On the squamosal suture of KNM-WT 17000.

The extensive overlap of the temporal squama on the parietal in KNM-WT 17000 is restricted to a narrow segment of the arc of the squamosal suture. It appears as a long, narrow, posterosuperior extension onto the calvarial wall. The long axis of this extended strip is aligned with what appears to be the most hypertrophied section of the temporalis muscle fan. The substantial differences between the squamosal suture and associated masticatory elements of KNM-WT 17000 and those of Australopithecus boisei provide an opportunity to evaluate the various forces molding the anatomy of the squamosal suture of A. boisei. It is suggested that the extreme flare of the zygomatic arches in the latter accounts for these differences.     

Cranium of a juvenile Australopithecus boisei from the lower Omo Basin,Ethiopia

A partial cranium of a juvenile Australopithecus boisei, recovered from the Shungura Formation in the lower Omo basin, southern Ethiopia, and dated at 2.1 m.y. B.P. , is described anatomically and compared to young and adult australopithecines, modern Homo sapiens, chimpanzees, and gorillas. A resemblance to the gracile Australopithecus is observed but is attributed mainly to the generalized appearance of the Omo specimen resulting from its young individual age. An attempt is made to reconstruct part of the ontogenetic process of A. boisei. This process is compared to the developmental changes exhibited by the African great apes and modern man and is found to combine characteristics of both.     

Functional implications of squamosal suture size in paranthropus boisei

It has been hypothesized that the extensively overlapping temporal and parietal bones of the squamosal sutures in Paranthropus boisei are adaptations for withstanding loads associated with feeding. Finite element analysis (FEA) was used to investigate the biomechanical effects of suture size (i.e., the area of overlap between the temporal and parietal bones) on stress, strain energy, and strain ratio in the squamosal sutures of Pan troglodytes and P. boisei (specimen OH 5) during biting. Finite element models (FEMs) of OH 5 and a P. troglodytes cranium were constructed from CT scans. These models contain sutures that approximate the actual suture sizes preserved in both crania. The FEM of Pan was then modified to create two additional FEMs with squamosal sutures that are 50% smaller and 25% larger than those in the original model. Comparisons among the models test the effect of suture size on the structural integrity of the squamosal suture as the temporal squama and parietal bone move relative to each other during simulated premolar biting. Results indicate that with increasing suture size there is a decreased risk of suture failure, and that maximum stress values in the OH 5 suture were favorable compared to values in the Pan model with the normal suture size. Strain ratios suggest that shear is an important strain regime in the squamosal suture. This study is consistent with the hypothesis that larger sutures help reduce the likelihood of suture failure under high biting loads. Am J Phys Anthropol 153:260–268, 2014. © 2013 Wiley Periodicals, Inc.     

Relationship of squamosal suture to asterion on external skull surfaces versus endocasts of pongids: Implications for Hadar early hominid AL 162-28

The relationship between the squamosal suture and asterion was quantified in 15 hemispheres of eight chimpanzee endocasts that were aligned in the conventional lateral view (i.e., with frontal pole [FP]–occipital pole [OP] horizontal). Using a three-dimensional digitizer, x, y, and z coordinates were collected for the highest and lowest points of the squamosal suture, and the most rostral point of the suture approximate to the coronal suture. Our results were compared to a similar study of the squamosal suture on the external surfaces of chimpanzee skulls that were oriented in the Frankfurt horizontal (Holloway and Shapiro, 1992). The relationship between the squamosal suture and asterion differs markedly between the outsides of skulls and endocasts. Whereas the squamosal suture is very rarely below asterion on the external skull, we found that most of the squamosal suture is located inferior to asterion on endocasts. We also found that the squamosal suture courses approximately 2.0 mm lower on the right side than the left. (An asymmetry of the same magnitude was reported for the external skull but, curiously, in the opposite direction.) It may be that a lowered right squamosal endosuture on chimpanzee endocasts is associated with earlier closure on that side. The discrepancy in results for the external skull versus endocast is partially attributable to orienting chimpanzee skulls in the Frankfurt horizontal, which usually results in the endocasts being tilted so that FP is above OP, i.e., FP-OP is not parallel with the Frankfurt horizontal. Falk's (1985) orientation of the early hominid endocast from Hadar (AL 162-28) is consistent with data determined from endocasts of chimpanzees. © 1994 Wiley-Liss, Inc.     

Craniodental variation in Paranthropus boisei: a developmental and functional perspective

What levels and patterns of craniodental variation among a fossil hypodigm are necessary to reject the null hypothesis that only a single species is sampled? We suggest how developmental and functional criteria can be used to predict where in the skeleton of fossil hominins we should expect more, or less, within-species variation. We present and test three hypotheses about the factors contributing to craniodental variation in extant primate taxa, and then apply these results to the interpretation of the P. boisei hypodigm. Within the comparative samples of extant Homo, Pan, Gorilla, Pongo, and Colobus, variables from the cranial base, neurocranium, and face that are not subject to high magnitudes of strain have consistently lower levels of intraspecific variation than variables from regions of the face subject to high levels of strain. Dental size variables are intermediate in terms of their reliability. P. boisei is found to have a low degree of variability relative to extant primates for variables shown to be generally useful for testing taxonomic hypotheses. Contrary to the claims of Suwa et al. ([1997] Nature 389:489-492), the recently discovered material from Konso falls within the range of variation of the "pre-Konso" hypodigm of P. boisei for available conventional metrical variables. Those aspects of the Konso material that appear to extend the range of the P. boisei hypodigm involve regions of the skull predicted to be prone to high levels of within-species variation. The approach used in this study focuses on craniodental data, but it is applicable to other regions of the skeleton.     

Relationship of squamosal suture to asterion in pongids (Pan): relevance to early hominid brain evolution.

Based on 244 measurements of the relationship of the squamosal suture to the landmark asterion in 49 chimpanzee skulls, it is shown that in the normal lateral view the squamosal suture is very rarely inferior to asterion. In hominid crania, the squamosal suture is always well superior to asterion. Even in Pan, that part of the squamosal suture most homologous with the remnant found on the Hadar AL 162-28 Australopithecus afarensis hominid cranial fragment is very rarely inferior to asterion. Such variability suggests that Falk's (Nature 313:45-47, 1985) orientation of the Hadar specimen is incorrect; she places asterion superior to the position of the squamosal suture if projected endocranially. The implication for the brain endocast is that, however the fragment is oriented, the posterior aspect of the intraparietal (IP) sulcus is in a very posterior position relative to any chimpanzee brain. The distance from the posterior aspect of IP to occipital pole is twice as great in chimpanzee brain casts than on the Hadar AL 162-28 endocast, even though the chimpanzee brain casts are smaller in overall size. This suggests that brain reorganization, at least as exemplified as a reduction in primary visual striate cortex (area 17 of Brodmann), occurred early in hominid evolution, prior to any major brain expansion.     

The Evolution of Zinjanthropus boisei

Many people assume that OH 5, the type specimen of Paranthropus boisei, collected in 1959, was the first evidence of that taxon to be found, but OH 3, recovered in 1955, predated the discovery of OH 5 by four years. Thus, Paranthropus boisei recently celebrated the equivalent of its fiftieth birthday. This review marks that milestone by examining the way our understanding of this taxon has changed during its fifty, or so, year history.     

Testing the taxonomic integrity of Paranthropus boisei sensu stricto

The craniodental hypodigm of Paranthropus boisei sensu stricto is morphologically distinctive, but it has been suggested that the substantial variation in mandibular and dental size in that hypodigm may exceed that which is reasonable to subsume within a single hominin species. In this study, Fligner and Killeen, coefficient of variation (CV)-based and average taxonomic distance (ATD)-based bootstrap tests, were used to compare variation in size and shape of the mandibular corpus remains attributed to P. boisei s.s. with the variation observed in samples of great apes and modern humans. The degree of size variation in the P. boisei s.s. mandibular hypodigm is never observed in human and chimpanzee samples, is rare in gorillas, but is not uncommon in orangutans. However, the shape variation in the fossil group is comparable to the variation in the extant reference groups. Although the size variation in P. boisei s.s. is substantial, it is exaggerated by the effects of taphonomy. The small mandibles are more often abraded, whereas the large mandibles are more likely to have been infiltrated with matrix. On the basis of the results of this investigation of the mandibular corpus, there are no grounds for rejecting the "single-species" hypothesis for P. boisei s.s. When Sokal and Braumann's adjusted CV values were used to predict the index of sexual dimorphism (ISD) for the P. boisei s.s., despite the substantial geological time embraced by the mandibular corpus hypodigm, the predicted value of lnISD, when corrected for taphonomic factors, is comparable to the sexual dimorphism observed within Gorilla.     

The gait of Australopithecus

A biomechanical analysis of the pelvic and femoral samples available for Australopithecus is presented. No feature of these samples was found to distinguish their gait pattern from that of modern man or to differ in the two presently recognized allomorphs of Australopithecus. Morphological differences between Australopithecus and modern man appear to be the result of different degrees of encephalization rather than any difference in locomotor adaptation.     

The capitate of Australopithecus afarensis and A. africanus

The capitates of Australopithecus afarensis (AL 288-lw and AL 333–40) and A. africanus (TM 1526) have the identical combination of modern pongid, modern hominid, and unique characteristics. These traits include the combination of a length that is proximodistally shortened (Homo sapiens-like), a facet for the second metacarpal that is distolaterally facing (unique), the reduced styloid process on the third metacarpal (pongidlike), a dorsally placed trapezoid facet (pongidlike), mediolaterally constricted metacarpal III facet (pongidlike), a prominent palmar beak (pongidlike), a single elongated facet for the second metacarpal (H. sapiens-like), a waisted neck (pongidlike), and a reduced amount of “cupping” in the third metacarpal facet (H. sapiens-like). In overall shape the bones are more like H. sapiens than other extant hominids, although they are uniquely different. The two A. afarensis capitates provide no evidence that there are two postcranial morphotypes at Hadar. Available evidence shows that A. afarensis and A. africanus are strikingly similar postcranially. The morphological differences between the capitate of Australopithecus and H. sapiens may relate to the retention of climbing ability and an absence of certain grip capabilities in these early hominids.     

The locomotor anatomy of Australopithecus afarensis

The postcranial skeleton of Australopithecus afarensis from the Hadar Formation, Ethiopia, and the footprints from the Laetoli Beds of northern Tanzania, are analyzed with the goal of determining (1) the extent to which this ancient hominid practiced forms of locomotion other than terrestrial bipedality, and (2) whether or not the terrestrial bipedalism of A. afarensis was notably different from that of modern humans. It is demonstrated that A. afarensis possessed anatomic characteristics that indicate a significant adaptation for movement in the trees. Other structural features point to a mode of terrestrial bipedality that involved less extension at the hip and knee than occurs in modern humans, and only limited transfer of weight onto the medial part of the ball of the foot, but such conclusions remain more tentative than that asserting substantive arboreality. A comparison of the specimens representing smaller individuals, presumably female, to those of larger individuals, presumably male, suggests sexual differences in locomotor behavior linked to marked size dimorphism. The males were probably less arboreal and engaged more frequently in terrestrial bipedalism. In our opinion, A. afarensis from Hadar is very close to what can be called a "missing link." We speculate that earlier representatives of the A. afarensis lineage will present not a combination of arboreal and bipedal traits, but rather the anatomy of a generalized ape.     

鄂西“南方古猿”和印尼早更新世若干人类化石

在鄂西发现的四枚臼齿化石曾被认为是南方古猿的。鄂西臼齿,从其齿冠尺寸和形状等来看,与非洲的有关材料对比,更接近人属成员的;与印尼早更新世有关的化石对比,与魁人等的很相似。直立人牙齿的演化趋势和变异性表明:鄂西臼齿以及印尼早更新世人类下颌骨化石更大的可能是代表一类时代较早的直立人。     

Evolution of the mandibular third premolar crown in early Australopithecus

The Pliocene hominins Australopithecus anamensis and Australopithecus afarensis likely represent ancestor-descendent taxa—possibly an anagenetic lineage—and capture significant change in the morphology of the canine and mandibular third premolar (P₃) crowns, dental elements that form the canine honing complex in nonhuman catarrhines. This study focuses on the P₃ crown, highlighting plesiomorphic features in A. anamensis. The A. afarensis P₃ crown, in contrast, is variable in its expression of apomorphic features that are characteristic of geologically younger hominins. Temporal variation characterizes each taxon as well. The A. anamensis P₃ from Allia Bay, Kenya expresses apomorphic character states, shared with A. afarensis, which are not seen in the older sample of A. anamensis P₃s from Kanapoi, Kenya, while spatiotemporal differences in shape exist within the A. afarensis hypodigm. The accumulation of derived features in A. afarensis results in an increased level of P₃ molarisation. P₃ molarisation did not evolve concurrent with postcanine megadontia and neither did the appearance of derived aspects of P₃ occlusal form coincide with the loss of canine honing in hominins, which is apparent prior to the origin of the genus Australopithecus. A. afarensis P₃ variation reveals the independence of shape, size, and occlusal form. The evolution of the P₃ crown in early Australopithecus bridges the wide morphological gap that exists between geologically younger hominins on the one hand and extant apes and Ardipithecus on the other.     

Dental metric assessment of the omo fossils: implications for the phylogenetic position of Australopithecus africanus

The discovery of Australopithecus afarensis has led to new interpretations of hominid phylogeny, some of which reject A. africanus as an ancestor of Homo. Analysis of buccolingual tooth crown dimensions in australopithecines and Homo species by Johanson and White (Science 202:321-330, 1979) revealed that the South African gracile australopithecines are intermediate in size between Laetoli/hadar hominids and South African robust hominids. Homo, on the other hand, displays dimensions similar to those of A. afarensis and smaller than those of other australopithecines. These authors conclude, therefore, that A. africanus is derived in the direction of A. robustus and is not an ancestor of the Homo clade. However, there is a considerable time gap (ca. 800,000 years) between the Laetoli/Hadar specimens and the earliest Homo specimens; "gracile" hominids from Omo fit into this chronological gap and are from the same geographic area. Because the early specimens at Omo have been designated A. afarensis and the later specimens classified as Homo habilis, Omo offers a unique opportunity to test hypotheses concerning hominid evolution, especially regarding the phylogenetic status of A. africanus. Comparisons of mean cheek teeth breadths disclosed the significant (P less than or equal to 0.05) differences between the Omo sample and the Laetoli/Hadar fossils (P4, M2, and M3), the Homo fossils (P3, P4, M1, M2, and M1), and A. africanus (M3). Of the several possible interpretations of these data, it appears that the high degree of similarity between the Omo sample and the South African gracile australopithecine material warrants considering the two as geographical variants of A. africanus. The geographic, chronologic, and metric attributes of the Omo sample argue for its lineal affinity with A. afarensis and Homo. In conclusion, a consideration of hominid postcanine dental metrics provides no basis for removing A. africanus from the ancestry of the Homo lineage.