Principal Components Analysis of Distal Humeral Shape inPliocene to Recent African Hominids: The Contributionof Geometric Morphometrics

ANNE-MARIE BACON*EP 1781, Dynamique de l’Evolution Humaine, 75014 Paris, and Collegede France, 75005 Paris, France

KEY WORDS Australopithecus; humerus; geometric morphomet-rics; landmarks; principal components analysis

ABSTRACT The shape of the distal humerus in Homo, Pan (P. paniscusand P. troglodytes), Gorilla, and six australopithecines is compared using ageometric approach (Procrustes superimposition of landmarks). Fourteenlandmarks are defined on the humerus in a two-dimensional space. Principalcomponents analysis (PCA) is performed on all superimposed coordinates. Ihave chosen to discuss the precise place of KNM-KP 271 variously assignedto Australopithecus anamensis, Homo sp., or Praeanthropus africanus, incomparison with a sample of australopithecines. AL 288-1, AL 137-48 (Ha-dar), STW 431 (Sterkfontein), and TM 1517 (Kromdraai) are commonlyattributed to Australopithecus afarensis (the two former), Australopithecusafricanus, and Paranthropus robustus, respectively, while the taxonomicplace of KNM-ER 739 (Homo or Paranthropus?) is not yet clearly defined. Theanalysis does not emphasize a particular affinity between KNM-KP 271 andmodern Homo, nor with A. afarensis, as previously demonstrated (Lague andJungers [1996] Am J Phys Anthropol 111:479–487, 2000.© 2000 Wiley-Liss, Inc.

In this study, the shape of the distal hu-meral extremity of large-bodied, modernHominoidea (Pan troglodytes, Pan paniscus,Gorilla gorilla, and modern Homo) is com-pared with that of six fossil hominids (AL288-1, AL 137-48, KNM-KP 271, TM 1517,KNM-ER 739, and STW 431), with a geo-metric morphometric approach: Procustessuperimposition of landmarks. One princi-pal advantage of this approach is the treat-ment of shape as a whole by using coordi-nates of homologous landmarks defined onthe contour of the distal humerus. In thisrespect, the geometry of the bone is pre-served, and the variation of its differentstructural parts (trochlea, capitulum, andepicondyles) can be simultaneously anal-ysed by principal components analysis(PCA) of superimposed coordinates. By tak-ing into account the size parameter (cen-

troid size), australopithecines and modernhominoids can be compared morphometri-cally, with respect to form and function.

Since the first description by Pattersonand Howells (1967), most scientists haveagreed that KNM-KP 271 possesses someHomo-like features (McHenry and Corru-cini, 1975; Day, 1978; Senut, 1979; Leakeyet al., 1995, 1998). However, the systematicattribution either to Homo sp. (Day, 1978),Australopithecus anamensis (Leakey et al.,1995, 1998), or even Praeanthropus africa-nus (Senut, 1995), reflects the real difficultyin determining its closest affinities both

Grant sponsor: Foundation Singer Polignac.*Correspondence to: Anne-Marie Bacon, EP 1781, Dynamique

de l’Evolution Humaine, 44 rue de l’Amiral Mouchez, 75014Paris, France. E-mail: bacon@ivry.cnrs.fr

Received 22 September 1998; Accepted 6 December 1999.

AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY 111:479–487 (2000)

© 2000 WILEY-LISS, INC.

with modern and fossil hominids. Its prove-nance, from deposits dated around 4.12–4.17 million years ago in Kanapoi, Kenya(Leakey et al., 1998), raises in particular thequestion of the direct ancestry of A. ana-mensis to the Homo lineage. If some authorsare convinced of this phyletic relation toHomo (Day, 1978; Senut, 1979; Senut andTardieu, 1985), others, in support of newdiscoveries in Kanapoi and Allia Bay, arerather inclined to consider A. anamensis asa possible ancestor of A. afarensis (Leakeyet al., 1995, 1998), while still others do notfind any particular morphologic resem-blances to modern Hominoids and considerKNM-KP 271 more australopithecine-like(Lague and Jungers, 1996). Because of thisambiguity, my aim was first to determinewhether the analysis of the humeral con-tour in a geometric perspective supports thecloser affinity of KNM-KP 271 to Homorather than to apes. Second, I sought todetermine the precise phyletic relationshipof KNM-KP 271 with other australo-pithecines, which in this study are repre-sented by five specimens commonly attrib-uted to four different taxa, Australopithecusafarensis (AL 288-1m and AL 137-48a), Aus-tralopithecus africanus (STW 431), Paran-thropus robustus (TM 1517e), and Paran-thropus boisei or Homo (KNM-ER 739).

Using an exact randomization procedurefor the analysis of variation among Plio-Pleistocene hominid distal humeri, Lagueand Jungers (1996, p. 402) observed: “Sub-sequent analyses further support the infer-ence that KNM-ER 739 and KNM-ER 1504are different from the other hominid humeriand possess a unique total morphometricpattern.” This result, suggested before byMcHenry and Corruccini (1975), called intoquestion the functional and morphologic

pattern defined by Senut and Tardieu (1985)for the “robust” australopithecine specimens(including TM 1517 and KNM-ER 739, andalso KNM-ER 1504 and KNM-ER 3735). Inthe same paper, the authors further added,“TM 1517 is most similar to one of the Hadarspecimens of A. afarensis (AL 137-48),whereas the first specimen of A. africanus(STW 431) is not closely linked to any of theother australopithecines.” Faced with newproblems and disagreement, this morphomet-ric analysis is an attempt to assess morpho-logical differences and similarities among thesix specimens of fossil hominids, in order toclarify their phylogenetic relationships.

MATERIALS AND METHODSMaterials

The sample is comprised of a homoge-neous human population studied in the St.Brydes crypt in London (n 5 73), three spe-cies of African apes studied in Tervuren, i.e.,Pan paniscus (n 5 20), Pan troglodytes (n 522), and Gorilla gorilla (n 5 26), and by thesix well-preserved humeri of Plio-Pleisto-cene hominids, including both casts (AL288-1m and AL 137-48a from Hadar,KNM-KP 271 from Kanapoi, and KNM-ER739 from Koobi Fora) and originals (TM1517 from Kromdraai and STW 431 fromSterkfontein) (Table 1).

Methods

Photographs of the distal extremity of thehumerus in inferior view were taken withthe same orientation for all specimens. Thehumerus is oriented with reference to thebiepicondylar line. Following the classifica-tion of Bookstein (1991), all landmarks be-long to type II (maxima of curvature) andtype III (constructed points due to the pro-jection of the contour used).

TABLE 1. List and systematic attribution of fossil hominids

Individuals Origin Description and systematic attribution

AL288-1mAL137-48a

Hadar, Ethiopia Australopithecus afarensis (Johanson et al., 1982)

KNM-KP 271 Kanapoi, Kenya Australopithecus anamensis (Leakey et al., 1995)Homo sp. (Day, 1978; Senut, 1979)Praeanthropus africanus (Senut, 1995)

KNM-ER 739 East Rudolf, Ileret, Kenya Paranthropus boisei (Leakey, 1971, 1973) or HomoSTW 431 Sterkfontein, Southern Africa Australopithecus africanusTM 1517 Kromdraai, Southern Africa Paranthropus robustus (Straus, 1948)

480 A.-M. BACON

Fourteen landmarks were selected on thecontour of the epiphysis in inferior view(Fig. 1): 1) the junction between the lateralepicondyle and the capitulum humeri, 2) themost lateral point of the capitulum humeri,3) the apex of the capitulum which is themaximum curvature of the capitulum in in-ferior view, 4) the capitulum groove, 5) theanterolateral margin of the trochlea, 6) thegroove of the trochlea in the anterior aspect,7) the anteromedial margin of the trochlea,8) the junction between the trochlea and themedial epicondyle, 9) the most salient pointof the medial epicondyle, 10) the posterome-dial margin of the trochlea, 11) the groove ofthe trochlea in the posterior aspect, 12) theposterolateral margin of the trochlea (prom-inence of the lateral trochlear ridge), 13) thejunction between the capitulum and theposterolateral margin of the trochlea, and14) the most salient point of the lateral epi-condyle.

Landmarks were digitized using a two-dimensional (2D) digitizing table and theDS-DIGIT program (Slice, 1994a). The cen-troid size (Bookstein, 1991) was computedas the logarithm of the square root of thesum of squared distances from the centroidto each landmark (Gower, 1975). All rawcoordinates were superimposed with theProcrustes method (Gower, 1975; Rohlf andSlice, 1990; Goodall, 1991). A generalizedleast-squared fit (GLS) was computed usingGRF-ND software (Slice, 1994b): an itera-tive procedure fits the entire sample to anestimated average configuration (dotted-line configurations in Figs. 2, 3). A new av-

erage consensus is estimated at the end ofeach iteration. Superimposed coordinateswere analyzed by principal componentsanalysis (PCA) of the covariance matrixwith NTSYS-pc software (1992). Extremedeformations were computed using GRF-NDin order to illustrate the shape variationalong each axis of the PCA (solid-line defor-mations, Figs. 2, 3).

RESULTS

PCA of shape differences

The first four axes explain 60.3% of thetotal variance: 30.4%, 12.8%, 9.6%, and7.2%, respectively.

The first plot (axis 1/axis 2; Fig. 2) clearlydivides three groups with a limited overlap:modern Homo, great apes (Pan, Gorilla),and fossil hominids. The first axis revealstwo main humeral shapes: Homo on oneside, and apes (Pan, Gorilla) and fossilhominids together on the other side. Thevariation mainly concerns the proportions ofthe medial (landmarks 8, 9) and the lateral(landmark 14) epicondyles, the extension ofthe capitulum in inferior view (landmark13), and to a lesser degree the depth of thegroove of the trochlea humeri (landmarks 6,11). Compared with the trochlea and thecapitulum, the proportions of both epicon-dyles appear relatively smaller in apes andaustralopithecines than they are in modernHomo. Also, in apes and australopithecines,the position of both epicondyles is also moreanterior, relative to the joint surfaces, withthe lateral epicondyle salient laterally

Fig. 1. a: Location of the fourteen landmarks on the humeral contour in two dimensions. b: Averageconfiguration.

PCA OF DISTAL HUMERAL SHAPE 481

(landmark 14); the trochlear groove is deep(landmarks 6, 11); the lateral margin of thetrochlea is more “sagittally” oriented (land-marks 5, 13). In Homo, we find the oppositecharacteristics: anteroposteriorly large epi-condyles but not salient (especially the lat-eral one), a shallower trochlear groove, anoblique lateral trochlear margin, and aweak extension of the capitulum.

Concerning axis 2, fossil hominids differfrom modern apes. In chimpanzees, the re-lief of the trochlea in the anterior aspecttends to be better developed than in fossilhominids (landmarks 5–7), and the medialepicondyle appears somewhat posterior(landmark 9) relative to joint surfaces. Theposterolateral trochlear crest (landmarks12, 13) is situated more medially in apesthan in fossil hominids, accentuating thewidth of the trochlea in the latter.

The second plot (axis 3/axis 4; Fig. 3) dis-tinctly reveals three groups among modernapes: Pan troglodytes, Pan paniscus, andGorilla gorilla, modern Homo and fossilhominids largely overlapping them all.KNM-KP 271 is located outside the varia-tion of the two Pan species, but at the mar-

gin of the variation of Gorilla and Homo. AL137-48 falls within the variation of Pan pa-niscus, whereas AL 288-1 appears interme-diate between ranges of variation of the twoPan species. TM 1517, STW 431, andKNM-ER 739 fall grouped within the rangeof variation of Pan troglodytes.

Axis 3 separates gorillas from chimpan-zees (Pan paniscus and Pan troglodytes).This concerns the development and exten-sion in inferior view of the capitulum (land-marks 1–5, 13), in correlation with thedepth of the trochlear groove (landmarks10, 11) and the position of the medial epi-condyle (landmark 9). Seen from below, Go-rilla exhibits a proportionally small capitu-lum with a mediolaterally large trochlea.Conversely, Pan paniscus and Pantroglodytes exhibit large, well-developed ca-pitula, and anteroposteriorly massive troch-leas.

Axis 4 separates Pan troglodytes fromPan paniscus only on the basis of the medialprojection of the medial epicondyle (land-mark 9), which is more marked in the latter.

KNM-ER 739, TM 1517, STW 431, andKNM-KP 271, which share with Pan troglo-

Fig. 2. Principal components analysis of superimposed landmarks for axis 1 (30.4%) and axis 2(12.8%). Plots of extreme deformations (solid lines) are associated with each axis. Dotted lines correspondto the mean reference configuration. 1, AL 288-1; 2, AL 137-48; 3, TM 1517; 4, STW 431; 5, KNM-KP 271;6, KNM-ER 739. Convex hulls are depicted for the main taxonomic groups.

482 A.-M. BACON

dytes a medial epicondyle which is not well-developed medially, differ from the Hadarspecimens on the basis of this feature.

DISCUSSION

Morphometric analysis of the distal hu-meral extremity in a sample of modernhominoids and fossil hominids was under-taken to determine whether KNM-KP 271 iscloser to Homo than to apes. Also to bedetermined was whether the morphometricapproach could identify the specific phyleticrelationships of KNM-KP 271 within theaustralopithecines.

Discrimination among taxa

The first PCA plot undeniably confirmsthat australopithecines are morphologicallyhomogeneous, especially if we take into ac-count that the degree of overlap in the hu-meral contour in humans, apes, and austra-lopithecines is minor. This agrees with thedata of Hill and Ward (1988), who suggestedthe difficulties involved in sorting fossil hu-meri. Lague and Jungers (1996), who usedcanonical variates analyses of Hominoid hu-

meri (P. troglodytes, G. g. gorilla, G. g.beringei, and Native and African Ameri-cans) with a larger fossil sample, previouslyemphasized the same results. In my analy-sis, australopithecines are unique amongHominoids, having a particular combinationof features, illustrated along axes 1 and 2,such as a medial epicondyle placed moreanteriorly relative to the joint surfaces, anda trochlea which is weakly developed an-teroposteriorly (Fig. 2).

But globally, taking into account thegreater part of variance in axis 1, all aus-tralopithecine humeri are closer to those ofapes than to those of humans. They sharewith apes relatively larger articular sur-faces (capitulum and trochlea) comparedwith both epicondyles, and a capitulummarkedly extended in inferior view. Apesand australopithecines also share a deeptrochlea, a salient lateral anterior trochlearcrest, and a salient lateral epicondyle.These features may have a functional mean-ing in relation to the use of forelimb in ar-boreal activities, such as suspension orclimbing, largely described in the literature

Fig. 3. Principal components analysis of superimposed landmarks for axis 3 (9.6%) and axis 4 (7.2%).Plots of individuals and extreme deformations are associated with each axis. 1, AL 288-1; 2, AL 137-48;3, TM 1517; 4, STW 431; 5, KNM-KP 271; 6, KNM-ER 739. Convex hulls are depicted for the maintaxonomic groups.

PCA OF DISTAL HUMERAL SHAPE 483

since the 1980s (Senut, 1981a,b; Stern andSusman, 1983; Susman et al., 1984; Schmid,1983; Senut and Tardieu, 1985; Coppensand Senut, 1991). The presence of a salientlateral trochlear crest (not so well developedas in Gorilla and Pan in my analysis) isbelieved to prevent the dislocation of thejoint during arboreal locomotion. Thegreater extension of the capitulum onto theposterior aspect of the epiphysis could allowa better extension of the elbow. The salienceof the lateral epicondyle would suggest pow-erful extensor muscles of the hand and thedigits.

Concerning modern apes, the morpholog-ical differences which enable discriminationof the three species are minor (Fig. 3; plots 3and 4), but it nevertheless appears possibleto accurately sort the three taxa of large-bodied apes (Pan paniscus, Pan troglodytes,and Gorilla gorilla) on the basis of the vari-ation of articular elements assessed on plots3 and 4 (Fig. 3). The results show that partof the shape differences among African apesare size-dependent (Table 3), and that thesedifferences mainly concern the articularsurfaces (proportions of the capitulum andthe trochlea). Both species of Pan present amassive trochlea and a well-developed ca-pitulum. Gorilla exhibits a large trochleawith a small capitulum.

To what can variation in shapebe attributed?

Most shape variations among all austra-lopithecines can be described by an allomet-ric effect, as the large degree of size differ-ences among fossil hominids appears aslarge as that observed between male andfemale gorillas. The correlation between co-

ordinates of each fossil on axis 2 and thecentroid size (r 5 20.957, P , 0.005, Table3) is the most significant, but only amongfossil hominids. These size-dependent fea-tures are a flat trochlea with flat anterolat-eral margins and a medial epicondyle whichis more anteriorly projected. These charac-teristics appear more and more pronouncedin AL 288-1, AL 137-48, TM 1517, STW 431,KNM-KP 271, and KNM-ER 739 (Table 2).

According to the distribution of the entiresample (both modern and fossil clusters)into axes 1 and 3 and centroid sizes, it ap-pears evident that the variations betweenthe different groups predominantly describeshape differences. However, a part of theseshape differences present an allometric ef-fect. The correlations between shape andsize (centroid size) are r 5 0.488, P , 0.05for axis 1, and r 5 0.462, P , 0.05 for axis 3(Table 3). These size-related features con-cern first the relative proportions betweenarticular surfaces (trochlea and capitulum)and epicondyles, and secondly, the relativeproportions between the trochlea and thecapitulum. Concerning this last character-istic (axis 3), the fossils are closer to Homo,with a positive allometry, than to Gorillaand Pan, characterized by a negative allom-etry.

Affinities of KNM-KP 271

With regard to the variation expressed byall specimens, especially as illustrated inthe first PCA plot (Fig. 2), the results do notemphasize a particular affinity betweenKNM-KP 271 and modern Homo, as previ-ously assessed by Lague and Jungers(1996). Moreover, it is interesting to notethat the features (a relatively large and

TABLE 2. Size parameters of the humeral epiphysis (logarithm of the centroid size)1

Species Sex N x SD MIN MAX

Modern Homo 31 M, 42 F 73 2.682 0.608 2.279 3.264Pan paniscus 9 M, 9 F 18 2.630 0.205 1.988 3.044Pan troglodytes 10 M, 3 F 22 2.653 0.286 2.324 3.323Gorilla gorilla 12 M, 13 F 26 3.908 0.780 3.169 5.090AL 288-1 2.044AL 137-48 2.391TM 1517 2.559STW 431 2.812KNM-KP 271 2.818KNM-ER 739 3.2531 M, male; F, female; N, effective; x, mean; SD, standard deviation; MIN, minimum; MAX, maximum.

484 A.-M. BACON

gracile trochlea, and a capitulum less ex-tended distally than in the other hominids)on which the Homo-like resemblance wasbased, appear here highly variable in Homoas they are significantly related to size (Ta-ble 3; correlation between axis 3 and cen-troid size in Homo, r 5 0.246, P , 0.05).

Among fossil hominids, KNM-KP 271 dif-fers also from AL 288-1 along axis 3 by thevariation of the contour of the articular ele-ments (capitulum and trochlea) (Fig. 3). Inthis respect, AL 288-1 clearly presentschimp-like similarities, whereas KNM-KP271 possesses Gorilla-like similarities (thepresence of a small capitulum combinedwith a mediolaterally large and a relativelygracile trochlea). However, these differencesare weak and the Kanapoi humerus appearscloser to other australopithecines than toany modern group.

Differentiation within australopithecines

Axis 4 emphasizes two groups: AL 288-1and AL 137-48 (Fig. 3, axis 4) appear mor-phologically distant from all other fossilhominids, but the differences appear to beminor with respect to the ranges of varia-tion of modern Hominoids. The distance ob-served between the two specimens of Hadaris compatible with intraspecific variation.AL 288-1 and AL 137-48, despite great vari-ation, appear closer to Pan paniscus in size(Table 2) and shape (Fig. 3).

In an attempt to differentiate distinctgroups within australopithecines, only theplot of axes 3 and 4 (Fig. 3) permits theisolation of KNM-ER 739 and TM 1517, to-gether with STW 431, from the other aus-tralopithecines. At the moment, Australo-pithecus africanus presents the closestaffinity with the alleged “robust” specimens.

However, taking into account the lowamount of variance explained by these axes,the separation of “robust” 1 A. africanusspecimens does not appear convincing.

CONCLUSIONS

In search of human origins, the literaturehas often put forward the Homo-like affinityof KNM-KP 271 (Patterson and Howells,1967; Day, 1978; Senut, 1979, 1981a,b; Se-nut and Tardieu, 1985; Leakey et al., 1995,1998) in comparison with the other austra-lopithecines, especially A. afarensis. On thebasis of the morphometric approach of thedistal humeral extremity, the results do notshow close resemblance between KNM-KP271 and Homo. Some features, however,that have been suggested to reveal humanaffinities of the Kanapoi humerus are notpresent in distal view (such as the salienceand the position of the lateral epicondylerelative to the capitulum in anterior view,the placement of the greatest anteroposte-rior diameter of the distal shaft (Pattersonand Howells, 1967; Senut and Tardieu,1985), and the presence of a marked mediananterior capsular ligament tubercle (Leakeyet al., 1995). In KNM-KP 271, a compara-tively mediolaterally large and anteroposte-riorly gracile trochlea, and a distally lessextended capitulum, were considered to bekey features for suggesting a closer resem-blance to Homo rather than to chimpanzees.However, taking into account here the vari-ation of humeral shape as a whole, no affin-ity with Homo emerges clearly; the analysisparticularly shows how large the size-de-pendent variation of these features is inHomo, larger than that seen in apes on mostaxes. Thus, the resemblance betweenKNM-KP 271 and Homo does not appear

TABLE 3. Correlation between size (log of the centroid size) and components of the first four axes of PCA foreach modern species and fossil hominids

Species Axis 1 Axis 2 Axis 3 Axis 4

Fossil hominids (n 5 6) 0.314 20.957** 0.594 0.516Modern Homo (n 5 73) 0.155 20.192 0.246* 0.022Pan paniscus (n 5 20) 0.355 0.076 20.330 20.139Pan troglodytes (n 5 22) 0.057 20.100 20.366 20.150Gorilla gorilla (n 5 26) 0.326 0.111 20.087 20.282All specimens (n 5 147) 0.488* 20.103 0.462* 20.117

* P , 0.05.** P , 0.005.

PCA OF DISTAL HUMERAL SHAPE 485

sufficient to support a privileged phyleticrelation with this genus.

Concerning systematics, more skeletalmaterial would be necessary to specify thenature of the differences observed betweenthe hominid of Kanapoi and the other aus-tralopithecine specimens (i.e., specific or ge-neric?). We do not know the real variabilitywithin the different species of Australo-pithecus (aside from A. afarensis, we haveonly one specimen for each species). How-ever, with regard to the homogeneity ex-pressed by the six fossil humeri (plots 1 and2, Fig. 2), no convincing taxonomic separa-tion can be proposed. The magnitude of dif-ferences observed between TM 1517,KNM-ER 739, STW 431, AL 288-1, AL 137-48, and KNM-KP 271 appears as minor asthat observed in the unique genus Homo.Thus, the results of this study support thoseof Leakey et al. (1995, 1998), who consid-ered KNM-KP 271 as belonging with otherelements discovered in Kanapoi in Kenya tothe genus Australopithecus, despite themorphologic arguments of Senut (1981b)and Senut and Tardieu (1985). Lague andJungers (1996) arrived previously at thesame conclusions with canonical variatesanalyses (CVA) of modern and fossil homi-noids. The 10 fossil humeri included in theiranalysis are more similar to each other thanthey are to any modern group. The maindifference is that, in the analysis of theseauthors, fossils are close to Pan troglodytes(axis 1 of the CVA, their p. 418), while inthis present analysis (axis 1 of the PCA, Fig.2), fossils are close to apes (both Pan andGorilla).

It must also be emphazised that there isno affinity with Australopithecus afarensis,a result which agrees with that previouslypointed out by Lague and Jungers (1996). Inan attempt to distinguish AL 288-1 fromKNM-KP 271, we can only conclude that theformer appears to be somewhat more“chimp-like,” wheareas the second is more“gorilla-like” (axis 3, Fig. 3). Our resultsshow that these shape variations amongapes and among the two fossil specimensare highly size-related and do not justifysome functional and thus taxonomic distinc-tion.

It can be noted that the features used bySenut and Tardieu (1985) to distinguishKNM-ER 739 in a morphologic and func-tional subgroup with KNM-ER 1504 andKNM-ER 3735 (i.e., the presence of an ar-ticular surface not very much different fromthe modern human one; that of a lateraltrochlear crest poorly salient and a lateralepicondyle which is strongly laterally sa-lient) do not appear to be as pertinent inthis morphometric approach, as they arehighly related to size parameters among allaustralopithecines (axis 2; Fig. 2), especiallythe two latter features. Neither “human-like” nor “ape-like” affinities can be accu-rately extracted for KNM-ER 739 and TM1517. These specimens cannot be separatedfrom any other fossils, both in size and mor-phometric profile.

ACKNOWLEDGMENTS

The author thanks Dr. W. Van Neer (Mu-see Royal de l’Afrique Centrale in Tervuren)for the study of great apes, Dr. J.L. Scheuer(Royal Free Hospital School of Medicine inLondon) for the study of the human popula-tion of St. Brydes, Pr. Tobias and Dr. Thack-eray for the study of originals of hominids inSouth Africa (this visit was financed by theFoundation Singer Polignac), and Pr. A.Langaney (Musee de l’Homme, MuseumNational d’Histoire Naturelle in Paris) forhis authorization to study casts of hominids.Thanks are also due to Pr. Yves Coppens forhis help and support, to M. Baylac, C.Berge, and M. Pickford for their suggestionsand corrections, and Daniele Fouchier forthe realization of the drawings. This studyis a contribution to the “Groupe de travailMorphometrie” of the Museum Nationald’Histoire Naturelle in Paris.

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