 4.0 7.5
24.8 124.0% 85.3% 41.0%
18.0 128.6% 76.3% 40.5%
20.0 66.2% 6 I .6% 27.1%
33,2* 46.8* 60.5
25.8 365 44.4
66.0* 29.8 29. I 102.3% 48.5% * 7.0* 8.5
[27,4]
[ 120,2%]
Andrews
UM-P 62-1 I
Il.2
58.6 28.6 28.4 100.7% 48.5% 5.1 7.3
[96,5% [50,8%]
KNM-RU 7290
_
133.4) 13.8 41.3%
29.8 41.6 53.9 from
BM(NH) Ml6647
from
1
11978) on BM(NH)
36.7 54.6 73.7 Ml6647
befre
Posteriorly, the premaxilla and maxilla form an incisive foramen like that in other P~ocon.wl specimens (Ward & Kimbel, 1983; Ward & Pilbeam, 1983). The subnasal alveolar process of the premaxilla ends well-anterior to the front edge of the palatine processes of the maxillae leaving a large incisive foramen (maximum diameter 9.4 mm) and effectively no incisive canal (see Figures 1c and Id). As in the Moroto palate (UM-P 62- 11) originally attributed to P. major (Allbrook & Bishop, 1963),1 broad, shallow grooves run anteriorly from the incisive foramen along the inferior surface of the subnasal alveolar process on either side of the midline. Superiorly, the nasal processes of the premaxilla extend up the lateral walls of the nasal aperture. As in the 1948 skull of P. afticanus (KNM-RU 7290)) the premaxillary-maxillary 1Since the taxonomic assignment ofthis specimen to P. major has been disputed in the literature (Leakey, 1963; Martin, 1981), it will merely be referred to as either the Moroto palate or specimen UM-P 62-11 in this paper.
464 Table 2
M. F. TEAFORD
ET AL.
Dental measurements (Pan measurements taken from Pilbeam, 1969; Proconsul measurements taken from Andrews, 1978, incorporating changes/additions described by Kelley, 1986; Martin, 1981; Pickford, 1986)
Species (sites)(ilr)
Mean MD Length (mm) (2 S.D.)
Mean BL Breadth (mm) (+
SD.)
Canine P. africanus (Tinderet) (5) P. ajkicanus (Rangwa) (9) KNM-RU 16000 P. tzyanzae ( 10) Pan (males) (14) Pan (females) (11)
10.7 f 1.1
8.1 + 0.7
9.2 + 0.5
7.2 ?C0.5
14.5 13.2 f 1.1 14.0 + 1.2 11.3kO.5
11.7 10.5 _+ 0.9 10.9 f 1.3 8.9 + 0.3
PJ P. africanus (Tinderet) (2) P. africanus
6.5 + 1.3
8.6 f 1.1
5.9 f 0.3
9.0 + 0.7
(Rwzwa) (3) KNM-RU 16000 P. nzantae (5) Pan (males) (13) Pan (females) (11)
6.7 7.3 + 0.5 8.1 f 0.6 7.9 + 0.4
I@2 10.8 k 0.4 10.5 f 0.5 10.5 f 0.6
P4 P. africanus (Tinderet) (2) P. ajicanus (Rang+ (6) KNM-RU 16000 P. nyanzae(11) Pan (males) (13) Pan (females) (11)
5.7zk0.1
9.3 + 0.4
5.4f 0.4
9.1 + 0.7 104 10.7 1; 0.7 10.2 + 0.4 10.2 f 0.3
6.1 6.6 f 0.6 7.0 + 0.3 7.0 + 0.3
M' P. africanus (Tinderet) (7) P. africanus (Rangwa) (IO) KNM-RU 16000 P. nyancae(8) Pan (males) (12) Pan (females) (11)
7.7+ 0.6
9.0 f 0.4
7.8+ 0.5
9.2 + 0.6 10.0 10.6 f 0.7 11.2f0.5 11.2+@6
8.5 8.9 f 0.3 9.9 f 0.5 98 + 0.5
M4 P. aficanus (Tinderet) (5) P. afiicanus (Rangwa) (11) KNM-RU 16000 P. nyanzac(5) Pan (males) (13) Pan (females) (11)
8.9+ 0.5
ll.OkP5
8.4f 0.7
IO.1 AZ0.9 11.7 12.2 + 1.1 11.7+@5 11.4 ?r 0.7
10.6 10.9 f 1.1 10.2 f 0.7 10.0 f 0.6 MS
P. ajicanus (Tenderet) (4) P. africanus (Raw-) (4) KNM-RU 16000 P. nyanzae(8) Pan (males) (11) Pan (females) (9)
8.2 + 0.3
IO.8 + 0.8
8.2 + 0.5
10.6 f 0.5
10.5 11.1 + 1.1 9.2 f 0.6 9.0 + 0.6
12.2 13.3 f 1.1 11.0 + 1.0 10.9 f 0.6
HOMINOID
FACE
FROM
RUSINGA
ISLAND,
KENYA
465
sutures are clearly visible in anterior view showing that the nasal processes of the premaxilla formed most of the lateral wall of the nasal aperture. The aperture itself is wider than that of the holotype of P. nyanzae (see Table l), but probably not as high, although with the buckling of the left interorbital region the latter measurement is difficult to estimate. Ir any case, the aperture is significantly larger than the only one available for P. u.anus (KNM-RU 7290). The base of the aperture resembles the broad, gutter-like base of the Moroto palate (Pilbeam, 1969) rather than the narrow, seam-like base noted by LeGros Clark and Leakey (1951) for P. africanus (KNM-RU 7290). Probably the most striking features of the face of this specimen are the pronounced canine juga dominating the anterior part of the maxillae (see Figures 1b and 1d). While the inferolateral wall of each canine socket is broken away, the maxillae still show marked concavities posterior to each canine jugum. The premaxillae also show slight concavities anterior to each canine jugum, and in this respect, KNM-RU 16000 differs slightly from the restored holotype of P. nyunzue which exhibits a more convex surface in this area. As Ward & Pilbeam (1983) have noted, many factors can influence the development of canine fossae. In the case of KNM-RU 16000, it should be noted that the canines were probably implanted in a similar fashion to those of the restored holotype of P. nyunzue-i.e., with roots tilted slightly towards the midline and almost no external rotation (see Figures la and Id). Thus, the concavities anterior to the canine juga may reflect a slightly more procumbent premaxillary region. The remainder of the alveolar processes of the maxillae are intact except for a tiny fragment distal to RMs. The palate is larger than that of specimens attributed to P. africanus (BM[NH] M14084, KNM-RU 7290) but not quite as large as that of the restored holotype of P. nyanzae (see Table 1). It narrows slightly at the level of P4, but overall the tooth rows are essentially parallel. The ratio of palate breadth at the canines to palate breadth at M* is 10@7’~~, which is noticeably different from Andrews’ (1978) estimates for the 1948 skull of P. africanus and is closest to that for the restored holotype of P. nyanZae (Whybrow & Andrews, 1978) (see Table 1). The depth of the palate is similar to that for other Proconsul specimens which are, in turn, much shallower than those of modern great apes (Pilbeam, 1969). Most ofthe sutures of the palate are still visible (see Figure Id), although the premaxillae were originally broken from the maxillae along much of the premaxillary-maxillary suture in this specimen. The intermaxillary suture is visible in its entirety. The greater palatine foramen lies opposite the mesial part of Ms and, on the left side, the maxillopalatal suture is clearly visible moving anteriorly from the foramen to a point opposite mid-M* before turning abruptly towards the midline. The anterior part of the right maxillopalatal suture is visible, but most of the right palatine is missing. Most of the interpalatine suture is preserved. Large portions of the medial and lateral walls of the maxillary sinuses are missing in KNM-RU 16000. In addition, the floor of the right maxillary sinus has not been cleaned of matrix. Still, the floor of the left maxillary sinus and extensions of the sinus into the root of the left zygoma allow a better appreciation of the form and extent of the sinus than has been possible before. In fact, the superolateral corner of the sinus is also visible near the inferolateral margin of the orbit. This reaffirms Pilbeam’s (1969) observations on the extent:of the maxillary sinus based on isolated fragments associated with the Moroto palate. The floor of the maxillary sinus extends from the distal edge of P4 into the maxillary tuberosities (as visible on the small portion of tuberosity on the right side). At its
466
M. F. TEAFORD
ET AI.
Figure 1. New Proconsul specimen (KX.M-RU 16000) from Rusinga Island, Kenya: a (top left), anterior view; b (bottom left), left lateral view; c (top right). superior vie\\,. d (bottom rqht), inferior view.
468
ET AL.
M. F. TEAFORD
anterior-most point, the floor of the sinus lies well above the roots of P4 and Mr. It then ridge over the slopes down to a slight excavation above M*; it rises in a transverse mesiobuccal root of M3; and then descends into another shallower excavation above Ms. The alveolar bone over the distobuccal roots of both Ms’s projects into the sinus. The floor of the maxillary sinus of the new specimen is thus slightly more irregular than that of certain Proconsul specimens (e.g., KNM-RU 2036), but it still does not approach the degree of convolution of other specimens (e.g., KNM-RU 1677A), and it certainly is not multilocular as in modern great apes (Pilbeam, 1969). The root of the zygoma arises above M* (see Figure Id). As Andrews (1978) has noted, this is the usual condition in P. nyaneae and modern great apes, but it contrasts with that in P. africanus. As mentioned above, the zygomatic bone is displaced downward slightly along the zygomaticomaxillary suture; as a result, its orbital process is probably twisted slightly posteriorly. Still, the face must have been set at an angle of 50-60” to the plane of the teeth (as estimated from a line running along the anterior surface of the orbit and a line between the center of the crowns of Ps and Ml) (see Figure 1b), and this value is similar to estimates from the restored holotype of P. nyanzae (Whybrow & Andrews, 1978) and the Moroto palate (Pilbeam, 1969). Th e inferior margin of the zygomatic is roughened and slightly excavated for the origin of the superficial masseter. Precise measurements of the interorbital region are extremely difficult due to the crushing and buckling on the left side and the fact that the four nasal/interorbital pieces cannot be firmly attached to the rest of the face. Nonetheless, the most inferior part of the anterior lacrimal crest is preserved on the left side, and the most superior part ofthe crest is preserved on the right side together with portions of inter-nasal suture. Thus, an estimate ofinterorbital breadth can be made by measuring the distance from the crest to the midline on the right side and doubling that figure (see Table 1). This is roughly comparable with the measurements provided by Pilbeam ( 1969) and Whybrow & Andrews ( 1978), although their measurements were probably taken inferior to the one used here. The main point is that the interorbital breadth of KNM-RU 16000 is probably larger than that of the restored holotype of P. nyanzue, and it is certainly larger than that of the 1948 skull of P. africanus (KNM-RU 7290)*. These differences are even more striking when considered in light of the relatively small palate and tooth rows of KNM-RU 16000. For instance, the ratio of the interorbital breadth to the internal palate breadth at M2 is much larger than that for the holotype of P. nyanzae (see Table 1)
Dentition Since the anterior teeth are missing from this specimen, the bulk of this description will concentrate on the postcanine teeth. However, given the importance of canine size differences in interpretations of primate morphological variability, a few words must be said about canine size in KNM-RU 16000. Canines
Measurements of the maximum length of each canine alveolus and estimates of the left canine alveolus show that the canines ofthis specimen were not only larger than those of any Rusinga specimen of P. ajicanus, they were also larger any specimen of P. nyanzae except the holotype (see Figure 2a). This is despite 2 The interorbital breadth of KNM-RU new values are presented in Table 1.
7290 was increased
in a recent reconstruction
of the width significantly than those of the fact that
(Walker ct al., 1983). The
HOMINOID
FACE FROM RUSINGA
ISLAND,
KENYA
469
KNM-RU 16000 has a relatively small palate and its postcanine teeth are intermediate in size between P. a&anus and P. nyanzae (see below). Given the relative size of its canines, this individual must certainly have been a male. Premolars
The crown of RPs is broken-off near the cervical margin, and it was never recovered in sieving at site R107. However, the crown of LPs is in excellent condition, showing only a slight degree of wear and a small dentin exposure on the tip of the paracone. Morphologically, the Ps of KNM-RU 16000 is most similar to those assigned to P. nyanzae, although it lies at the low end of the size range for that species (see Figure 2b). As in all Proconsul specimens, the paracone is taller than the protocone, but that difference is not as marked as in most specimens of P. africanus and P. nyaneae. The paracone is also not as slender and projecting as in the holotype of P. africanus from Koru (BM[NH] M14084). The mesial and distal crests of the paracone are well-developed, with small tubercles at their mesial and distal ends, respectively. However, the mesiobuccal flange is not as pronounced as in some specimens of P. nyanzae and P. major. The mesial and distal crests of the protocone are nearly absent, but small wear facets suggest that some form of shearing was still occurring along these edges. A slight transverse ridge connects the protocone and paracone and it separates a tiny, vertical,, mesial fovea from a larger distal fovea. The enamel of the distal fovea is slightly ,wrinkled, leaving three faint ridges running distolingually from the paracone into the fovea. The enamel of RP4 is eroded or etched, but most morphological features are still visible on it. The LP4 is in excellent condition, with no dentin exposures but a moderate degree of faceting on the distal protocone. In terms of standard length and width measurements, the P4 of KNM-RU 16000 is intermediate in size between those assigned to P. afticanus and P. nyaneae (see Figure 2~). Morphologically, P4 is fairly similar to Ps, thus only the differences will be mentioned here. As in other Proconsul specimens, the difference in height between the paracone and protocone on P4 is not as pronounced as that on Ps. This is due to a relative decrease in height of the paracone rather than a relative increase in protocone height. P4 has a more rounded, oblong appear’ance in occlusal view a8 compared with Ps in which the mesiobuccal flange gives the crown a more angular appeaiance and makes the mesial portion of Ps larger than that of Ph. The transverse ridge betweed the protocone and paracone of P4 is split by a groove running mesiodistally from the distal fovea. This, in conjunction with a slight wrinkling of the distal portion of the occlusal surface, leaves the transverse ridge of P4 less pronounced than that on Ps. Finally, the lingual cingulum on P4 is more developed than that on Ps, although it is not as distinct as those on the molars. Molars
As with the premolars, the molars on the left side of this specimen are generally i? much better condition than those on the right side. Specifically, RMl and the mesial half of RM2 are eroded and etched so that only the basic morphological features are discernible. The remainder of the right and left molar series is lightly etched in places but, overall, the teeth are in excellent condition. Ml has dentin exposures on all its cusp tips except for the hypocone. M* shows very little wear-just the slightest faceting along its occlusal ridges. Ms is not quite into occlusion although its buccal cusp tips show evidence of occasional tooth-food-tooth contacts. Ml is by far the smallest of the molars, lying at the upper end of the size range for specimens assigned to P. africanus (see Figures Id and 2d). Its cusps are essentially equal in
470
ET AL.
M. F. TEAFORD
Maxillary
14
canine
size in Proconsul and Pun
(a)
XX
12 -
l x l '4 ‘g x m
.
__
I
:: P.africanus-T P.africanus-R P.nvanzae &males &females KNM-RU 16000
..X@ .x . .
X
‘8*
0
61 8
l
x
X IO -
e
I
I
I
Maxillary
I
I
1
P3 size in Proconsul
12
ond Pun
.
(b)
X' b
3 0
Maxillarv
x
l l .
x
x,
__ a .
x
.
l
g 8
x x
xx
:
P4 size in Proconsul
and Pun
II
IO
5
7
6 Meslodistol
length
(mm.1
I II6
14
12
IO
47 Maxillary
MI size in Proconsul
and Pan
12, l*
- (d)
..
xxI
xx .
ox’
II -
P
x
lxx
II Maxillary M2 size in Proconsul
-
and fan
(e)
13 -
X .
x
x.
Er+ p El* Q
x ox*
x*
0
. .
7
8
IO
9
Maxillary
M3 size In Proconsul
and Pun
I6
X
I
8 7
I 8
I
I
I
9 Mesiodistol
II
I
IO
II
length
I,I
I I2
13
(mm.)
Figure 2. Scatterplots of mesiodistal length vs. buccolingual breadth for the maxillary teeth of KNM-RU 16000 and a comparative sample of Proconsul specimens and males and females of Pan frogfodylcs. Comparative specimens are the same as those in Table 2 which are taken from Andrews (1978), Martin (1981), and Pilbeam (1969). P. aficantcs-T = P. aficanur specimens from the Tinderet sites (SO, KO, LG, CA, KQ); P. ajicanur-R = specimens traditionally referred to P. aficanw from the Rangwa sites (RU and MW). a, Maxillary Canines; b, Ps; c, P4; d, Ml; e, M*; f, Ms.
472
M. F. TEAFORD
ET AL.
size although the metacone is noticeably taller than the other cusps. The trigon is not as well-defined as in P. u@xnus. However, the talon is probably better developed than in either P. africanus or P. nyunrue. Correlated with this is the fact that there is a large distal fovea on Mr and the hypocone is not isolated from the trigon as in many specimens of P. uficanus and P. nyunzue. As in other Procond specimens, the mesial fovea is bounded by two ridges running from the protoconule, to the paracone and the mesial edge of the tooth. However, the fovea and ridges are extremely small and the protoconule has essentially been obliterated by wear. The ridges along the buccal edge of the tooth are well-developed, but the intersection of the ridges joining the paracone and metacone is relatively high above the central basin as in P. nyunzue rather than deep within a buccal groove as described by Andrews (1978) for P. ufticunus. The lingual cingulum is fairly welldeveloped-running from the protoconule to the lingual side of the hypocone. As in other specimens of P. ujicunus and P. nyunzue, the distal cingulum blends into the talon while the buccal cingulum is reduced to a tiny shelf between the paracone and metacone. M* is certainly larger than Ml, but it is nearly equaled in size by Ms. It lies at the low end of the size range for P. nyunzue (see Figure 2e), and the ratio of M* and Ml size is closer to that for P. nyuneue than to that for P. ufricunus (see Table 3). Since the lingual side of the tooth is longer than the buccal side, M* has more of a rhomboid shape than Mr (see Figure Id). This is probably due to the fact that the protocone and protoconule are relatively large, and the hypocone and distal cingulum combine to extend the distolingual margin of the tooth slightly. Still, that distolingual bulge is not as marked as on certain specimens of P. major (e.g, KNM-CA 388, Martin, 1981). The occlusal ridges on the buccal side of M* are well-developed. However, the lingual boundaries of the trigon are relatively poorly-defined because thep are interrupted by the protoconule, metaconule, and the longitudinal sulcus. As on M*, two faint ridges from the protoconule outline a tiny mesial fovea. However, the hypocone retains a slight ridge to the protocone, but that ridge is split by a lingual groove that runs into the large distal fovea. The lingual cingulum is fairly large, showing moderate beading around the protocone and the mesial portion of the hypocone. Ms has a very small hypocone. However, a massive protocone and large lingual cingulum contribute to an overall occlusal area (mesiodistal length X buccolingual breadth) that is nearly identical to that of M*. Needless to say, the Ms of KNM-RU 16000 is certainly not the “greatly reduced” tooth that has traditionally been cited as a characteristic feature of P. ufn’cunus (Andrews, 1978). Nevertheless, it is still small by P. nyunaze standards (see Figure 2f). The small hypocone is barely recognizable, yet the paracone and metacone are ofreasonable size. Coupled with the massive protocone, the net result is a tooth that is dominated by the trigon and is nearly triangular in occlusal outline. The ridges that define the lingual boundaries of the trigon, however, are barely discernible since they are broken into segments by a prominent protoconule and metaconule. The mesial fovea is still quite small and the distal fovea is obstructed by small cuspules. The lingual cingulum is larger than that on M2 and is prominently beaded. Due to the small size of the hypocone, the lingual cingulum may appear to be larger than it actually is, since it forms a prominent border around the lingual side of the tooth.
Discussion With improvements in the fossil record, investigators are sometimes forced to deal with specimens that fall between established taxonomic categories. These intermediate forms
473
HOMINOID FACE FROM RUSINGA ISLAND, KENYA
not only give us a better understanding of morphological variation in extinct species, they occasionally force us to question some of the criteria used to make taxonomic distinctions. KNM-RU 16000 is such a specimen. Within the current taxonomic framework for Early Miocene hominoids, three alternative interpretations of this specimen are possible. I. KNM-RU 16000 as a male Proconsulnyanxae To some investigators, the question of what to do with this specimen will be an easy one. Nearly all of the traits traditionally used to distinguish Proconsul afficanus from Proconsul nyanzae indicate that KNM-RU 16000 is a Proconsul nyanpae. These include canine size, the relative sizes of the upper molars, relative development of occlusal ridges on the upper molars, Ps shape, palate shape, location of the root of the zygoma, and shape of the nasal aperture, (Andrews, 1978; LeGros Clark & Leakey, 1951; Whybrow & Andrews, 1978). This pattern of similarities also extends to most of the ratios of tooth size that have been used in analyses of Proconsul material and modern primate material (see Table 3). In fact, the only trait for which this specimen presents a problem is postcanine tooth size. Thus, while the palate is only slightly smaller than that of the restored holotype of Proconsul dentition is clearly intermediate in size between Proconsul nyaneae, the postcanine
Table 3
Ratios and sums of maxillary dental measurements for Proconsul and Pan. As in Table 2, measurements are taken from Andrews (1978) md Pilbeam (1969). Ratios and rums are the same aa those used by Greenfield (1972), Lucas et al. (1986), and Pickford (1986)
P. ajiicanus BM(NH) 14084* KNM-RU 1705 KNM-RU 1904 KNM-RU 1973 KNM-RU 2036 KNM-RU 7290 Mean k S.D. (all P. ufic.) (P. afic. from Rusinga) KNM-RU
16000
P. nyanzac BM(NH) 16647 KNM-RU 1674 KNM-RU 1677 KNM-RU 2088 Mean f S.D. Pan troglodytes males (range) females (range) Mean f S.D. males females * Type specimen
Canine area: M 1 area
P4 area: Ml area
M 1area: M3 area
Ml length: ML?length
Postcanine tooth area (P3-M3)
123.3 103.2
67.7 65.4
91.4 _ _ _ _
85.9
315.4 _ _ 377.6
265.9 264.3 + 1.6
Molar area (Ml-M3)
262.7 _
54.5 68.8
80.2
96.1 89.9 96.3 84.8
112.Ok8.4
64.1 f 5.7
85.8 + 5.6
90.6 + 4.9
3465 * 3.1
106.4 + 3.2
62.9 + 6.1
_
91.8 k 4.8
_
199.6
74.6
66.4
80.2
468.8
337.1
162.7 142.9 132.8 146.1 + 12.4
72.8 79.0 71.8 62.6 71.6 f 6.8
68.8 68.0 64.2 77.2 69.6 f 4.7
75.4 84.9 78.3 87.8 81.6 + 5.0
593.0 467.4 591.9 550.8 + 59.0
427.6 327.6 431.3 297.3 371.0 + 60.4
118 - 172.3 79 - 104.8
58.7 - 71.6 52.3 - 73.1
87.3 - 135.3 89.6 - 121.8
85.6 - 109.7 91.6 - 108.3
451.9 - 529.1 431.4 - 526.9
300.3 - 367 292.7 - 358.5
97.4 f 6.4 98.8 + 4.8
487.6 + 26.2 475.1 f 31.3
332.7 zk 23.3 318.7 + 24.3
109.6
147.3 zk 17.1 91.6+ 8.1
6.57 f 3.5 64.8 + 5.2
109.1 + 15.4 11@9f 11.3
of P. ajicanus from Koru; all other Proconsul specimens
_
in this table are from Rusinga
474
M. F.
TEAFORD
ETAL.
nyanzae and Proconsul africanus. Again,
that may not pose problems for some investigators, because KNM-RU 16000 could simply be a small Proconsul nyanzae. Yet, KNM-RU 16000 was presumably a male, and its canines were probably larger than those of any known specimen ofProconsul nyanzae except the holotype. It would be unusual for such a specimen to have among the smallest postcanine teeth in its species (e.g., see ratio of canine area: Ml area in Table 3). Finally, if this specimen were to be assigned to P. nyanzae, it would still leave us with a male-dominated P. nyanlae sample and a female-dominated P. africanus sample from Rusinga (Bosler, 198 1).
2. KNM-RU 16000 as a male of the small species of Proconsuljom Rusinga Another alternative would be to say that KNM-RU 16000 is not a Proconsul nyanzae but instead the first male specimen of the smaller species of Proconsul from Rusinga-i.e., that traditionally viewed as Proconsul africanus. This interpretation would avoid some of the problems inherent in assigning the specimen to Proconsul nyantae. For instance, the relative size of the canines might be used as a distinctive characteristic of males of such a species. However, this interpretation would also create some problems. Most notably, it would ignore all of the morphological criteria that have traditionally been used to make the distinction between Proconsul nyantae and Proconsul africanus, and it would do so without providing an alternative set of criteria for distinguishing between these species. Needless to say, it would certainly reinforce the idea that the small species of Proconsul from Rusinga is not Proconsul aficanus (Kelley, 1986; Pickford, 1986)) since the holotype of that species (from Koru) is also a male. Finally, it would still leave us with the important question raised by Bosler (1981): given the excellent Miocene hominoid fossil collections from Rusinga, why has it taken so long to find a male of this species? 3. KNM-RU
16000 as a male Proconsul
nyanzae
as de3ned by Kelley and by Pickford (Kelley,
1986; Kelley & Pilbeam, 1986; Pickford, 1986)
A new approach to this problem would be to say that although KNM-RU 16000 is definitely a Proconsul nyaneae, investigators have, until recently, been defining Proconsul nyanzae too narrowly. In other words, as both Kelley and Pickford (Kelley, 1986; Kelley & Pilbeam, 1986; Pickford, 1986) have suggested, perhaps we have underestimated the range of variation in this species, and all of the Proconsul specimens from Rusinga are Proconsul nyanzae, while Proconsul aficanus is found only at sites such as Koru and Songhor. From such a perspective, KNM-RU 16000 would merely be a small male Proconsul nyanzae albeit with large canines, while the females of that species would be the specimens from Rusinga traditionally referred to Proconsul ajicanw. As Kelley and Pickford admit, as far as dental metrics are concerned, this interpretation might require a greater degree of sexual dimorphism than that exhibited by modern baboons and gorillas. Furthermore, preliminary analyses of newly-discovered Proconsul material from Rusinga show that the dentition may be even less variable than the postcrania as far as size differences are concerned. For instance, initial analyses of the new wrist material (Beard et al., 1986) s h ow little more than size differences between specimens attributed to P. nyanzae and P. aficanus. However, those size differences range from 1.5 : 1 to 2 : 1 (for linear dimensions) depending on which bones are examined. Such size differences would be greater than those between males and females in modern hominoids, where ratios of 1.3 : 1 are generally the maximum (McHenry, 1986). M oreover, estimates of body weight
HOMINOID FACE FROM RUSINGA ISLAND, KENYA
475
based on allometric relationships with long bone cross-sectional dimensions (Ruff, in press) yield estimates of 9.6 kg for P. a&cams and 3 7 kg for P. nyanzae (based on analyses of two individuals per species). This reaffirms Walker & Pickford’s (1983) estimates of a 4 : 1 difference in body weight between these species (cf. Kelley, 1986; Pickford, 1986). Such body-size dimorphism within a single species is unprecedented in modern land mammals. Since body size itself is an important determinant of degree ofdimorphism (Leutenegger & Cheverud, 1985), such sexual dimorphism in a primate of this size would seem highly unlikely. For instance, published weights for Papio (Jungers, 1985; Leutenegger & Cheverud, 1982) yield estimates of body size dimorphism averaging less than 2: 1. As a correlate of such body size dimorphism, we would be left with a new, composite species made up of small females with relatively large teeth and very large males with relatively small teeth, Once again, Kelley and Pickford’s model would require that we revise our criteria for distinguishing between Proconsul nyanzae and Proconsul a&anus, as the traditional criteria would most effectively distinguish Rusinga males from Rusinga females within the same species. Summary
and conclusion
Given the problems with the alternative interpretations of KNM-RU 16000, perhaps the time has come to accept the fact that something is wrong with the criteria that have traditionally been used to distinguish between these species (see Kelley, 1986; Pickford, 1986 for reviews of this topic). A stable taxonomy for Proconsul will need larger samples and more associated material, and it should not overemphasize dental traits. Ontogenetically variable traits such as maxillary sinus morphology (Ward & Brown, 1986; Ward & Pilbeam, 1983) will have to be evaluated differently. KNM-RU 16000 includes a palate and partial face together with most of the maxillary dentition, yet its relatively large canines and relatively small posterior teeth make it an unusual specimen that is hard to assign to a known species. For the time being, this problem is best viewed in light of recent discoveries ofpostcranial material from Rusinga (Beard et al., 1986; Walker et al., 1985). As noted above, size differences in the new postcranial material indicate that there are two speciesof Proconsul on Rusinga. If we accept that assessment, then we can at least use the more complete craniodental material’(such as KNM-RU 16000) to produce a sample of males and females of each species on Rusinga. From this perspective, the most reasonable conclusion would be to view KNM-RU 16000 as a male of the smaller species of Rusinga Proconsul, although, clearly, such as assignment should be viewed with a great deal of caution. Analyses of new postcranial material from Rusinga may lead to the discovery of important differences between Proconsul species in functional complexes other than the jaws and teeth. Even if no functional differences are discovered, perhaps size differences will be of critical importance, for, as far as skeletal morphology is concerned, some modern species differ in little more than size (e.g., within the genus Cercopithecus). In any case, KNM-RU 16000 will play a pivotal role in future discussions of Proconsul taxonomy. Its unique combination of features has re-emphasized the view that we must look at all the evidence provided by cranial andpostcranial material, and we must not overlook our only modern primate analogues. Acknowledgments We thank the Government Governors of the National
of Kenya for permission to carry out research in Kenya and the Museums of Kenya. We thank Bw. Kamoya Kimeu and his
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M. F. TEAFORD
ET
AL.
team for invaluable help in the field and at the National Museum in Nairobi. Many colleagues helped in various ways, but special thanks go to Peter Andrews, Bobbie Brown, Eric Delson, Dick Hay, Bill Jungers, Jay Kelley, Meave Leakey, Lawrence Martin, Emma Mbua, Mike Rose, Chris Ruff, Blaire Van Valkenburgh, and Steve Ward for help, useful discussions, and/or comments on the manuscript. We also wish to thank three anonymous reviewers for their helpful comments on the manuscript. This work was supported by the National Museums of Kenya and NSF Grant BNS 8418567. A. W. was also supported by a John Simon Guggenheim Memorial Fellowship during portions of this study.
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