Sagittal Cresting in the South African Australopithecines

MILFORD H. WOLPOFF Department of Anthropology, University of Michigan, Ann Arbor, Michigan, 481 04

KEY WORDS Australopithecine . Sagittal cresting.

ABSTRACT The evidence for sagittal cresting, and more generally the position of the temporal lines is reviewed in the South African australopithecine sample. The position of the lines is dependent on both the allometric relation of the masticatory apparatus to cranial size and on individual variation. In the Swartkrans specimens, with generally bigger body size, the influence of allometry predomi- nates, actually overshadowing the influence of individual variation. At Sterkfon- tein and Makapansgat with generally smaller body size and a resulting smaller allometric ratio, individual variation has a greater influence. Of the eleven adult South African specimens, the four largest are crested. The one smaller crested specimen comes from Sterkfontein. The crested Makapan specimen is interme- diate in size. The pattern of australopithecine cresting is somewhat different from other hominoids, and is part of a total morphological pattern suggesting adaptation to a diet requiring powerful crushing during mastication.

Sagittal crests in hominoids are com- bres of m. temporalis first come together pound crests caused by the pull of both posteriorly in many primates, and that the temporalis muscles when they meet at the sagittal crest first forms in the posterior midline of the cranium. Functionally, the region, often in conjunction with a com- crest provides additional area for the at- pound temporahuchal crest. This does not tachment of m. temporalis when the area seem to be true in australopithecines where provided by the external cranial surface is the temporal lines first meet at bregma or insufficient. anterior to it, and the compound or inter- Formation of a sagittal crest is under the mediate temporal/nuchal crest, when it oc- direct control of the superior fascial attach- curs, is only along the lateral third of the ment of m. temporalis, and does not nec- nuchal crest (Robinson, '58; Tobias, '67). essarily depend on the meeting of two This indicates a relatively greater develop- simple temporal crests. If the two superior ment of the anterior fibers of m. temporalis. fascial attachments of m. temporalis meet This anterior development also occurs in at the midline, the fasciae run together to H. sapiens where the closest approach of the underlying bone, and a two layered the temporal lines in crania with high lines fibrous septum between the muscles is occurs in the region of bregma (Riesenfeld, formed (Scott, '54). The resulting osteo- '55). genic activity leads to ossification extend- There are two variables which systemati- ing into this septum, producing a sagittal cally influence the relation of temporalis crest. Ossification proceeds along the union size, and area available for attachment of the fascia and the outer layer of the The first is the allometric relation between periosteum, and the resulting crest consists the size of the masticatory apparatus and of two laminae which later fuse together. the size of the cranium. As Huxley ('32) The cresting process is the same for all noted for baboons, increase of body size in hominoids. However, the position of the the same, or even very similar, species leads crest when it first forms, and its anterior to far greater differences in the mastica- and posterior extension, depend on the rel- tory apparatus than in the size of the ative development of the anterior and pos- cranium, resulting in a disproportionate terior fibers of m. temporalis. Zuckerman ('66) has shown that the fi- 1 This research was supported by NSF grant (25.33035.

AM. J. PHYS.ANTHROP., 40. 397408 397 398 MILFORD H. WOLPOFF increase in the jaws and supporting mascu- than the temporal lines at lambda of OH 5 lature. The same relation can be seen in and ER 406 (Tobias, '67; Leakey, Mungai, comparing chimpanzees and gorillas. The and Walker, '71), making it likely that summed posterior tooth area for gorillas is MLD 1, too, had a sagittal crest. However, more than double that of chimpanzees there are at least 12 distinct Wormian while the average cranial capacity is less bones in the vicinity of lambda on both the than double. The effect of this allometric lambdoidal and sagittal sutures, The lamb- component is to decrease the relative area doidal suture is clear of Wormian bones in available for the attachment of m. tem- the vicinity of asterion and for about 30 poralis with increasing body size. The sec- mm medially. For lambda, Dart picked the ond variable influencing the relative at- point furthest posterior on the sagittal tachment area available on the cranium is suture anterior to the Wormian bone de- individual variation resulting from both velopment. Dart's definition makes the genetic and environmental influences, with ratio of lambda-inion to inion-opisthion the latter especially acting on the size and chords 55/37, an unusually high ratio for robustness of m. temporalis. These var- an australopithecine. This point cannot iables are not mutually exclusive. possibly be lambda, as it would put the The purpose of this paper is to review inferior limb of the parietal branch of the the data concerned with the position of the middle meningeal artery on the occipital. temporal line and sagittal cresting in the The lambdoidal suture can be clearly traced large South African australopithecine sam- to the sagittal suture internally, bordering ple now available for study. The point of the fossa for the occipital pole of the cer- this review is twofold: first to determine ebrum. Consequently, lambda can be un- the interaction of the allometry and indi- ambiguously defined internally, and the vidual variation components in temporal corresponding point can be defined on the line height, and compare these with other external surface. I believe this is the most primate models; and second to reconstruct appropriate definition of lambda. No su- the function of m. temporalis suggested by tures cross at this external point, 18.5 mm the australopithecine cresting pattern. posterior to the point defined by Dart. Using The terminology used here follows that it, the chord ratio of lambda-inion to inion- suggested by Robinson ('58). A simple crest, opisthion is about 39/37, much more like or ridge, is a raised area or elevated line the other australopithecine specimens (To- marking the periphery of a muscle not bias, '67; 13). The parietals extend for 34 closely bordered by another muscle. Thus, mm anterior to lambda. At the most ante- m. temporalis forms a crest where it bor- rior point, the temporal lines are 5 mm ders the temporal fossa and for the extent apart. At 34 mm anterior to lambda on that it parallels the superior orbital mar- OH 5, the lines have already met, and on gin, but as it travels posteriorly it becomes ER 406, the lines have just come together. an unelevated line. A compound crest, such These are the only crested specimens that as the sagittal crest, occurs at the interface show the morphology of this region. How- of two muscle masses. Specimens are di- ever, the distance between the temporal vided into gracile and robust samples based lines at lambda is known for a number of on published taxonomic statements. The specimens. The 35 mm value for MLD 1 is gracile sample consists of specimens from greater than both OH 5 and ER 406. It is Sterkfontein (STS) and Makapan (MLD), far less than the distance for the uncrested and the robust sample consists of specimens specimens (table l), and less than the value from Swartkrans (SK). I have made all ob- which can be estimated for STS 71 where servations and measurements used in this the temporal lines meet at bregma. Since study on the original specimens. on the most anterior portion of MLD 1 the temporal lines are only 5 mm apart and THE SPECIMENS still converging, and because sagittal MLD I. The question of cresting in this cresting in the australopithecines is ante- specimen depends on the true position of rior, I concur with Robinson's judgment lambda. According to Dart ('48), the tem- ('58: 413-416) that the specimen probably poral lines come within 5 mm of each other had a sagittal crest. at lambda. This is actually closer together MLD 10. The specimen is a pair of AUSTRALOPITHECINE SAGITTAL CRESTING 399

TABLE 1

Temporril line position ciizd other compcircible crtrizinl mecisz~resoj the South Afiiccrn iizistrnlopitheciizes

~~ ~ Distance Minimum ap- between Gla- Gla- proach tem- Stephan- temporal Sagittal Biaster- bella bella Bregma Lambda poral lines ion breg- lines at crest to ionic bregma bregma lambda opisthion ma arc lambda bregma breadth arc chord arc arc

mm mnz mm mni inm mnz mm mnz mnz MLD 1 O? 35 87 79 MLD 10 20 47 1 MLD37138 70 35 48 80 87 71 STS 5 40 22 51 72 80 77 92 72 STS 25 25 14 73 81 STS 71 0 0 - 77 75 69 85 73 SK 27 74 40 100 71 SK 46 0 0 24 >72 2 106 SK 47 78 SK 48 0 0 29 78 75 SK 49 0 0 26 SK 54 69 35 105 70 86 SK 801847 48 1 33 3 70 1 85 3

1 Estimated by doubling the midline distance. 1 Position of glabelia reconstructed using SK 48 as a model. 3 Bregma determined by convergence of the sagittal and coronal sutures, both present several millimeters from the point. The determination was unambiguous. fused parietals and a fragment of occipital of suture closure and dental ageing indicate extending from a point somewhat posterior that suture closure in the South African to lambda anteriorly for 60 mm in front of sample follows the same general pattern lambda. There is no trace of the coronal which occurs in modern man. suture on the anterior edge. At the most STS 5. The specimen is a complete, anteriorly preserved point on the sagittal edentulous cranium (Broom, Robinson, suture, the temporal lines are 20 mm apart. and Schepers, '50). Although most of the They are asymmetric, the left being 9 mm outer bone table is lost, the temporal lines from the suture and the right 13 mm. In- are visible. There is no sagittal crest. The ternally, the sagittal suture is closed, al- specimen is adult, and judging by endo- though not fused. It is unlikely that the cranial suture closure at least in her (?) specimen had a sagittal crest, as it was ap- 30s. parently an aged adult at the time of its STS 17. The specimen (fig. 3) consists death. of a frontofacial fragment with a full pal- MLD 37/38. The specimen is an almost ate (Broom, et al., '50). The face extends complete calvaria without face (Dart, '62). past the midline at the base of the nasal A transverse break continues a little behind aperture, although it does not reach the the coronal suture on the left, crosses it midline superior to this area. An associated 12.5 mm left of bregma, and continues an- occipital fragment seems to include lamb- teriorly and medially. The temporal lines da. It is so crushed and fragmented that are clearly visible; the specimen did not no surface detail can be observed. Using have a sagittal crest. Eruption of M:< indi- the midline defined by the palate and nasal cates that the specimen is adult, although aperture, the position of the midline for the it appears that the right tooth was reduced remaining face was reconstructed. The and newly erupted because it is only slight- superior border of the orbit is broken at a ly worn while the left shows considerable point 10 mm lateral to the midline. At this wear. I do not believe, as Dart ('62) sug- point the temporal crest travels parallel gests, that the right tooth is a supernumer- with the superior orbital margin for its en- ary M4 because of the symmetry of the tire preserved extent, and it only begins to palate. The spheno-occipital synchonchro- turn posteriorly at the position of the medi- sis is closed but still clearly visible, corre- al break. The closest approach of the crest sponding to an age of 24-28 based on mod- to the superior orbital margin is 8.3 mm. A ern suture closure critera. My comparisons concave flatteniiig of the supraglabellar 400 MILFORD H. WOLPOFF area, such as that described by Tobias for the sagittal area of the frontal and pari- OH 5 as a frontal trigone (‘67; 104), is pre- etals of STS 17 is missing, what possible served for 12.5 mm lateral to the break, course could the lines take if they did not which is 10 mm from the midline. This form an anterior sagittal crest? The alter- general area may be compared with other native would suggest that the specimen had specimens both without (STS 5, ER 732) anterior fibers of m. temporalis better de- and with (SK 48, ER 406) crests. In STS 5, veloped than the robust specimens dis- the temporal line begins a gentle postero- cussed, and almost no posterior develop- medial arc as it leaves the superior border ment at all. In my view, it is probable that of the temporal fossa (temporal notch). STS 17 had a sagittal crest. M:’ is fully in The line never is as close to the midline as occlusion and worn, indicating the speci- 10 mm. ER 732, an East African specimen men is adult. without a sagittal crest (Leakey, Mungai, STS 25. The specimen is a calvaria and and Walker, ’72), has a frontal trigone, in- cranial base, extending from the occipital dicating that this morphology does not nec- to the supraorbital region. The specimen is essarily indicate sagittal cresting. In this lacking much surface detail, and parts of specimen, the temporal line begins to turn the base are still enclosed in matrix. The posteriorly 34 mm from the midline, some left temporal appears crushed somewhat lat- 7 mm after it has left the temporal fossa. erally. Although much of the outer bone The line does not come within 10 mm of the table is gone, the position of the temporal midline on the frontal. The frontal trigone lines can be determined. There is no sagit- extends 21 mm from the midline, and thus tal crest. is about the size of the trigone area in STS 71. The specimen (fig. 2) is an al- STS 17. The morphology of SK 48 much most complete cranium with much of the more closely approximates the condition in left side broken away. The base of the right STS 17. In fact, the temporal crest remains parietal is crushed downwards and some- more anterior and medial in the latter. Ten what laterally over the temporal. Broom millimeters from the midline, the temporal (Broom, et al., ’50) thought the back of the line is already midway in its posterior turn, skull was crushed downwards and some- and is some 28 mm behind the superior or- what anteriorly. I do not believe this is true. bital margin. The position morphologically There is no evidence of overlapping bone equivalent to 10 mm from the midline in in the sagittal plane which would result STS 17 is 23 mm from the midline in SK 48, from anterior crushing of the occipital re- where the line first begins its posterior gion. The cranial bone surface is complete turn. At this point it is 17 mm behind the and continuous from glabella to opisthion. superior orbital margin. Similarly in ER Thus, if the occipital region were crushed 406 the line is almost completely turned anteriorly, it must also be flexed in a down- posteriorly at a point 10 mm from the mid- wards direction. This is unlikely because line, and is 31 mm behind the superior the nuchal line, as preserved, is several orbital rim. It begins its posterior turn 27 millimeters above the Frankfort Horizontal. mm from the midline, when it is 14.4 mm While there is no sagittal crest, the tem- behind the orbit. Even if the midpoint esti- poral lines meet for a millimeter in the re- mate for STS 17 is off by 100% it still gion of bregma. At the midpoint of the closely matches the morphology for these orbit the line is 20 mm behind the superior two crested specimens. orbital margin, and is already angling There are two points to be considered. about 45 degrees away from the margin. First, sagittal cresting, or closest approach The right line continues to the rear of the of the temporal lines, in australopithecines cranium where it meets the nuchal line to is uniformly anterior, occurring at or an- form an apparent, although not raised, terior to bregma. Second, the temporal compound crest area at the posterior posi- crest in STS 17 parallels the orbit and the tion of the mastoid process, 39 mm behind line begins its posterior turn in a more porion. M” is fully in occlusion and worn. medial position for STS 17 than is the case STS 1006. The specimen (figs 4a,b) is for the two crested specimens discussed, a new juvenile frontofacial fragment dis- and far more medially than in the two un- covered in 1972, consisting of most of the crested specimens and STS 71. Although right portion of a face with a complete AUSTRALOPITHECINE SAGITTAL CRESTING 40 1 nasal aperture, and part of the frontal be- is otherwise complete to lambda. SK 46 is hind the right orbit. Much of the face is one of the two South African robust aus- lost anterior to a line perpendicular to the tralopithecine adults with a fairly complete base of the orbit, and the alveolar margin parietal. The parietal, especially in the pos- is broken away exposing roots above the terior portion, is crushed downwards and bifurcation. The posterior roots, present on medially, so that the region of porion is both sides, measure 13 mm X 12.6 mm on angled at 45" to and is 40 mm from the the right and probably belong to MI. On sagittal plane. The superior cranial surface the left side there is a palatine foramen is continuous to lambda, and arcs taken on just level with this root. The root anterior it should be accurate. A minimum recon- to this best matches the posterior root for struction of glabella was made by following dM2, rather than P4. Thus, the specimen the line of the supraorbital torus to the is likely between the age of Taung and the midline. This assumes no glabellar promi- age of SK 27 (8-10). It makes an interest- nence such as occurs on SK 48. If this ing comparison with these two specimens, region matches SK 48, glabella is further as 1006 is quite unlike Taung and rather anterior. The position of the coronal suture closely matches SK 27. The supraorbital and bregma was identified using a binocu- torus is well developed and set off from the lar microscope. As reconstructed, the gla- frontal bone by a supraorbital sulcus. The bella-bregma chord is 72 mm. There is a temporal line is medial on the frontal bone. well developed sagittal crest, beginning 24 It does not travel parallel with the superior mm in front of bregma and extending for orbital margin but rather angles medially about 45 mm posterior to bregma until it and posteriorly from the temporal notch in is broken off (Robinson, '58). M3 is in oc- a smooth arc. At the midpoint of the orbit clusion and well worn. the temporal line is 25.5 mm posterior to SK 47. The specimen is a very crushed the superior margin and 27 mm from the juvenile cranium (Broom and Robinson, midline. In all, this region is much like '52). The nuchal torus can be traced from SK 27. the mastoid process to inion. The temporal SK 27. The specimen is a very crushed line is well above it. M2 shows slight wear cranium (Broom and Robinson, '52). Most on the mesial cusps and P4 is barely beyond of the distortion is flattening, so that the the alveolar margin. The high temporal highest point on the cranium is about 75 line seen on the occipital portion of this mm above the lowest. M2 is unerupted and juvenile specimen makes it unlikely, al- rootless. The left 1' is in occlusion. The though not impossible, that it had a sagit- temporal lines are visible and not promi- tal crest. Tooth wear and eruption indicate nent. On the left side, the line meets the an age of 13-14. supramastoid crest just behind the mastoid SK 48. The specimen is one of the more area, some 25 mm anterior to asterion. The complete crania from Swartkrans, although line leaves the temporal notch and imme- there is much crushing and distortion diately arcs medially and posteriorly. The (Broom and Robinson, '52). The cranial superior cranial surface is distorted, but for surface is lost behind bregma, and the the regions discussed there is no overlap- posterior portion of the skull is mostly miss- ping of bone or matrix filled cracks. Accu- ing. The anterior distortion of the posterior rate chords cannot be taken but arcs are region is reflected in the base where the possible. The arc from the temporal line to foramen magnum is between the pterygoid bregma is 39 mm, which is about half the processes. A sagittal crest begins anterior distance from fmo (the fronto-zygomatic to bregma, identified with the use of a suture at the orbital border) to the midline. binocular microscope. At the midpoint of From the lateral orbital rim, the most me- the orbit, the temporal crests are still paral- dial position of the line is 24 mm. The age lel with the superior orbital margin. This of SK 27 is probably 8-10 years, based on is the usual case in robust specimens such tooth eruption and wear. as OH 5, ER 406, SK 79, and SK 52. MR is SK 46. The specimen (fig. 1) consists erupted and worn. of most of a somewhat distorted cranium SK 49. This very crushed and fragment- (Broom and Robinson, '52). The glabellar ed specimen was discussed in detail by region is missing, but the cranial surface Robinson ('58). A sagittal crest is present. 402 MILFORD H. WOLPOFF

Fig. 1 SK (Swartkrans) 46. The temporal ridge paral- Fig. 2 STS (Sterkfontein) 71. The tem- lels the orbit, bordering laterally the frontal trigone, and poral line arcs posteriomedially as it leaves then smoothly sweeps posteriorly as a line, converging the temporal notch (superior border of the with the opposite line to form a sagittal crest. temporal fossa), and meets the opposite line at bregma. There is neither a sagittal

Fig. 3 STS 17. The temporal ridge parallels the orbit to a more medial position than occurs in SK 46, and then arcs posteriorly with a strong Fig. 4 STS 1006. 4a (left) is anterior and 4b (right) lat- medial angle to the point where the eral. The temporal line of this juvenile specimen arcs pos- cranium is broken, about 10 mm from teriomedially from the temporal notch, reaching a position the midline. A frontal trigone is pres- on the preserved bone more medial than that of STS 5. ent, and it is likely that the specimen There is a strong supraorbital torus development and a was crested. Same scale as figure 2. supraorbital sulcus.

The crest begins about 26 mm anterior to extensive plastic distortion (Brain, '70). bregma. Ten millimeters anterior to lamb- The skull is folded along the coronal suture. da the crest is absent, and no trace of the Both parietals are present to the temporal temporal lines can be seen. The mesial border. The supraorbital torus is almost cusps of M3 are worn, indicating that the undeveloped but set off from the frontal by specimen is adult. a supraorbital sulcus. The temporal line, SK 54. The specimen is a juvenile cra- while not particularly medial, is well de- nium, complete from nasion to inion, with veloped and prominent. The line arcs pos- AUSTRALOPITHECINE SAGITTAL CRESTING 403 teriorly and medially from the temporal TABLE 2 notch. Just behind the notch it is 32 mm Szzc comparisons of SK 801847, the composite Swczrtkrtms crunium, with other South from the midline of the frontal. While it is Africnn austrnlopithecines not possible to age the specimen precisely, the open sutures and lack of supraorbital Mastoidale Auriculai A~rkular to (mm) point to point development indicate it was adolescent if prosthion g label1a to fmd 3 not juvenile. No sagittal crest occurs. mm mm SK 80/847. The specimen is a composite SK 801847 126 101 65 of SK 80 and 847 consisting of the face, SK 52 1 135 73 part of the frontal lateral to the midline, SK 48 110 81 and most of the temporal and sphenoid. The SK 46 > 148 116 2 86 STS 5 150 110 79 true position of temporal line on the fron- STS 71 >130 94 68 tofacial fragment is difficult to establish 1 These values are minimum since M3 is still in its because of a groove which angles quite crypt. medially from the superior border of the 2 Glabella is reconstructed following the morphology temporal fossa, or the temporal notch. A of SK 48. Frontomalaw orbitale, the orbital end of the fronto- binocular microscope was used to deter- zygomatic suture. mine the position of the less well developed line. The line leaves the temporal notch in suture is present several millimeters from a gentle arc. At its furthest posterior posi- the midline. By extending this suture to the tion on the fragment it is 18 mm from the midline, and extending the sagittal suture midline and 27.8 mm behind the superior forward, the position of bregma can be ac- orbital margin. At this point it is angled curately determined. The resulting bregma- about 90 degrees to the orbital margin, al- lambda chord cannot be greater than 75 though since the margin angles strongly mm, and is probably several millimeters anteriorly and medially, the line is still far less. This makes it a very small bone com- from parallel to the sagittal plane. Eight- pared with any of the other South African een millimeters from the midline in STS 5, specimens. The bregma-lambda arc is 85 the temporal line is already parallel with mm, slightly less than the value for SK 54, the sagittal plane. Originally I suggested although greater than SK 27. The only the specimen might have had a sagittal adult Swartkrans specimen for which this crest (Wolpoff, ’71a) because Tobias’ pub- arc can be taken, SK 46, has a value of lished measurements of supraorbital torus 106 mm. The corresponding arc on the SK length, taken “to the temporal crest or 1585 endocast, with a cranial capacity of line” (‘67: 104) suggested to me that the 530 cc (Holloway, ’72) is 91 mm. The arc line closely paralleled the superior orbital would be greater on the external cranial margin. Examination of the specimen re- surface. In all, SK 847e appears to be a vealed that this is not the case, and the very small parietal compared with the oth- lateral position of the line indicates that a er Swartkrans specimens. Some compari- crest is unlikely. Heavy wear on the third sons can be made between the size of the molar and fusion of the stylovaginal proc- composite cranium and other adult Swart- ess of the temporal suggest an advanced krans specimens. Tables 1 and 2 indicate age for the specimen, so lack of cresting that where such comparisons are possible, cannot be due to age. the composite skull is much smaller. The SK 847e. This is a piece of left parietal fact that the parietal and the cranium are including sagittal and lambdoidal suture separately much smaller when compared to found in the same block of breccia as the the other Swartkrans specimens, plus their frontofacial fragment (without the maxilla close proximity, make it likely that they SK 80) in close proximity to it. Proximity belong to the same individual. The position in the Transvaal caves does not necessarily of the temporal line on the resulting com- indicate that fragments belong to the same posite shows that no sagittal crest occurred. specimen. However, I believe it likely that Alternatively, if the parietals and compo- SK 847e goes with the frontofacial and tem- site cranium represent two separate indi- poral portions of the composite cranium. viduals, then both lack the sagittal crest. Although Clarke, Howell, and Brain (‘70) These would be the two smallest adult spec- did not find it, a small section of coronal imens at Swartkrans. 404 MILFORD H. WOLPOFF

DISCUSSION body size is much less, and the range is not The formation of a sagittal crest, and as extensive, cresting depends more on in- more generally the height of the temporal dividual variations in the relation of cra- lines, is dependent upon two factors: the nial size and temporalis size. This contrasts size of m. temporalis, and the amount of with gorillas where both variation in size, area available for its attachment on the and absolute size itself, is so great that al- cranium. These factors seem to covary in lometric changes in the relation of the gorillas, following the expected relation masticatory apparatus to cranial size actu- that brain size increases less rapidly than ally can hide individual variations in this the masticatory apparatus with increasing relation. That is, the allometric contribu- body size. Thus in a sample of over 200 tion, in accounting for a great deal of the specimens in the Hamann-Todd collection, observed variation, obscures the contribu- I have observed that the bigger specimens, tion of individual variation in cranial size regardless of sex, always have sagittal and the size of the masticatory apparatus crests as adults. On the other hand, in H. separately. In a sample of over 100 chim- sapiens neither the size of the masticatory panzees in the Hamann-Todd collection, I apparatus nor cranial capacity closely cor- observed that while sagittal cresting oc- relates with either body size or with each curred more often on larger than smaller other for the species as a whole. The var- individuals, the pattern was far from uni- iation in the masticatory requirements of form. Some cresting occurred in smaller different diets has led to extensive differ- individuals and many of the larger speci- ences in the development of the mastica- mens were uncrested. The pattern for gib- tory apparatus among numerous popula- bons reported by Holloway ('62) appears to tions (Hunt, '59; Scott, '57; Waugh, '37; be the same. Friel, '26). While variation within each These considerations give us three possi- population seems to have some dependence ble models which may apply to the austra- on body size, the variation between them lopithecines: great dependence on body does not. If cranial capacity is used as a size, some dependence on individual var- measure of the amount of area available iation, and great dependence on individual for the attachment of m. temporalis, then variation. The key factor is the relative im- this area also is poorly related to body size, portance of the allometric contribution to (Tobias, '70) if at all. Pakkenberg and Voigt the area available €or m. temporalis at- ('64), in a study relating brain weight to tac hment. body size in Danes, report regression co- Robinson ('58: 425) relates variation in efficients not significantly different from australopithecine crest formation to the zero when comparing brain and body height of the calvaria and the size of the weight. The regression of brain weight and jaws and teeth. This hypothesis is difficult body height shows some degree of depend- either to confirm or deny since no South ence. How little dependence is indicated by African specimen allows the measurement Schreider ('66) who reports correlations of of both cranial height and summed poste- brain weight and body height for 224 male rior tooth area, the best functional measure and 111 female samples as 0.26 and 0.31 of the masticatory apparatus (Wolpoff, respectively. Thus, this relationship is not '71b). In fact, cranial height cannot be particularly close. The combination of two taken for any South African robust austra- factors, each poorly if at all related to body lopithecine! Two gracile specimens with size, suggests the prediction that the dis- teeth can be measured for cranial height. tance between the temporal lines for a However, for STS 71 only M2 is measurable, mixed H. sapiens sample should be more or while for MLD 37/38 only M3, so these can- less independent of either body size or cra- not be directly compared. nial size. Evidence supporting this conten- It is not possible to relate cresting to tion can easily be compiled from data given body height. Only two South African spec- by Riesenfeld ('55). imens have related cranial and postcranial Chimpanzees provide a third model of skeletal material. For STS 7, the cranial cresting. The relations of m. temporalis material is a mandible while the TM 1517 and the masticatory apparatus is much like cranium is without frontal, parietals, or that of gorillas. However, because absolute occipital. AUSTRALOPITHECINE SAGITTAL CRESTING 405

This leaves only the possibility of trying TABLE 3 to relate the position of the temporal lines Size comparisons ofthe STS 17 face with the other to the size of the cranium. In the Swart- Sterkfontein fuces on craniu with temporal krans adult sample of four, the only spec- line position infonncition imen without a sagittal crest is the small- Height est in comparable cranial dimensions. This from alveo- seems to fit the gorilla model. The Swart- lar margin at M’IM3 to krans juveniles are more difficult to judge, the superi- since SK 54 cannot be aged. Interestingly, Outer or supraor- orbital Upper fa- Alveolar bital sur- SK 54 is a larger calvaria than SK 27, and breadth cia1 height height face the temporal lines are closer together. The ~~ mm mm mm mm problem in comparing the ages of these two STS 17 961 662 23.7 84.5 lies in the fact that while the larger size STSS 103 73.5 32.5 91 and more prominent lines of SK 54 argue STS71 931 77.0 28 87 for it being older, the less developed supra- 1 Estimated by doubling the midline distance. orbital torus could indicate that it is young- 2 Position of nasion reconstructed. er. Since both calvarial size and supraorbital development show great variation lines. Their position on the frontal is al- among the Swartkrans adults, no conclu- ready far more medial than the position sion can be drawn. of the lines in the corresponding area of In the gracile sample of seven adults, STS 5. It is possible that the adult would combining Sterkfontein and Makapansgat, have had a sagittal crest. This possibility two specimens are likely to have sagittal is enhanced by the correspondence of the crests, and the temporal lines meet at breg- temporal lines in this specimen to a ma in a third. One of the probably crested Swartkrans juvenile of similar age, SK 27. specimens, MLD 1, is larger than all other The gracile sample seems to follow the gracile crania in comparable measures. chimpanzee model of cresting. While the STS 71, the specimen for which the lines largest specimen has a crest, one of the meet at bregma, is larger than the remain- smallest also does. Thus, cresting seems to ing graciles in occipital measurements, respond to individual variation in the re- excepting the biasterionic breadth of MLD 1 lationship of cranial and masticatory appa- and MLD 37/38. On the other hand, it is ratus size. This presumably relates to the at the low end of the range in most dimen- smaller body size of the gracile australo- sions taken on the parietals and frontal. pithecines, reducing the allometric com- This suggests that it is the relatively small ponent of this relationship. Among the calvaria rather than a relatively large mas- uncrested graciles, there is no apparent ticatory apparatus which results in the pattern of relationship between most mea- high temporal lines. For STS 17, the second sures of cranial size and the height of the specimen that probably had a sagittal crest, temporal lines. The only measure that no calvarial measurements are possible. seems to covary uniformly with the distance Table 3 compares facial measurements between the temporal lines is the lambda- with STS 5 and 71. STS 17 is smaller than opisthion arc for four specimens. Specimens these in most dimensions, and in fact is one with greater arcs have closer lines. Inter- of the smallest faces at Sterkfontein. Small estingly, I have used the lambda-opisthion faces do not necessarily go with small cal- chord in regression equations to predict variae. For instance, some facial dimen- successfully cranial capacities in other sions of STS 71 are greater than those of hominid species (Wolpoff, ’71c). In sum, STS 5. Yet, STS 5 is larger in most calvari- the position of the temporal lines in the a1 dimensions, and has a greater cranial gracile sample can best be explained as a capacity (Holloway, ’70). However, since combination of allometric size changes and STS 17 was probably crested, one would individual variation in the relation of cra- expect a very small calvaria to go with the nial size and the masticatory apparatus. face. STS 71, with a smaller calvaria than Comparing the single uncrested adult STS 5, has closer temporal lines. The only Swartkrans specimen (SK 80/847) with the juvenile specimen for which information is gracile sample is of some interest. As tables available, STS 1006, has high temporal 1 and 2 indicate, the specimen is on the 406 MILFORD H. WOLPOFF small end of the gracile range in most In sum, the unique features in australo- cranial dimensions. One might expect a pithecine cresting are part of a total mor- mixture of the presence and absence of phological pattern adapted to generating cresting in small specimens as additional powerful horizontal forces through the en- specimens are recovered. tire molar-premolar row during mastica- The pattern of australopithecine cresting tion. The occurrence of this morphology is somewhat different than that of other suggests that hard objects made up an hominoids. Robinson (‘58) first pointed out important part of the australopithecine that cresting in the australopithecines diet. tended to be anterior, compared with the CONCLUSION pongids. Every known crest begins anterior to bregma and in the specimen where Sagittal cresting occurs in both gracile the lines only meet, they meet at bregma. and robust South African australopithecine The separate lamina of the crest fuses an- samples. The frequency difference between terior to bregma before the posterior seg- these samples, if significant, probably re- ment fuses. Tobias (’67) reported fusion of lates to the generally larger body size of the the anterior portion of the OH 5 crest, and robusts. The pattern of australopithecine the same anterior fusion occurs for ER 406. cresting indicates a larger anterior tem- In SK 48 and 46 the entire preserved crest poralis component which, in conjunction is fused, but in SK 49, dentally older than with the anterior position of the zygomatic OH 5, the anterior segment is not fused. process, is part of a total morphological pat- These data suggest that the anterior por- tern of adaptation to a diet including foods tion of the crest forms first, but also indi- which require powerful crushing during cates variation in the age of crest forma- mastication. tion. ACKNOWLEDGMENTS Because of the increased anterior component of m. temporalis, the temporal crest I am deeply indebted to C. K. Brain and parallels the superior orbital margin to a E. Voigt of the Transvaal Museum, P. V. far more medial position than is usually Tobias and A. R. Hughes of the Department the case in pongids (Tobias, ’67). I have ob- of Anatomy, University of the Witwaters- served that both the origin of the crest and rand, and M. D. Leakey, M. D. M. Leakey, the closest approach of the temporal lines and R. E. F. Leakey of the National Muse- in the uncrested specimens are uniformly ums of Kenya, Centre for Prehistory and anterior. Jolly (’70: 13) suggests that the Palaeontology, for permission to examine more anterior m. temporalis attachment the fossil hominid material in their posses- acts to bring the action of the muscle “al- sions, and for the help and encouragement most parallel to that of the masseters.” given to me during my visit. I am grateful Actually, in the larger specimens the ac- to the Cleveland Museum of Natural His- tion of’the masseters themselves is brought tory for permission to study the Hamann- forward by a very anterior position for the Todd collection. zygomatic process of the maxilla. I believe the main function of the anterior masseter LITERATURE CITED attachment and the strongly developed an- Brain, C. K. 1970 New finds at the Swartkrans australopithecine site. Nature, 225: 1112-1 119. terior component of m. temporalis is to Broom, R., and J. T. Robinson 1952 Swartkrans bring the resultant of these with the poste- ape-man. Transvaal Mus. (Pretoria) Mem., 6. rior fibers of m. temporalis, when it is used Broom, R., J. T. Robinson and G. W. H. Schepers contralaterally, through the anterior area 1950 Sterkfontein ape-man Plesianthropzis. Transvaal Mus. (Pretoria) Mern., 4. of the molar row. This would maximize the Broom, R., and G. W. H. Schepers 1946 The power available to the cheek teeth, and is South African fossil ape-men: The Australopi- likely adaptive to a dietary regime includ- thecinae. Transvaal Mus. (Pretoria) Mem., 2. ing hard objects. Consequently in the larg- Clarke, R. J., F. C. Howell and C. K. Brain 1970 er specimens, teeth in close proximity to More evidence of an advanced hominid at Swart- krans. Nature, 225: 1219-1222. the anterior portion of the molar row, such Dart, R. A. 1948 The Makapansgat proto-human as the fourth premolar, tend to be heavily Australopithecus prometheus. Am. J. Phys. molarized. Anthrop., 6: 259-281. AUSTRALOPITHECINE SAGITTAL CRESTING 407

1962 The Makapansgat pink breccia Robinson, J. T. 1958 Cranial cresting patterns australopithecine skull. Am. J. Phys. Anthrop., and their significance in the Hominoidea. Am. 20: 119-126. J. Phys. Anthrop., 16: 397428. Friel, S. 1926 An investigation into the relation Schreider, E. 1966 Brain weight correlations cal- of function and form. Brit. Dent. J., 47: 353-379. culated from original results of Paul Broca. Am. Holloway, R. L. 1962 A note on sagittal crest- J. Phys. Anthrop., 25: 153-158. ing. Am. J. Phys. Anthrop., 20: 527-530. Scott, J. H. 1954 The growth and function of the 1970 Australopithecine endocast (Taung muscles of mastication in relation to the devel- specimen, 1924): A new volume determination. opment of the facial skeleton and of the denti- Sci., 168: 96&968. tion. Am. J. Orthodont., 40: 429449. 1972 New australopithecine endocast, 1957 Muscle growth and function in rela- SK 1585, from Swartkrans, South Africa. Am. J. tion to skeletal morphology. Am. J. Phys. An- Phys. Anthrop., 37: 173-186. throp., 15: 197-234. Hunt, E. E. 1959 The continuing evolution of Tobias, P. V. 1967 Olduvai Gorge, Volume 11: modern man. Cold Spring Harbor Symp. Quant. The Cranium and Maxillary Dentition of Austrcc- Biol., 24 : 245-254. Zopithecus (Zinjanthropus) boisei. Cambridge Huxley, J. S. 1932 Problems of Relative Growth. University Press, London. Methuen, London. 1970 Brain-size, grey matter, and race Jolly, C. J. 1970 The seed-eaters: A new model -fact or fiction? Am. J. Phys. Anthrop., 32: of hominid differentiation based on a baboon 3-26. analogy. Man, 5: 1-26. Waugh, L. M. 1937 Influence of diet on the jaws Leakey, R. E. F., J. M. Mungai and A. C. Walker and face of the American Eskimo. J. Am. Dent. 1971 New australopithecines from East Rudolf, Assn., 24: 1640-1647. Kenya. Am. J. Phys. Anthrop., 35: 175-186. Wolpoff, M. H. 1971a Is the new composite cra- 1972 New australoDithecines from East nium from Swartkrans a small robust australo- Rudolf, Kenya (11). Am. J.-Phys. Anthrop.,-36: pithecine? Nature, 230: 398401. 2 35-2 52. 1971b A functional measure of tooth size. Pakkenberg, H., and J. Voigt 1964 Brain weight Southw. J. Anthrop., 27: 279-286. of the Danes. Acta Anat., 56: 297-307. 1971c Vertesszollos and the presapiens Riesenfeld, A. 1955 The variability of the tem- theory. Am. J. Phys. Anthrop., 35: 209-216. poral lines, its causes and effects. Am. J. Phys. Zuckerman, S. 1966 Myths and methods in Anthrop., 13: 599420. Anatomy. J. Roy. Col. Surg. Edinb., 11 : 87-1 14.

Note udded in proof: Recent experimental work indicates an additional factor that should be considered in the analysis of australopithecine cresting. Biomechanical analysis of the magnitude and direction of temporalis, pterygoid, and masseter muscles in modern man accurately predict measured tooth load, under the assumption that the joint reaction force in the mandibular fossa is minimized during molar loading. The force diagram leads to a set of three simultaneous equations which allow solution for the magnitude of temporalis and masseter force given the directions of these muscles and the magnitude of the tooth load. In the australopithecines, tooth load can be estimated using the proportional difference in summed posterior area compared with modern man. The average direction of temporalis is minimally the same as modern man, although I have suggested this component should be somewhat more anterior. The masseter direction can be estimated from the position of the zygomatic process of the maxilla. Four specimens were analyzed using these assumptions: STS 5 articulated with STS 52, SK 80 articulated with SK 15, SK 52 articulated with SK 23, and OH 5 articulated with the mandible reconstructed by R. Clarke. In modern man, the average ratio of temporalis to masseter force magnitude during molar loading is 1.1. In these australopithecine specimens the ratios were 1.8, 2.0, 2.1, 2.2 respectively. This variation stems from the more anterior placement of masseter, resulting in a greater posterior component of temporalis. Thus in the specimen with the most anterior masseter attachment, the expected force in masseter is about double that in modern man, while the temporalis force is about four times that of modern man. If the line of action for temporalis is more anteriorly directed, the expected posterior component will be even greater. In any event, the mag- 408 MILFORD H. WOLPOFF

nitude of temporalis varies with the flexion of the masseter angle. All other things being equal, specimens with a more anterior masseter attachment can be expected to have higher temporal lines and, if the cranium is small enough, a crest. Anterior temporalis development relates more closely to the force through the tooth row while posterior development is a function of both lateral force and the flexion of the masseter angle.