Hallucial convergence in early hominids

There is a richly documented fossil record of the evolutionary transition from ape-sized brains that are less that one-third the size of modern humans through a series of intermediate-sized brains up to the modern range. The first report on the discovery of the foot of the Stw 573 skeleton emphasized the apparent transitional nature of its great toe [Clarke, R.J., Tobias, P.V., 1995. Sterkfontein Member 2 foot bones of the oldest South African hominid. Science 269, pp. 521-524]. The hallux appeared to be intermediate in its divergence between human-like adduction and ape-like abduction. A major part of this evidence is the medial encroachment of the metatarsal I facet on the medial cuneiform. This study quantifies the variability of this feature in extant hominoids and fossil hominids. The results are consistent with the view that all currently known hominids were specialized for bipedality and lacked the ape-like ability to oppose the great toe.     

A complete second metatarsal (StW 89) from Sterkfontein Member 4, South Africa

The functional anatomy of the hominin foot has played a crucial role in studies of locomotor evolution in human ancestors and extinct relatives. However, foot fossils are rare, often isolated, and fragmentary. Here, we describe a complete hominin second metatarsal (StW 89) from the 2.0-2.6 million year old deposits of Member 4, Sterkfontein Cave, South Africa. Like many other fossil foot bones, it displays a mosaic of derived human-like features and primitive ape-like features. StW 89 possesses a domed metatarsal head with a prominent sulcus, indicating dorsiflexion at the metatarsophalangeal joint during bipedal walking. However, while the range of motion at the metatarsophalangeal joint is human-like in dorsiflexion, it is ape-like in plantarflexion. Furthermore, StW 89 possesses internal torsion of the head, an anatomy decidedly unlike that found in humans today. Unlike other hominin second metatarsals, StW 89 has a dorsoplantarly gracile base, perhaps suggesting more midfoot laxity. In these latter two anatomies, the StW 89 second metatarsal is quite similar to the recently described second metatarsal of the partial foot from Burtele, Ethiopia. We interpret this combination of anatomies as evidence for a low medial longitudinal arch in a foot engaged in both bipedal locomotion, but also some degree of pedal, and perhaps even hallucal, grasping. Additional fossil evidence will be required to determine if differences between this bone and other second metatarsals from Sterkfontein reflect normal variation in an evolving lineage, or taxonomic diversity.     

The morphology of the gluteus maximus during human evolution: Prerequisite or consequence of the upright bipedal posture?

The human gluteus maximus differs from that of the other hominoids because of its size and bony attachments. These differences raise questions concerning their sequence of appearance in human evolution. Given that humans practice a unique locomotor style, one wonders if the human gluteus maximus morphology is a prerequisite or a consequence of upright bipedal locomotion. This question is addressed using a computer model that evaluates muscle leverage in a variety of locomotor postures. In this model, the human-like, or ape-like, muscular pattern is imposed upon a representative hindlimb of each of the five extant hominoids. Shapes of the skeletal elements (i.e. ilium and ischium lengths) are adjusted in the computer to simulate an evolutionary progression from an ape to a human skeletal morphology. Changes in the leverage of different parts of the gluteus maximus (measured as moment arms) are monitored during this transition. The results show how the mechanical leverages of the gluteus maximus would have changed in a variety of hypothetical evolutionary sequences that describe an ape to human transition. Although the hominoid models exhibit minor differences in these simulations, they all show that the postural and locomotor functions of the gluteus maximus would become more difficult if musculoskeletal morphology changed to the human-like pattern before erect bipedal posture was adopted. Conversely, small adjustments in the ape-like musculoskeletal condition support an erect bipedal posture. These results suggest that a human like posture would have preceded the appearance of the human-like musculoskeletal morphology. Human gluteal morphology, therefore, is a consequence and not a prerequisite of the upright bipedal posture.     

Morphological affinities of the Australopithecus afarensis hand on the basis of manual proportions and relative thumb length

The hands of apes and humans differ considerably with regard to proportions between several bones. Of critical significance is the long thumb relative to other fingers, which is the basis for human-like pad-to-pad precision grip capability, and has been considered by some as evidence of tool-making. The nature and timing of the evolutionary transition from ape-like to human-like manual proportions, however, have remained unclear as a result of the lack of appropriate fossil material. In this article, the manual proportions of Australopithecus afarensis from locality AL 333/333w (Hadar, Ethiopia) are investigated by means of bivariate and multivariate morphometric analyses, in order to test the hypothesis that human-like proportions, including an enhanced thumb/hand relationship, originally evolved as an adaptation to stone tool-making. Although some evidence for human-like manual proportions had been previously proposed for this taxon, conclusive evidence was lacking. Our results indicate that A. afarensis possessed overall manual proportions, including an increased thumb/hand relationship that, contrary to previous reports, is fully human and would have permitted pad-to-pad human-like precision grip capability. We show that these human-like proportions in A. afarensis mainly result from hand shortening, as in modern humans, and that these conclusions are robust enough as to be non-dependent on whether the bones belong to a single individual or not. Since A. afarensis predates the appearance of stone tools in the archeological record, the above-mentioned conclusions permit a confident refutation of the null hypothesis that human-like manual proportions are an adaptation to stone tool-making, and thus alternative explanations must be therefore sought. One hypothesis would consider manipulative behaviors (including tool-use and/or non-lithic tool-making) in early hominines exceeding those reported among extant non-human primates. Alternatively, on the basis of the many adaptations to committed bipedalism in A. afarensis, we propose the hypothesis that once arboreal behaviors became adaptively insignificant and forelimb-dominated locomotor selection pressures were relaxed with the adoption of terrestrial bipedalism, human-like manual proportions could have merely evolved as a result of the complex manipulation selection pressures already present in extant non-human primates.Both hypotheses are not mutually exclusive, and even other factors such as pleiotropy cannot be currently discarded.     

A hominoid distal tibia from the Miocene of Pakistan

A distal tibia, YGSP 1656, from the early Late Miocene portion of the Chinji Formation in Pakistan is described. The fossil is 11.4 million years old and is one of only six postcranial elements now assigned to Sivapithecus indicus. Aspects of the articular surface are cercopithecoid-like, suggesting some pronograde locomotor activities. However, YGSP 1656 possesses an anteroposteriorly compressed metaphysis and a mediolaterally thick medial malleolus, ape-like features functionally related to orthograde body postures and vertical climbing. YGSP 1656 lacks specializations found in the ankle of terrestrial cercopithecoids and thus Sivapithecus may have been primarily arboreal. Nevertheless, the morphology of this tibia is unique, consistent with other interpretations of Sivapithecus postcranial functional morphology that suggest the locomotion of this ape lacks a modern analog. Based on the limited postcranial remains from S. indicus, we hypothesize that this taxon exhibited substantial body size dimorphism.     

Hemisoleus and reversed hemisoleus flaps

This paper reports an anatomic study of the soleus muscle and clinical applications of the findings derived from the study. Soleus neurovascular anatomy was studied in 86 limbs by dissection and specimen angiography. A consistently present bipenniform muscle morphology was found with medial and lateral subunits that had independent distal neurovascular supplies. This anatomic feature allows surgically splitting the muscle for transfer of one-half the muscle as a flap (hemisoleus muscle flaps). A series of 33 patients using both medial and lateral hemisoleus flaps in both proximally and distally based transfer is analyzed and illustrative examples are presented. The primary value of this technique is the ability to retain one-half the innervated soleus muscle in situ to preserve foot plantar flexion power in ambulatory patients. In addition, hemisoleus flaps have an extended arc of rotation as compared with that of conventional soleus muscle flaps.     

The geological context of the Kanapoi fossil hominids

Recent study of the geological succession at Kanapoi reveals that there are at least three series of sediments younger than the early Pliocene Kanapoi sediments which repose unconformably on them. Both sets of terrace and placage deposits contain an admixture of reworked Pliocene fossils and younger fossils preserved at the time of deposition of the younger sediments. This discovery throws doubt on the homogeneous nature of the Kanapoi fossil hominid sample, and suggests instead thatAustralopithecus anamensis may consist of a chimera of an early Pliocene hominid with generally ape-like dentognathic and postcranial anatomy and considerably youngerHomo specimens with more human-like post-cranial bones.     

Adaptation to bipedal gait and fifth metatarsal structural properties in Australopithecus,Paranthropus, and Homo

Humans, unlike African apes, have relatively robust fifth metatarsals (Mt5) presumably reflecting substantial weight-bearing and stability function in the lateral column of the former. When this morphological difference emerged during hominin evolution is debated. Here we investigate internal diaphyseal structure of Mt5s attributed to Australopithecus (from Sterkfontein), Paranthropus (from Swartkrans), and Homo (from Olduvai, Dmanisi, and Dinaledi) placed in the context of human and African ape Mt5 internal diaphyseal structure. ‘Whole-shaft’ properties were evaluated from 17 cross sections sampling 25% to 75% diaphyseal length using computed tomography. To assess structural patterns, scaled cortical bone thicknesses (sCBT) and scaled second moments of area (sSMA) were visualized and evaluated through penalized discriminant analyses. While the majority of fossil hominin Mt5s exhibited ape-like sCBT, their sSMA were comparatively more human-like. Human-like functional loading of the lateral column existed in at least some fossil hominins, although perhaps surprisingly not in hominins from Dmanisi or Dinaledi.     

Early Origin for Human-Like Precision Grasping: A Comparative Study of Pollical Distal Phalanges in Fossil Hominins

Background

The morphology of human pollical distal phalanges (PDP) closely reflects the adaptation of human hands for refined precision grip with pad-to-pad contact. The presence of these precision grip-related traits in the PDP of fossil hominins has been related to human-like hand proportions (i.e. short hands with a long thumb) enabling the thumb and finger pads to contact. Although this has been traditionally linked to the appearance of stone tool-making, the alternative hypothesis of an earlier origin—related to the freeing of the hands thanks to the advent of terrestrial bipedalism—is also possible given the human-like intrinsic hand proportion found in australopiths.

Methodology/Principal Findings

We perform morphofunctional and morphometric (bivariate and multivariate) analyses of most available hominin pollical distal phalanges, including Orrorin, Australopithecus, Paranthropous and fossil Homo, in order to investigate their morphological affinities. Our results indicate that the thumb morphology of the early biped Orrorin is more human-like than that of australopiths, in spite of its ancient chronology (ca. 6 Ma). Moreover, Orrorin already displays typical human-like features related to precision grasping.

Conclusions

These results reinforce previous hypotheses relating the origin of refined manipulation of natural objects–not stone tool-making–with the relaxation of locomotor selection pressures on the forelimbs. This suggests that human hand length proportions are largely plesiomorphic, in the sense that they more closely resemble the relatively short-handed Miocene apes than the elongated hand pattern of extant hominoids. With the advent of terrestrial bipedalism, these hand proportions may have been co-opted by early hominins for enhanced manipulative capabilities that, in turn, would have been later co-opted for stone tool-making in the genus Homo, more encephalized than the previous australopiths. This hypothesis remains may be further tested by the finding of more complete hands of unequivocally biped early hominins.     

Further observations on a method for estimating hominoid dental developmental patterns

Several recent studies have concluded that early hominines resembled apes in patterns of dental ontogeny and have inferred from this conclusion that they were ape-like in other aspects of growth and development as well. Prior to their employment on fossil junveniles, the comparative methods used in these studies were not first tested for their predicitive accuracy in distinguishing modern humans from apes on the basis of proposed patterns of dental ontogeny. We find that 92% of a smaple of 48 modern children are classified as ape-like or nonhuman by the criteria employed in one of these studies and overlap entirely with fossil juvenile dental patterns. The use of these methods to characterize early hominines as “ape-like” or distinctly divergent from humans is thus shown to be unwarranted. © 1993 Wiley-Liss, Inc.     

A comparison of the nariokotome Homo erectus with juveniles from a modern human population.

The Nariokotome Homo erectus has an apparent disjunction of inferred age as judged by dental maturity, by epiphyseal closure and by stature, when compared to modern human norms. On this basis, it has been suggested that this fossil hominin differed in its pattern of growth and development from modern humans. In particular, the characteristic human adolescent growth spurt may not yet have been present, and in this sense H. erectus growth would be more ape-like than human-like. This study tests this conclusion by examining the variation in age as inferred from the maturity indicators in a modern human skeletal population of known age. The results show that all of the maturity indicators used in this analysis underage the test skeletons. Furthermore, there is also no consistency between the indicators; they do not agree in their inferred chronological ages. The disjunction between the maturity indicators in the test skeletons is similar in pattern to the disjunction observed in the Nariokotome Homo erectus. This is particularly true of the relationship between dental age and the other two indicators. These results suggest that the pattern observed in Nariokotome is within the normal range of variation found in modern humans. It does not necessarily indicate a different pattern of growth and development.     

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.     

Shared human-chimpanzee pattern of perinatal femoral shaft morphology and its implications for the evolution of hominin locomotor adaptations

Background

Acquisition of bipedality is a hallmark of human evolution. How bipedality evolved from great ape-like locomotor behaviors, however, is still highly debated. This is mainly because it is difficult to infer locomotor function, and even more so locomotor kinematics, from fossil hominin long bones. Structure-function relationships are complex, as long bone morphology reflects phyletic history, developmental programs, and loading history during an individual’s lifetime. Here we discriminate between these factors by investigating the morphology of long bones in fetal and neonate great apes and humans, before the onset of locomotion.

Methodology/Principal Findings

Comparative morphometric analysis of the femoral diaphysis indicates that its morphology reflects phyletic relationships between hominoid taxa to a greater extent than taxon-specific locomotor adaptations. Diaphyseal morphology in humans and chimpanzees exhibits several shared-derived features, despite substantial differences in locomotor adaptations. Orangutan and gorilla morphologies are largely similar, and likely represent the primitive hominoid state.

Conclusions/Significance

These findings are compatible with two possible evolutionary scenarios. Diaphyseal morphology may reflect retained adaptive traits of ancestral taxa, hence human-chimpanzee shared-derived features may be indicative of the locomotor behavior of our last common ancestor. Alternatively, diaphyseal morphology might reflect evolution by genetic drift (neutral evolution) rather than selection, and might thus be more informative about phyletic relationships between taxa than about locomotor adaptations. Both scenarios are consistent with the hypothesis that knuckle-walking in chimpanzees and gorillas resulted from convergent evolution, and that the evolution of human bipedality is unrelated to extant great ape locomotor specializations.     

A three-dimensional anatomical model of the human patello-femoral joint,for the determination of patello-femoral motions and contact characteristics

The object of this study is to develop a three-dimensional mathematical model of the patello-femoral joint, which is modelled as two rigid bodies representing a moving patella and a fixed femur. Two-point contact was assumed between the femur and patella at the medial and lateral sides and in the analysis, the femoral and patellar articular surfaces were mathematically represented using Coons' bicubic surface patches. Model equations include six equilibrium equations and eleven constraints: six contact conditions, four geometric compatibility conditions, and the condition of a rigid patellar ligament; the model required the solution of a system of 17 nonlinear equations in 17 unknowns, its response describing the six-degress-of-freedom patellar motions and the forces acting on the patella. Patellar motions are described by six motion parameters representing the translations and rotations of the patella with respect to the femur. The forces acting on the patella include the medial and lateral component of patello-femoral contact and the patellar ligament force, all of which were represented as ratios to the quadriceps tendon force. The model response also includes the locations of the medial and lateral contact points on the femur and the patella. A graphical display of its response was produced in order to visualize better the motion of the components of the extensor mechanism.Model calculations show good agreement with experimental results available from the literature. The patella was found to move distally and posteriorly on the femoral condyles as the knee was flexed from full extension. Results indicate that the relative orientation of the patellar ligament with respect to the patella remains unchanged during this motion. The model also predicts a patellar flexion which always lagged knee flexion.Our calculations show that as the angle of knee flexion increased, the lateral contact point moved distally on the femur without moving significantly either medially or laterally. The medial contact point also moved distally on the femur but moved medially from full extension to about 40° of knee flexion, then laterally as the knee flexion angle increased. The lateral contact point on the patella did not change significantly in the medial and lateral direction as the knee was flexed; however, this point moved proximally toward the basis of the patella with knee flexion. The medial contact point also moved proximally on the patella with knee flexion, and in a similar manner the medial contact point on the patella moved distally with flexion from full extension to about 40° of flexion. However, as the angle of flexion increased, the medial contact point did not move significantly in the medial-lateral direction.Model calculations also show that during the simulated knee extension exercise, the ratio of the force in the patellar ligament to the force in the quadriceps tendon remains almost unchanged for the first 30° of knee flexion, then decreases as the angle of knee flexion increases. Furthermore, model results show that the lateral component of the patello-femoral contact force is always greater than the medial component, both components increasing with knee flexion.     

A morphometric analysis of maxillary molar crowns of Middle-Late Pleistocene hominins

This study explores the significance of shape differences in the maxillary first molar crowns of Neandertals and anatomically modern humans. It uses morphometric analysis to quantify these differences and to investigate how the orientation of major cusps, relative cusp base areas and occlusal polygon area influence crown shape. The aims of this study were to 1) quantify these data to test whether the tooth shapes of Neandertals and anatomically modern humans differ significantly and 2) to explore if either of the shapes is derived relative to earlier fossil hominins. Data were collected from digital occlusal photographs using image-processing software. Cusp angles, relative cusp base areas and occlusal polygon areas were measured on Neandertals (n=15), contemporary modern humans (n=62), Upper Paleolithic humans (n=6), early anatomically modern humans (n=3) and Homo erectus (n=3). Univariate and multivariate statistical tests were used to evaluate the differences between contemporary modern humans and Neandertals, while the much sparser data sets from the other fossil samples were included primarily for comparison. Statistically significant differences reflecting overall crown shape and internal placement of the crown apices were found. Neandertals are distinguished from contemporary humans by possessing maxillary first molars that 1) are markedly skewed; 2) possess a narrower distal segment of the occlusal polygon compared to the mesial segment; 3) possess a significantly smaller metacone and a significantly larger hypocone; and 4) possess a significantly smaller relative occlusal polygon area reflecting internally placed cusps. Differences in relative cusp base areas of the hypocone and metacone may contribute to the shape differences observed in Neandertals. However, early anatomically modern humans possessing a pattern of relative cusp base areas similar to Neandertals lack their unusual shape. That the morphology observed in non-Neandertal fossil hominins is more anatomically modern human-like than Neandertal-like, suggests that this distinctive morphology may be derived in Neandertals.     

Technical Note: Virtual reconstruction of KNM‐ER 1813 Homo habilis cranium

A very limiting factor for paleoanthropological studies is the poor state of preservation of the human fossil record, where fragmentation and deformation are considered normal. Although anatomical information can still be gathered from a distorted fossil, such specimens must typically be excluded from advanced morphological and morphometric analyses, thus reducing the fossil sample size and, ultimately, our knowledge of human evolution. In this contribution we provide the first digital reconstruction of the KNM‐ER 1813 Homo habilis cranium. Based on state of‐the‐art three‐dimensional digital modeling and geometric morphometric (GM) methods, the facial portion was aligned to the neurocranium, the overall distortion was removed, and the missing regions were restored. The reconstructed KNM‐ER 1813 allows for an adjustment of the anthropometric measurements gathered on the original fossil. It is suitable for further quantitative studies, such as GM analyses focused on skull morphology or for finite element analysis to explore the mechanics of early Homo feeding behavior and diet. Am J Phys Anthropol 153:154–160, 2014. © 2013 Wiley Periodicals, Inc.     

A reinvestigation of the fossil viguiera cronquistII (Compositae)

In view of the significance recently ascribed to the uppermost Oligocene-lowermost Miocene fossilViguiera cronquistii, a putative composite head, a reinvestigation of the type material was considered desirable. The type specimen was obtained on loan from the New York Botanical Garden and investigated with all applicable standard paleobotanical techniques. The specimen consists of a laterally compressed globular head terminally attached to a short stalk. The head is composed of from 5–7 ranks of from 12–15 spirally arranged linear-lanceolate bracts with some smaller ovate bracts near the base. The stalk bears bracts that are proximally appressed and free distally. There is no sign of cuticle, pollen, detailed impressions of cells or any structural presevation beyond gross morphology. There is no structural corroboration for the presumption that the head is composed of anything besides bracts. The type specimen is indeed similar in gross morphology to heads ofViguiera. It is equally similar to the inflorescences of angiosperms other than the composites and even to the cones of certain gymnosperms. This fossil cannot be considered unequivocally to be the remains of a composite.     

Knuckle-walking in Sivapithecus? The combined effects of homology and homoplasy with possible implications for pongine dispersals

Sivapithecus is a Miocene great ape from South Asia that is orangutan-like cranially but is distinctive postcranially. Work by others shows that the humerus resembles large terrestrial cercopithecoids proximally and suspensory hominoids distally, but most functional interpretations nevertheless situate Sivapithecus in an arboreal setting. We present a new quantitative analysis of the Sivapithecus capitate and hamate. Though the functional morphology of both bones suggests some degree of arboreality, the overall morphology is most similar to knuckle-walking African apes. Other features of the Sivapithecus humerus and hind limb are also functionally consistent with knuckle-walking, and we suggest that this locomotor behavior is a valid alternative functional interpretation of the postcranial morphology. We speculate that knuckle-walking in Sivapithecus would have evolved independently from African apes, perhaps for similar ecological reasons. The discovery of a possible pongine knuckle-walker challenges the hypotheses that (1) knuckle-walking evolved only once in hominoids and (2) knuckle-walking is too highly specialized to be the positional behavior from which human bipedalism evolved. The possibility of knuckle-walking in Sivapithecus may help to explain not only the curious combination of characters that typify the postcranium but also the unique postcranial morphology of extant Pongo. Furthermore, it may clarify the distribution of fossil pongines across many ecological zones in Eurasia in the Miocene and Pleistocene, as well as, independently, the spread of African apes across a diversity of environments in equatorial Africa.     

Turonian flora from the fossiliferous flints of Châtellerault (western France)

Three new localities yielding fossiliferous flints are reported from the Châtellerault area (Vienne, western France). They include one archaeological site (La Grande Vallée) and two zones with alterite deposits (L’Aunas and Les Bariollières). Broken surfaces of flint nodules show co-occurrence of marine invertebrates such as bryozoans, echinoids (Micraster Agassiz, Orthopsis Cotteau), gastropods (Acteonella d’Orbigny), rudists, and sponges. The association of Acteonella, Micraster and Orthopsis confirms the Turonian age (Upper Cretaceous) of the fossil assemblage. The marine invertebrates co-occur with plant macroremains including fragments of conifer leafy axes such as Brachyphyllum? Brongn., Frenelopsis (Schenk) emend. J. Watson and Geinitzia Endl., as well as fragments of angiosperm leaves. Plant remains are preserved as siliceous permineralizations, showing the gross morphology and all tissues in three dimensions. The fossil assemblage suggests that sediments were deposited proximally along the shoreline in shallow environment influenced by both continental and marine inputs. This coastal area was close to a conifer-dominated forest ecosystem, Geinitzia being probably one of the main components of the flora.