New first metatarsal (SKX 5017) from Swartkrans and the gait of Paranthropus robustus

A new complete hallucal metatarsal (SKX 5017) was recovered from the "lower bank" of Member 1 at Swartkrans (ca. 1.8 m.y. BP). The new metatarsal is attributed to Paranthropus robustus, the predominant hominid found in Member 1 (greater than 95% of hominid individuals). SKX 5017 is similar to Olduvai Hominid 8-H from bed I, Olduvai (ca. 1.76 m.y. BP), and both resemble humans most closely among extant hominoids. The base, shaft, and head of SKX 5017 suggest human-like foot posture and a human-like range of extension (= dorsiflexion) at the hallucal metatarsophalangeal joint, while at the same time the distal articular surface indicates that a human-like toe-off mechanism was absent in Paranthropus. The fossil evidence suggests that Homo habilis and Paranthropus may have attained a similar grade of bipedality at roughly 1.8 m.y. BP.     

A review of early Homo in southern Africa focusing on cranial, mandibular and dental remains, with the description of a new species (Homo gautengensis sp. nov.)

The southern African sample of early Homo is playing an increasingly important role in understanding the origins, diversity and adaptations of the human genus. Yet, the affinities and classification of these remains continue to be in a state of flux. The southern African sample derives from five karstic palaeocave localities and represents more than one-third of the total African sample for this group; sampling an even wider range of anatomical regions than the eastern African collection. Morphological and phenetic comparisons of southern African specimens covering dental, mandibular and cranial remains demonstrate this sample to contain a species distinct from known early Homo taxa. The new species Homo gautengensis sp. nov. is described herein: type specimen Stw 53; Paratypes SE 255, SE 1508, Stw 19b/33, Stw 75-79, Stw 80, Stw 84, Stw 151, SK 15, SK 27, SK 45, SK 847, SKX 257/258, SKX 267/268, SKX 339, SKX 610, SKW 3114 and DNH 70. H. gautengensis is identified from fossils recovered at three palaeocave localities with current best ages spanning ∼2.0 to 1.26-0.82 million years BP. Thus, H. gautengensis is probably the earliest recognised species in the human genus and its longevity is apparently well in excess of H. habilis.     

Hominin first metatarsals (SKX 5017 and SK 1813) from Swartkrans: a morphometric analysis.

Two hominin metatarsals from Swartkrans, SKX 5017 and SK 1813, have been reported by Susman and Brain [1988. New first metatarsal (SKX 5017) from Swartkrans and the gait of Paranthropus robustus. Am. J. Phys. Anthropol. 79, 451-454] and Susman and de Ruiter [2004. New hominin first metatarsal (SK 1813) from Swartkrans. J. Hum. Evol. 47, 171-181]. They found these bones to have both primitive and derived traits indicating that, while being bipedal, these hominines had a unique toe-off mechanism. We have undertaken additional multivariate morphometric analyses, comparing the fossils to the first metatarsals of modern humans and extant apes. The largest proportion of discrimination lies in the different locomotor functions: apes on the one hand and the humans and fossils on the other. While the fossils have the closest affinity to humans, they have a unique biomechanical pattern suggesting a more facultative form of bipedalism. The implications of this are, while morphometric analyses do not necessarily directly capture the described primitive and derived traits, the associated functional pattern is held within the broader morphology of the bone.     

Cranial morphometry of early hominids: facial region

We report here on early hominid facial diversity, as part of a more extensive morphometric survey of cranial variability in Pliocene and early Pleistocene Hominidae. Univariate and multivariate techniques are used to summarise variation in facial proportions in South and East African hominids, and later Quaternary groups are included as comparators in order to scale the variation displayed. The results indicate that "robust" australopithecines have longer, broader faces than the "gracile" form, but that all australopithecine species show comparable degrees of facial projection. "Robust" crania are characterised by anteriorly situated, deep malar processes that slope forwards and downwards. Smaller hominid specimens, formally or informally assigned to Homo (H. habilis, KNM-ER 1813, etc.), have individual facial dimensions that usually fall within the range of Australopithecus africanus, but which in combination reveal a significantly different morphological pattern; SK 847 shows similarly hominine facial proportions, which differ significantly from those of A. robustus specimens from Swartkrans. KNM-ER 1470 possesses a facial pattern that is basically hominine, but which in some respects mimics that of "robust" australopithecines. Early specimens referred to H. erectus possess facial proportions that contrast markedly with those of other Villafranchian hominids and which suggest differing masticatory forces, possibly reflecting a shift in dietary niche. Overall the results indicate two broad patterns of facial proportions in Hominidae: one is characteristic of Pliocene/basal Pleistocene forms with opposite polarities represented by A. boisei and H. habilis; the other pattern, which typifies hominids from the later Lower Pleistocene onwards, is first found in specimens widely regarded as early representatives of H. erectus, but which differ in which certain respects from the face of later members of that species.     

Quantitative three-dimensional shape analysis of the proximal hallucial metatarsal articular surface in Homo, Pan, Gorilla, and Hylobates

Multidimensional morphometrics is used to compare the proximal articular surface of the first metatarsal between Homo, Pan, Gorilla, Hylobates, and the hominin fossils A.L. 333-54 (A. afarensis), SKX 5017 (P. robustus), and OH 8 (H. habilis). Statistically significant differences in articular surface morphology exist between H. sapiens and the apes, and between ape groups. Ape groups are characterized by greater surface depth, an obliquely curved articular surface through the dorso-lateral and medio-plantar regions, and a wider medio-lateral surface relative to the dorso-plantar height. The OH 8 articular surface is indistinguishable from H. sapiens, while A.L. 333-54 and SKX 5017 more closely resemble the apes. P. robustus and A. afarensis exhibit ape-like oblique curvature of the articular surface.     

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.     

Brief Communication: Shape analysis of the MT 1 proximal articular surface in fossil hominins and shod and unshod Homo

As a follow-up study to Proctor et al. (Am J Phys Anthropol 135 (2008) 216-224), this study quantifies the first metatarsal proximal articular surface using three-dimensional morphometrics to test for differences in articular surface shape between habitually shod and habitually unshod humans. In addition, differences in shape between Homo, Pan, Gorilla, and Hylobates are compared to the fossil hominin specimens A. L. 333-54, Stw 562, Stw 573 ("Little Foot"), OH 8, SKX 5017, and SK 1813. No difference in surface shape was found between habitually shod and habitually unshod humans. There is a clear quantitative division in articular surface shape between humans and apes that is more pronounced than a previous study by Proctor et al. (Am J Phys Anthropol 135 (2008) 216-224), due to additional landmarks present in this study. The specimen OH 8 is indistinguishable from modern Homo. The fossils A. L. 333-54, Stw 562, and Stw 573 are intermediate in shape between humans and apes. The specimens SKX 5017 and SK 1813 have a more apelike articular surface. When combined with other characteristics, this trait suggests that Paranthropus used a degree of abduction during locomotion that was much less than that in extant apes, but greater than that in Australopithecus, allowing for some small degree of grasping ability.     

Shape variation of the human pollical distal phalanx and metacarpal

Human distal pollical phalanx form has been associated with tool manufacture, and the broad tuft of this bone in Neanderthals has been suggested to be a climatic adaptation and/or an aid to a tremendously powerful grip. A wide first metacarpal head has also been proposed to be useful in distinguishing tool-dependent hominids from those less reliant on tools. In order to contribute to an evaluation of these hypotheses variation in first metacarpal and distal phalanx shape is explored among samples of modern humans and compared to that of fossil hominids. Modern humans are from the Terry Collection, Larsen Bay, a Chinese-Alaskan cemetery, Egypt, and Sully and Mobridge. Hominid fossils include AL 333w-39, SKX 5016, SK 84, Stw 294, OH 7, several Neanderthals, Skhūl 4 and 5, and Predmostí 3. Analysis involves length-width ratios, regressions of distal phalanx tuft width on base width and of metacarpal head width on length, and pattern profiles based on Z-scores with reference to the Larsen Bay sample. Larsen Bay individuals are robust, while Terry "blacks," Egyptians, and Chinese-Alaskan males tend to be gracile. Fossil hominids are most distinctive for distal phalanx radioulnar tuft and mid-shaft widths relative to length. Security of grip is one plausible explanation. While most modern samples are positively allometric for tuft width relative to base width, the Larsen Bay and fossil hominid samples are not; thus caution is advised in accepting a base-tuft width comparison as a tool-dependence marker. Separation from modern humans is not easily achieved with metacarpal measures, but the Hadar metacarpal has distinctively narrow radioulnar head width ratios. While first metacarpal head expansion among hominids may plausibly be related to tool manufacture, other activities that place stress on the metacarpophalangeal joint should also be considered.     

Inner structural organization of the distal humerus in Paranthropus and Homo

The taxonomic attribution of isolated hominin distal humeri has been a matter of uncertainty and disagreement notwithstanding their relative abundance in the fossil record. Four taxonomically-based morphotypes, respectively representing P. boisei, P. robustus, non-erectus early Homo and H. erectus, have been identified based on the cross-sectional outer shape variation of an assemblage of Plio-Pleistocene eastern and southern African specimens (Lague, 2015). However, the existence of possible differences between Paranthropus and Homo in the inner structural organisation at this skeletal site remains unexplored. We used noninvasive imaging techniques to tentatively characterize the endostructural organization of five early Pleistocene distal humeri from South Africa (TM 1517g, SK 24600, SKX 10924, SKX 34805) and Ethiopia (Gombore IB), which have been variably attributed to Paranthropus or Homo. While the investigated specimens reveal diverse degrees of inner preservation related to their taphonomic and diagenetic history, in all but SK 24600 from Swartkrans we could comparatively assess some geometric properties at the most distal cross-sectional level (%CA, I_x/I_y, I_max/I_min) and quantify cortical bone thickness topographic variation across the preserved shaft portions by means of a 2-3D Relative Cortical Thickness index. Whenever possible, we also provided details about the site-specific organization of the cancellous network and measured the same parameters in a comparative sample of twelve adult extant humans. For most features, our results indicate two main patterns: the first includes the specimens TM 1517g, SKX 10924 and SKX 34805, while the second endostructural morphotype sets apart the robust Homo aff. erectus Gombore IB specimen from Melka Kunture, which more closely resembles the condition displayed by our comparative human sample. Notably, marked differences in the amount and pattern of proximodistal cortical bone distribution have been detected between Gombore IB and SKX 34805 from Swartkrans. Given its discordant outer and inner signatures, we conclude that the taxonomic status of SKX 34805 deserves further investigations.     

Effects of size and locomotor adaptations on the hominid pelvis: evaluation of australopithecine bipedality with a new multivariate method

Three pelves and eight innominate bones belonging to the fossil species, Australopithecus africanus, Australopithecus robustus, Homo erectus, and Homo sapiens, have been studied biometrically and compared with those of recent humans and apes. A new method of logarithmic factorial analysis suppresses both the size effects and the size reference on pelvic proportions. In combination with principal component analysis it allows specializations to be dissociated from allometrical variations. Some morphological differences on the hominid pelvis prove to be mainly allometric. However, the pelvic morphology of australopithecines is clearly differentiated from that of the genus Homo (including H. erectus, OH 28, KNMER 3227). A. africanus (Sts 14, MLD 7, AL 288) is nearer the humans than is A. robustus (SK 50, SK 3155), which appears to be more specialized in the australopithecine lineage. The pelvic morphology of A. africanus, as integrated with the articular pelvic-femoral link, appears to be biometrically equivalent to that of humans.     

Affinities of the Swartkrans 847 hominid cranium

Further evidence of the presence of a second hominid species at the Swartkrans locality was obtained in 1969 when the SK.847 specimen was discovered by us to represent the same individual as the SK.80 maxilla. The SK.847 specimen had previously been regarded as robust australopithecine, whereas the latter was first attributed to Telanthropus capensis and subsequently to a species of the genus Homo. Recent criticism of our interpretation of these remains has not evaluated and analyzed critically the primary fossil evidence. Instead it relies on a strict adherence to an as yet unsubstantiated hypothesis that posits only a single hominid species at any point in space and time in the Cenozoic history of Hominidae.     

A cranial base of Australopithecus robustus from the hanging remnant of Swartkrans, South Africa

SKW 18, a partial hominin cranium recovered from the site of Swartkrans, South Africa, in 1968 is described. It is derived from ex situ breccia of the Hanging Remnant of Member 1, dated to approximately 1.5-1.8 Mya. Although partially encased in breccia, it was refit to the facial fragment SK 52 (Clarke 1977 The Cranium of the Swartkrans Hominid SK 847 and Its Relevance to Human Origins, Ph.D. dissertation, University of the Witwatersrand, Johannesburg), producing the composite cranium SKW 18/SK 52. Subsequent preparation revealed the most complete cranial base attributable to the species Australopithecus robustus. SKW 18 suffered weathering and slight postdepositional distortion, but retains considerable anatomical detail. The composite cranium most likely represents a large, subadult male, based on the incomplete fusion of the spheno-occipital synchondrosis; unerupted third molar; pronounced development of muscular insertions; and large teeth. Cranial base measures of SKW 18 expand the range of values previously recorded for A. robustus. SKW 18 provides information on anatomical features not previously visible in this taxon, and expands our knowledge of morphological variability recognizable in the cranial base. Morphological heterogeneity in the development of the prevertebral and nuchal muscular insertions is likely the result of sexual dimorphism in A. robustus, while differences in cranial base angles and the development of the occipital/marginal sinus drainage system cannot be attributed to size dimorphism.     

Variation in enamel development of South African fossil hominids

Dental tissues provide important insights into aspects of hominid palaeobiology that are otherwise difficult to obtain from studies of the bony skeleton. Tooth enamel is formed by ameloblasts, which demonstrate daily secretory rhythms developing tissue-specific structures known as cross striations, and longer period markings called striae of Retzius. These enamel features were studied in the molars of two well known South African hominid species, Australopithecus africanus and Paranthropus robustus. Using newly developed portable confocal microscopy, we have obtained cross striation periodicities (number of cross striations between adjacent striae) for the largest sample of hominid teeth reported to date. These data indicate a mean periodicity of seven days in these small-bodied hominids. Important differences were observed in the inferred mechanisms of enamel development between these taxa. Ameloblasts maintain high rates of differentiation throughout cervical enamel development in P. robustus but not in A. africanus. In our sample, there were fewer lateral striae of Retzius in P. robustus than in A. africanus. In a molar of P. robustus, lateral enamel formed in a much shorter time than cuspal enamel, and the opposite was observed in two molars of A. africanus. In spite of the greater occlusal area and enamel thickness of the molars of both fossil species compared with modern humans, the total crown formation time of these three fossil molars was shorter than the corresponding tooth type in modern humans. Our results provide support for previous conclusions that molar crown formation time was short in Plio-Pleistocene hominids, and strongly suggest the presence of different mechanisms of amelogenesis, and thus tooth development, in these taxa.     

The femur in early human evolution.

Uni- and multivariate analyses of 5 fossil and 215 extant hominoid femora show that two morphological patterns of hominid femora existed about two million years ago. Femora classified as Homo sp. indet. (KNMER 1472 and 1481) are more like Homo sapiens although not identical.Those classified as Australopithecus robustus (SK 82 and 97) and A. boisei (KNM-ER 1503) are similar to one another but uniquely different from any living hominoid. The strong mophological constrasts imply biomechanical and possible locomotor differences, although these are as yet unknown.     

New hominin first metatarsal (SK 1813) from Swartkrans

A recently recognized hominin hallucal metatarsal, SK 1813, from Swartkrans bears a suite of primitive and derived traits. Comparisons with extant apes, modern humans, SKX 5017, and Stw 562 reveals similar morphology in all three fossils and that these early hominins, while bipedal, possessed a unique toe-off mechanism. The implications of this are that both primitive and derived traits must be used to establish the total biomechanical pattern.     

Description d’un bassin fragmentaire de Paranthropus robustus du site Plio-Pléistocène de Drimolen (Afrique du Sud)

The Plio-Pleistocene site of Drimolen (Gauteng Province, South Africa) has yielded a fragmentary adult pelvis, DNH 43, composed of a robust, right innominate bone (DNH 43B) associated with the sacrum and the posterior arch of the last lumbar vertebra (DNH 43 A). Comparisons with other Plio-Pleistocene hominids (AL 288.1, Sts 14, Sts 65, Stw 431, TM 1605, SK 50, SK 3155b) pelves have been made which indicate that this specimen belongs to Paranthropus robustus. The ilium of the Drimolen hominid is narrowed just above the acetabulum. The small auricular surface is set far away from the acetabulum. The sacrum is curved, the upper lateral angles are clearly expressed. Some anatomical features reveal a lumbar lordosis in DNH 43. This lumbar lordosis is specific of australopithecines because different from extant human.     

Molecular phylogeography of the Amazonian Chagas disease vectors Rhodnius prolixus and R. robustus

The phylogeographical structure of the closely related species Rhodnius prolixus and R. robustus is presented based on a 663-base pair (bp) fragment of the mitochondrial cytochrome b gene. Twenty haplotypes were recovered from 84 samples examined, representing 26 populations from seven Latin American countries. The resulting phylogenetic tree is composed of five major reciprocally monophyletic clades, one representing R. prolixus and four representing R. robustus. While R. prolixus is a very homogeneous assemblage, R. robustus has deeper clades and is paraphyletic, with the clade comprising R. robustus from Venezuela (Orinoco region) more closely related to the R. prolixus clade than to the other R. robustus populations from the Amazon region. The R. robustus paraphyly was supported further by the analysis of a nuclear gene (D2 region of the 28S RNA) for a subset of specimens. The data support the view that R. robustus represents a species complex. Levels of sequence divergence between clades within each region are compatible with a Pleistocene origin. Nucleotide diversity (pi) for all R. prolixus populations was extremely low (0.0008), suggesting that this species went through a recent bottleneck, and was subsequently dispersed by man.