Olecranon orientation as an indicator of elbow joint angle in the stance phase,and estimation of forelimb posture in extinct quadruped animals

Reconstruction of limb posture is a challenging task in assessing functional morphology and biomechanics of extinct tetrapods, mainly because of the wide range of motions possible at each limb joint and because of our poor knowledge of the relationship between posture and musculoskeletal structure, even in the extant taxa. This is especially true for extinct mammals such as the desmostylian taxa Desmostylus and Paleoparadoxia. This study presents a procedure that how the elbow joint angles of extinct quadruped mammals can be inferred from osteological characteristics. A survey of 67 dried skeletons and 113 step cycles of 32 extant genera, representing 25 families and 13 orders, showed that the olecranon of the ulna and the shaft of the humerus were oriented approximately perpendicular to each other during the stance phase. At this angle, the major extensor muscles maximize their torque at the elbow joint. Based on this survey, I suggest that olecranon orientation can be used for inferring the elbow joint angles of quadruped mammals with prominent olecranons, regardless of taxon, body size, and locomotor guild. By estimating the elbow joint angle, it is inferred that Desmostylus would have had more upright forelimbs than Paleoparadoxia, because their elbow joint angles during the stance phase were approximately 165° and 130°, respectively. Difference in elbow joint angles between these two genera suggests possible differences in stance and gait of these two mammals. J. Morphol. 2009. © 2009 Wiley‐Liss, Inc.     

陕西公王岭蓝田直立人内耳迷路的复原及形态特点

1964年在陕西公王岭发现的蓝田人头骨的形态比周口店直立人和印度尼西亚爪哇直立人原始,其厚重的骨壁及较小的脑量,落入了早期人属成员的变异范围。最新测年结果将蓝田人的生存年代从原先普遍接受的距今115万年提早到大约163万年前,接近能人和南方古猿生存年代变异范围的下限,蓝田人是迄今为止我国发现的有确定年代数据的最早的古人类化石。本文采用高分辨率CT技术对蓝田人的颞骨岩部进行了扫描,对骨性内耳迷路进行了3D虚拟复原,通过与和县直立人、欧洲古老型智人、早期人属成员、南方古猿非洲种、粗壮傍人和现代人内耳迷路的21项测量项目的对比和分析,结果显示蓝田人内耳迷路的测量数据与南方古猿非洲种最接近,其次为现代人和欧洲古老型智人,而与早期人属成员和粗壮傍人相差较大。主成分分析结果显示,蓝田人内耳迷路与早期人属成员、欧洲古老型智人、南方古猿非洲种及现代人都有重叠区域,距离最近的是南方古猿非洲种Sts 5,其次为和县直立人和南方古猿非洲种Sts 19,而与粗壮傍人距离较远。本文研究提供了中更新世中国古人类内耳迷路的形态数据,为进一步探讨蓝田人体质特征演化上的意义提供了参考资料。     

Basicranial flexion,relative brain size,and facial kyphosis in Homo sapiens and some fossil hominids

Comparative work among nonhominid primates has demonstrated that the basicranium becomes more flexed with increasing brain size relative to basicranial length and as the -upper and lower face become more ventrally deflected (Ross and Ravosa [1993] Am. J. Phys. Anthropol. 91:305–324). In order to determine whether modern humans and fossil hominids follow these trends, the cranial base angle (measure of basicranial flexion), angle of facial kyphosis, and angle of orbital axis orientation were measured from computed tomography (CT) scans of fossil hominids (Sts 5, MLD 37/38, OH9, Kabwe) and lateral radiographs of 99 extant humans. Brain size relative to basicranial length was calculated from measures of neurocranial volume and basicranial length taken from original skulls, radiographs, CT scans, and the literature. Results of bivariate correlation analyses revealed that among modern humans basicranial flexion and brain size/basicranial length are not significantly correlated, nor are the angles of orbital axis orientation and facial kyphosis. However, basicranial flexion and orbit orientation are significantly positively correlated among the humans sampled, as are basicranial flexion and the angle of facial kyphosis. Relative to the comparative sample from Ross and Ravosa (1993), all hominids have more flexed basicrania than other primates: Archaic Homo sapiens, Homo erectus, and Australopithecus africanus do not differ significantly from Modern Homo sapiens in their degree of basicranial flexion, although they differ widely in their relative brain size. Comparison of the hominid values with those predicted by the nonhominid reduced major-axis equations reveal that, for their brain size/basicranial length, Archaic and Modern Homo sapiens have less flexed basicrania than predicted. H. erectus and A. africanus have the degree of basicranial flexion predicted by the nonhominid reduced major-axis equation. Modern humans have more ventrally deflected orbits than all other primates and, for their degree of basicranial flexion, have more ventrally deflected orbits than predicted by the regression equations for hominoids. All hominoids have more ventrally deflected orbital axes relative to their palate orientation than other primates. It is argued that hominids do not strictly obey the trend for basicranial flexion to increase with increasing relative brain size because of constraints on the amount of flexion that do not allow it to decrease much below 90°. Therefore, if basicranial flexion is a mechanism for accommodating an expanding brain among non-hominid primates, other mechanisms must be at work among hominids. © 1995 Wiley-Liss, Inc.     

The deciduous lower dentition of Ouranopithecus macedoniensis (Primates, Hominoidea) from the late Miocene deposits of Macedonia, Greece

Two mandibular fragments with associated milk teeth assigned to the late Miocene hominoid primate Ouranopithecus macedoniensis are analyzed. The fossils, which belong to a single individual, were found in the Vallesian locality of "Ravin de la Pluie" of the Axios Valley (Macedonia, Greece). The material is described here and compared with extant and extinct hominoids, allowing assessment of the evolutionary trends in the deciduous lower dentition within the Hominoidea. Hylobatids represent the more primitive pattern. Gorilla is slightly more derived than hylobatids, but less derived than Pongo and Pan, the latter being the most derived. With relatively smaller deciduous canines and more molarized deciduous premolars, Ouranopithecus is more derived than both Pan and Gorilla. Among the fossil hominoids, Proconsul, representing the primitive condition, has a very simple dp(3)and a dp(4)that has a trigonid that is taller than the talonid and which lacks a hypoconulid. Griphopithecus is more derived than Proconsul in having a dp(4) with a lower trigonid, a hypoconulid, and a less oblique cristid obliqua. Australopithecus and Paranthropus possess a similar morphology to that of Homo, while Ardipithecus appears to be more primitive than the latter genera. Ouranopithecus has a more derived lower milk dentition than Proconsul and Griphopithecus, but less derived than Australopithecus and Paranthropus. The comparison of the lower milk dentition of Ouranopithecus confirms our previous conclusions suggesting that this fossil hominoid shares derived characters with Australopithecus and Homo.     

Fossil platyrrhine forelimb bones from the early miocene of Argentina

Primate scapula and ulna fragments of uncertain taxonomic affinity (MACN-SC 101) have been recovered from the Pinturas deposits at Arroyo Feo, Santa Cruz, Argentina in association with Santacrucian (Early Miocene) land mammals. Least-squares regression of body weight on surface area and on height of the glenoid fossa of the scapula indicates an estimated mean weight of 3.6 kg for this individual. On the basis of qualitative and several metric features, the fossil scapula and ulna most closely resemble living platyrrhine monkeys. In estimated body weight and relative height of the coronoid process, the fossil is similar to arboreal quadrupeds, such as Cebus apella and Chiropotes. However, spinoglenoid, axilloglenoid, and axillospinal angles, length of lever arm, and length and breadth of the sigmoid notch imply behavioral similarity with larger species that also use their forelimbs extensively in climbing, such as Alouatta and Lagothrix. MACN-SC 101 may represent the incipient divergence of a generalized platyrrhine arboreal quadruped toward a more suspensory form.     

The lorisiform wrist joint and the evolution of "brachiating" adaptations in the hominoidea.

In lorisines (Loris, Nycticebus, Perodicticus, Arctocebus), the tip of the ulna is reduced to the dimensions of a styloid process, a new and more proximal ulnar head is developed, and the pisiform is displaced distally away from its primitive contact with the ulna. In some Nycticebus, intra-articular tissues separate the ulna from the triquetrum. These traits are not seen in other quadrupedal primates, but they are characteristic of extant hominoids. Among hominoids, these features have been interpreted as adaptations to arm-swinging locomotion. Since hominoid-like features of the wrist joint are found in lorisines, but not in New World monkeys that practice arm-swinging locomotion, these features may have been evolved in both lorisines and large hominoids to enhance wrist mobility for cautious arboreal locomotion involving little or no leaping. Most of the other morphological traits characteristic of modern hominoids can be explained as adaptations to cautious quadrupedalism as well as to brachiation, and may have developed for different reasons in different lineages descended from an unspecialized cautious quadruped resembling Alouatta.     

Mediolateral reaction forces and forelimb anatomy in quadrupedal primates: implications for interpreting locomotor behavior in fossil primates

The forelimb joints of terrestrial primate quadrupeds appear better able to resist mediolateral (ML) shear forces than those of arboreal quadrupedal monkeys. These differences in forelimb morphology have been used extensively to infer locomotor behavior in extinct primate quadrupeds. However, the nature of ML substrate reaction forces (SRF) during arboreal and terrestrial quadrupedalism in primates is not known. This study documents ML-SRF magnitude and orientation and forelimb joint angles in six quadrupedal anthropoid species walking across a force platform attached to terrestrial (wooden runway) and arboreal supports (raised horizontal poles). On the ground all subjects applied a lateral force in more than 50% of the steps collected. On horizontal poles, in contrast, all subjects applied a medially directed force to the substrate in more than 75% of the steps collected. In addition, all subjects on arboreal supports combined a lower magnitude peak ML-SRF with a change in the timing of the ML-SRF peak force. As a result, during quadrupedalism on the poles the overall SRF resultant was relatively lower than it was on the runway. Most subjects in this study adduct their humerus while on the poles. The kinetic and kinematic variables combine to minimize the tendency to collapse or translate forelimbs joints in an ML plane in primarily arboreal quadrupedal primates compared to primarily terrestrial quadrupedal ones. These data allow for a more complete understanding of the anatomy of the forelimb in terrestrial vs. arboreal quadrupedal primates. A better understanding of the mechanical basis of morphological differences allows greater confidence in inferences concerning the locomotion of extinct primate quadrupeds.     

Subchondral Bone Apparent Density and Locomotor Behavior in Extant Primates and Subfossil Lemurs <Emphasis Type="Italic">Hadropithecus</Emphasis> and <Emphasis Type="Italic">Pachylemur</Emphasis>

We analyze patterns of subchondral bone apparent density in the distal femur of extant primates to reconstruct differences in knee posture, discriminate among extant species with different locomotor preferences, and investigate the knee postures used by subfossil lemur species Hadropithecus stenognathus and Pachylemur insignis. We obtained computed tomographic scans for 164 femora belonging to 39 primate species. We grouped species by locomotor preference into knuckle-walking, arboreal quadruped, terrestrial quadruped, quadrupedal leaper, suspensory and vertical clinging, and leaping categories. We reconstructed knee posture using an experimentally validated procedure of determining the anterior extent of the region of maximal subchondral bone apparent density on a median slice through the medial femoral condyle. We compared subchondral apparent density magnitudes between subfossil and extant specimens to ensure that fossils did not display substantial mineralization or degradation. Subfossil and extant specimens were found to have similar magnitudes of subchondral apparent density, thereby permitting comparisons of the density patterns. We observed significant differences in the position of maximum subchondral apparent density between leaping and nonleaping extant primates, with leaping primates appearing to use much more flexed knee postures than nonleaping species. The anterior placement of the regions of maximum subchondral bone apparent density in the subfossil specimens of Hadropithecus and Pachylemur suggests that both species differed from leaping primates and included in their broad range of knee postures rather extended postures. For Hadropithecus, this result is consistent with other evidence for terrestrial locomotion. Pachylemur, reconstructed on the basis of other evidence as a committed arboreal quadruped, likely employed extended knee postures in other activities such as hindlimb suspension, in addition to occasional terrestrial locomotion.     

Cavemen Were Better at Depicting Quadruped Walking than Modern Artists: Erroneous Walking Illustrations in the Fine Arts from Prehistory to Today

The experts of animal locomotion well know the characteristics of quadruped walking since the pioneering work of Eadweard Muybridge in the 1880s. Most of the quadrupeds advance their legs in the same lateral sequence when walking, and only the timing of their supporting feet differ more or less. How did this scientific knowledge influence the correctness of quadruped walking depictions in the fine arts? Did the proportion of erroneous quadruped walking illustrations relative to their total number (i.e. error rate) decrease after Muybridge? How correctly have cavemen (upper palaeolithic Homo sapiens) illustrated the walking of their quadruped prey in prehistoric times? The aim of this work is to answer these questions. We have analyzed 1000 prehistoric and modern artistic quadruped walking depictions and determined whether they are correct or not in respect of the limb attitudes presented, assuming that the other aspects of depictions used to determine the animals gait are illustrated correctly. The error rate of modern pre-Muybridgean quadruped walking illustrations was 83.5%, much more than the error rate of 73.3% of mere chance. It decreased to 57.9% after 1887, that is in the post-Muybridgean period. Most surprisingly, the prehistoric quadruped walking depictions had the lowest error rate of 46.2%. All these differences were statistically significant. Thus, cavemen were more keenly aware of the slower motion of their prey animals and illustrated quadruped walking more precisely than later artists.     

Broken fingers: retesting locomotor hypotheses for fossil hominoids using fragmentary proximal phalanges and high-resolution polynomial curve fitting (HR-PCF)

Phalangeal curvature has frequently been used as a proxy indicator of fossil hominoid and hominin positional behavior and locomotor adaptations, both independently and within the context of broader discussions of the postcranium as a whole. This study used high-resolution polynomial curve fitting (HR-PCF) to measure the shaft curvature of fragmentary proximal phalanges that have previously been excluded from analyses of phalangeal curvature owing to design limitations of existing methods. In doing so, the available sample of fossil specimens was increased substantially, making it possible to test prevailing locomotor hypotheses for many taxa with new specimens. The results generated from the HR-PCF analysis of extant primate manual and pedal phalangeal samples suggest that, although capable of identifying suspensory hominoids with some degree of accuracy, phalangeal curvature values reported for extant terrestrial and arboreal quadrupeds overlap considerably. Consequently, it is difficult to reliably predict the locomotor adaptations for fossil taxa with phalangeal curvatures similar to these groups, although the curvature values reported for most taxa were broadly consistent with existing locomotor hypotheses. Only the curvature values reported for Pierolapithecus, which are most similar to those of suspensory hominoids, are inconsistent with previously published locomotor hypotheses. Likewise, although not inconsistent with bipedality, curvature values reported for Australopithecus confirm earlier conclusions that, despite a general reduction in phalangeal length relative to Pan, these taxa have similar and overlapping ranges of phalangeal curvature.     

Articular morphology of the proximal ulna in extant and fossil hominoids and hominins

Extant hominoids share similar elbow joint morphology, which is believed to be an adaptation for elbow stability through a wide range of pronation-supination and flexion-extension postures. Mild variations in elbow joint morphology reported among extant hominoids are often qualitative, where orangutans are described as having keeled joints, and humans and gorillas as having flatter joints. Although these differences in keeling are often linked to variation in upper limb use or loading, they have not been specifically quantified. Many of the muscles important in arboreal locomotion in hominoids (i.e., wrist and finger flexors and extensors) take their origins from the humeral epicondyles. Contractions of these muscles generate transverse forces across the elbow, which are resisted mainly by the keel of the humeroulnar joint. Therefore, species with well-developed forearm musculature, like arboreal hominoids, should have more elbow joint keeling than nonarboreal species. This paper explores the three- and two-dimensional morphology of the trochlear notch of the elbow of extant hominoids and fossil hominins and hominoids for which the locomotor habitus is still debated. As expected, the elbow articulation of habitually arboreal extant apes is more keeled than that of humans. In addition, extant knuckle-walkers are characterized by joints that are distally expanded in order to provide greater articular surface area perpendicular to the large loads incurred during terrestrial locomotion with an extended forearm. Oreopithecus is characterized by a pronounced keel of the trochlear notch and resembles Pongo and Pan. OH 36 has a morphology that is unlike that of extant species or other fossil hominins. All other hominin fossils included in this study have trochlear notches intermediate in form between Homo and Gorilla or Pan, suggesting a muscularity that is less than in African apes but greater than in humans.     

Ontogeny and phylogeny of the pelvis in Gorilla, Pongo, Pan, Australopithecus and Homo

To examine the evolutionary differences between hominoid locomotor systems, a number of observations concerning the growth of the pelvis among the great apes as compared to modern and fossil hominids are reported. We are interested in the size and shape of the coxal bones at different developmental stages across species that may elucidate the relationship between ontogeny and phylogeny (i.e., heterochrony) in the hominoid pelvis. Our hypotheses are: (1) do rates of absolute growth differ?, (2) do rates of relative growth differ?, and (3) does heterochrony explain these differences? Bivariate and multivariate analyses of pelvic dimensions demonstrate both the diversity of species-specific ontogenetic patterns among hominoids, and an unequivocal separation of hominids and the great apes. Heterochrony alone fails to account for the ontogenetic differences between hominids and the great apes. Compared to recent Homo,Australopithecus can be described as 'hyper-human' from the relative size of the ischium, and short but broad ilium. Australopithecus afarensis differs from Australopithecus africanus by its relatively long pubis. In multivariate analyses of ilium shape, the most complete coxal bone attributed to Homo erectus, KNM-ER 3228, falls within the range of juvenile and adult Australopithecus, whereas Broken Hill falls within the range of modern Homo, suggesting that the modern human ilium shape arose rather recently. Among the great apes, patterns of pelvic ontogeny do not exclusively separate the African apes from Pongo.     

The paleobiology of Amphipithecidae, South Asian late Eocene primates

Analysis of the teeth, orbital, and gnathic regions of the skull, and fragmentary postcranial bones provides evidence for reconstructing a behavioral profile of Amphipithecidae: Pondaungia, Amphipithecus, Myanmarpithecus (late middle Eocene, Myanmar) and Siamopithecus (late Eocene, Thailand). At 5-8 kg, Pondaungia, Amphipithecus, and Siamopithecus are perhaps the largest known Eocene primates. The dental and mandibular anatomy suggest that large-bodied amphipithecids were hard-object feeders. The shape of the mandibular corpus and stiffened symphysis suggest an ability to resist large internal loads during chewing and to recruit significant amounts of muscle forces from both the chewing and non-chewing sides of the jaw so as to increase bite force during mastication. The large spatulate upper central incisor of Pondaungia and projecting robust canines of all the larger amphipithecids suggest that incisal food preparation was important. The molars of Siamopithecus, Amphipithecus, and Pondaungia have weak shearing crests. This, and the thick molar enamel found in Pondaungia, suggests a diet of seeds and other hard objects low in fiber. In contrast, Myanmarpithecus was smaller, about 1-2 kg; its cheek teeth suggest a frugivorous diet and do not imply seed eating. Postcranial bones (humerus, ulna, and calcaneus) of a single large amphipithecid individual from Myanmar suggest an arboreal quadrupedal locomotor style like that of howler monkeys or lorises. The humeral head is rounded, proximally oriented, and the tuberosities are low indicating an extremely mobile glenohumeral joint. The great thickness of the midshaft cortical bone of the humerus implies enhanced ability to resist bending and torsion, as seen among slow moving primate quadrupeds. The elbow joint exhibits articular features for enhanced stability in habitually flexed positions, features also commonly found in slow moving arboreal quadrupeds. The short distal load arm of the calcaneus is consistent with, but not exclusive to, slow, arboreal quadrupedalism, and suggests no reliance on habitual leaping.     

中国远古人类的进化

本文从中国人类化石的年代顺序、共同形态特征、渐进变化、形态的异样性、镶嵌性、与其他地区的基因交流和古文化证据等方面论证了中国人类进化以连续性为主,还与世界其他地区之间有渐增的基因交流。本文还附带讨论了近年云南发现的古猿化石和湖北发现的人科头骨化石。     

Functional-adaptive anatomy of the forelimb in the Didelphidae, and the paleobiology of the Paleocene marsupials Mayulestes ferox and Pucadelphys andinus

An attempt to determine the locomotor activities of Mayulestes ferox (Borhyaenoidea) and Pucadelphys andinus (Didelphoidea) from the early Paleocene site of Tiupampa (Bolivia) is presented. The functional anatomy of the forelimbs of these South American marsupials is compared to that of some living didelphids: Caluromys philander, Micoureus demerarae, Marmosa murina, Didelphis marsupialis, Monodelphis brevicaudata and Metachirus nudicaudatus. Deductions from bone morphology to myology and locomotor behavior in the fossils are inferred from the comparisons with living forms. Some features of the postcranial skeleton, indicative of arboreal adaptations, are found in the extinct marsupials: anteriorly projected acromion, hemispherical head of the humerus, extended humeral lateral epicondylar ridge, medially protruding humeral entepicondyle, proximal ulnar posterior convexity, and deep flexor fossa on the medial side of the ulna. But other features are related to a more terrestrial pattern: the well-developed tubercles of the humeral head, the elongated olecranon process of the ulna, and the oval shape of the radial head. Mayulestes had clear arboreal abilities, but, as a predaceous mammal, probably hunted on the ground. Pucadelphys was less specialized, close to the living Monodelphis, a terrestrial insectivorous form with some skeletal features related to arboreal locomotion that are probably plesiomorphic for marsupials.     

Evolutionary reversals of limb proportions in early hominids? Evidence from KNM-ER 3735 (Homo habilis)

Upper-to-lower limb proportions of Homo habilis are often said to be more ape-like than those of its reputed ancestor, Australopithecus afarensis. Such proportions would either imply multiple evolutionary reversals or parallel development of a relatively short upper limb in A. afarensis and later Homo. However, assessments of limb proportions are complicated by the fragmentary nature of the two known H. habilis skeletons, OH 62 and KNM-ER 3735. Initially, KNM-ER 3735 was compared to A.L. 288-1 (A. afarensis) using a single modern human and chimpanzee as reference. Here, based on a larger comparative sample, we find that the relative size of the distal humerus, radial head, and shaft of both KNM-ER 3735 and A.L. 288-1 lie within the range of variation of modern humans, whereas their sacra are small as is the case for all early hominids. In addition, their manual phalanges are similar in having a gracile base but robust midshaft. Contrary to earlier studies, the fossils are not differentiable from each other statistically with respect to all features listed above. On the other hand, they differ in robusticity of the scapular spine and relative length of the radial neck. An exact randomization test suggests only a very low probability of finding a similar degree of difference within a single species of extant hominoids. In contrast to the consensus view, we conclude that A.L. 288-1 had a short, human-like forearm, whereas KNM-ER 3735 possessed a distinctly longer forearm and more powerful shoulder girdle. This interpretation fits with earlier conclusions that suggested human-like humerofemoral proportions but chimpanzee-like brachial proportions for Homo habilis. Thus, the scenario of a unidirectional, progressive change in limb proportions within the hominid lineage is not supported by our work.     

Evolution of mandibular arcades: a statistical study

The alveolar arcades of a large number of fossil mandibles including Australopithecus and hominids fromHomo habilis andHomo erectus up to modern man have been characterized by fourteen cartesian points each representing a tooth. From these points, dimensions and angles have been calculated. These values are correlated to the geological age of the fossils. A linear dependance of dimensions and angles on the logarithm of age has been found. These results are discussed in the framework of a continuous gradual development within genus Homo and contrasted to prehominid data. Using these mean arcades and selected angles thereon the European and the AfroasiaticHomo erectus are compared and contrasted to the Neandertalians.     

Evolutionary transformation of the hominin shoulder

Despite the fact that the shoulder is one of the most extensively studied regions in comparative primate and human anatomy, two recent fossil hominin discoveries have revealed quite unexpected morphology. The first is a humerus of the diminutive fossil hominin from the island of Flores, Homo floresiensis (LB1/50), which displays a very low degree of humeral torsion 1 , 2 (Fig. 1; see Box 1). Modern humans have a high degree of torsion and, since this is commonly viewed as a derived feature shared with hominoids, 3 - 6 one would expect all fossil hominins to display high humeral torsion. The second is the recently discovered Australopithecus afarensis juvenile scapula DIK‐1‐1 from Dikika, Ethiopia, which seems to most closely resemble those of gorillas. 7 This specimen is the first nearly complete scapula known for an early hominin and, given the close phylogenetic relationship between humans and chimpanzees suggested by molecular studies, 8 - 13 one would have expected more similarity to chimpanzees among extant hominoids.     

Radius of Paranthropus robustus from member 1, Swartkrans formation, South Africa

Recently recovered hominid postcrania from Member 1, Swartkrans Formation include the proximal and distal ends of a right radius attributed to a single individual of Paranthropus robustus. These fossils are essentially similar to Australopithecus afarensis, A. africanus, and P. boisei homologues. The head manifests an ape-like circumferentia articularis, and the distal end has prominent medial, dorsal, and lateral tubercles and a well developed brachioradialis crest, features also commonly exhibited by extant great apes. The volar set of the P. robustus radiocarpal joint, like that of Australopithecus homologues, more closely resembles the neutral condition exhibited by Homo than the greater flexion evinced by living apes. Compared with fossil and recent specimens of Homo, the configuration of the P. robustus radial head suggests enhanced stability against medial displacement during pronation and supination; the strong crest for the attachment of brachioradialis may attest to enhanced forearm flexor capability. In addition, this crest and the prominent dorsal tubercles may indicate enhanced hand extensor and, therefore, hand flexor capabilities. The differences in radial morphology between Paranthropus and Homo may relate to significant behavioral differences between these two synchronic taxa.     

New hominid fossils from the Swartkrans formation (1979-1986 excavations): postcranial specimens

New postcranial fossils of Paranthropus robustus and Homo cf. erectus were recovered from Swartkrans from 1979 through 1986. These fossils are from Members 1, 2, and 3. The new fossils are described here along with their morphological affinities. Fossils that are assigned to Paranthropus indicate that the South African "robust" australopithecines engaged in tool behavior and were essentially terrestrial bipeds at around 1.8 Myr BP. The manual dexterity and bipedal locomotion of Paranthropus may have equaled that of Homo habilis in East Africa at approximately the same time.