Morphological study of the anthropoid thoracic cage: scaling of thoracic width and an analysis of rib curvature

While a relatively broad thorax and strongly curved ribs are widely regarded as common features of living hominoids, few studies have quantitatively examined these traits by methods other than calculating the chest index. The present study aims to quantify variations in thoracic cage morphology for living anthropoids. The odd-numbered ribs (first to eleventh) were articulated with the corresponding vertebrae and the cranial and lateral views subsequently photographed. Rib profiles were digitized in both views and line-fitted by a Bézier curve to create a three-dimensional morphological data set. When thoracic cage width was scaled against body mass, Hylobates (and possibly Pongo) plotted above non-hominoid anthropoids at almost all rib levels, while Pan did not differ from non-hominoid anthropoids. The overall pattern of the normalized thoracic width differed between Hylobates and other hominoids. In Hylobates, an upward convex curve was seen between the first and seventh ribs while a more linear pattern was observed in Pan and Pongo. This result quantitatively confirmed that the barrel-shaped thoracic cage in Hylobates can be distinguished from the funnel-shaped form in other hominoids. Conversely, all hominoids shared two distinct features in the upper half-thorax: (1) a pronounced dorsal protrusion of the proximal part of the rib in accordance with ventral displacement of the thoracic spine and (2) a relatively medially projecting sternal end. Although these features are likely to provide some mechanical advantage in orthograde and/or suspensory positional behaviors, they were barely present in the suspensory Ateles. An erratum to this article can be found at     

Vertebral morphology of Nacholapithecus kerioi based on KNM-BG 35250

This paper describes the morphology of the vertebral remains of the KNM-BG 35250 Nacholapithecus kerioi individual from the Middle Miocene of Kenya. Cervical vertebrae are generally large relative to presumed body mass, suggesting a heavy head with large jaws and well-developed neck muscles. The atlas retains the lateral and posterior bridges over the vertebral artery. The axis has a robust dens and a large angle formed by superior articular surfaces. The thoracic vertebral specimens include the diaphragmatic vertebra and one post-diaphragmatic vertebra. The thoracic vertebral bodies are much smaller that those of male Papio cynocephalus, whereas many of the dorsal elements are large and robust, exceeding those of male P. cynocephalus. Lumbar vertebral bodies are small relative to body mass, craniocaudally moderately long, and have a median ventral keel. The transverse process is craniocaudally long and arises from the widest part of the body cranially and the pedicle above the inferior vertebral notch caudally. Anapophyses are present in one of the preserved lumbar vertebrae. The postzygapophyses are thick dorsoventrally. These lumbar features are broadly shared with Proconsul. However, the base of the spinous process is longer and more caudally positioned in N. kerioi compared to Proconsul, and is more similar to the condition in Pongo. They are not dorsally (or moderately caudally) directed as is seen in P. nyanzae, Pan, and most other extant primates. A caudally directed spinous process does not permit a broad range of spinal dorsiflexion. The presumed stiff back in N. kerioi suggests a different locomotor repertoire than in Proconsul. Morotopithecus bishopi, although not possessing the same features, exhibits another morphological suite of characters for lumbar stiffness. Diverse functional adaptations of the lumbar spine were present in African hominoids during the Early to Middle Miocene.     

Metatarsophalangeal joint function and positional behavior in Australopithecus afarensis

Recent discussions of the pedal morphology of Australopithecus afarensis have led to conflicting interpretations of australopithecine locomotor behavior. We report the results of a study using computer aided design (CAD) software that provides a quantitative assessment of the functional morphology of australopithecine metatarsophalangeal joints. The sample includes A. afarensis, Homo sapiens, Pan troglodytes, Gorilla gorilla, and Pongo pygmaeus. Angular measurements of the articular surfaces relative to the long axes of the metatarsals and phalanges were taken to determine whether the articular surfaces are plantarly or dorsally oriented. Humans have the most dorsally oriented articular surfaces of the proximal pedal phalanges. This trait appears to be functionally associated with dorsiflexion during bipedal stride. Pongo has the most plantarly oriented articular surfaces of the proximal pedal phalanges, probably reflecting an emphasis on plantarflexion in arboreal positional behaviors, while the African hominoids are intermediate between Pongo and Homo for this characteristic. A. afarensis falls midway between the African apes and humans. Results from an analysis of metatarsal heads are inconclusive with regard to the functional morphology of A. afarensis. Overall, the results are consistent with other evidence indicating that A. afarensis was a capable climber. © 1994 Wiley-Liss, Inc.     

Rib orientation and implications for orthograde positional behavior in nonhuman anthropoids

Strong caudal obliquity of the lower ribs is one of the assumed characteristics of the thoracic region in hominoids and Ateles. Strong caudal obliquity keeps the scapula of the weight-bearing forelimb on the dorsal surface of the trunk via the serratus anterior muscles during propulsion (Stern et al. 1980). We examined the orientation of odd-numbered ribs in lateral view in remounted thoracic skeletons of fifteen nonhuman anthropoids. Hominoids exhibit pronounced caudal obliquity in the seventh and ninth ribs compared to Old and New World monkeys. The position of the maximum thoracic cage width, which approximates the attachment of the serratus anterior muscle, is more caudally located in Hylobates and Pongo. The overall pattern of rib obliquity is generally similar between New and Old World monkeys, including Ateles. Perhaps not only forelimb suspensory behavior but also various orthograde positional behaviors are related to the strong obliquity of the lower ribs; however, further investigation is necessary.     

First hominoid from the Miocene of Ethiopia and the evolution of the catarrhine elbow

The first known fossil ape from the early-middle Miocene of Fejej, Ethiopia, is described here. The specimen, FJ-18SB-68, is a partial ulna from a locality dated by ⁴⁰Ar/³⁹Ar and paleomagnetic methods to a minimum age of 16.18 MYA. Compared to a variety of extant and fossil ulnae, FJ-18SB-68 is most similar to Turkanapithecus, Proconsul, and Pliopithecus, and appears to have been an arboreal quadruped with substantial forearm rotational mobility. Among the extant ulnae, canonical variates analysis successfully discriminates platyrrhines from catarrhines and within the latter, cercopithecoids from hominoids. Basal catarrhines (e.g., Aegyptopithecus) are platyrrhine-like in their morphology. Two basic trends appear to evolve from this generalized template: one with less mobile and more habitually pronated forearms, as seen in living and fossil cercopithecoids (including Victoriapithecus and Paracolobus), and another with greater forearm rotational mobility in fossil and modern hominoids. Primitive Miocene apes, including Proconsul, Turkanapithecus, and FJ-18SB-68, share with extant hominoids a more laterally positioned and laterally facing radial notch and an incipient trochlear keel. This morphology, along with a large insertion area for m. brachialis, suggests a departure from the more habitually pronated hand posture of monkeys and may indicate greater climbing abilities in these arboreally quadrupedal apes. Later Miocene apes, such as Oreopithecus and Dryopithecus share additional morphological features with hominoids, indicating considerable suspensory and climbing capabilities. Am J Phys Anthropol 105:257–277, 1998. © 1998 Wiley-Liss, Inc.     

Hominoid phalanges from the middle Miocene site of Paşalar, Turkey

Eleven proximal and ten intermediate partial or complete hominoid phalanges have been recovered from the middle Miocene site of Pa?alar in Turkey. Based on species representation at Pa?alar, it is likely that most or all of the phalanges belong to Griphopithecus alpani rather than Kenyapithecus kizili, but both species may be represented. All of the complete or nearly complete phalanges appear to be manual, so comparisons to extant and other fossil primate species were limited to manual phalanges. Comparisons were made to extant hominoid and cercopithecoid primate genera expressing a variety of positional repertoires and varying degrees of arboreality and terrestriality. The comparisons consisted of a series of bivariate indices derived from previous publications on Miocene catarrhine phalangeal morphology. The proximal phalanges have dorsally expanded proximal articular surfaces, which is characteristic of cercopithecoids and most other Miocene hominoids, and indicates that the predominant positional behaviors involved pronograde quadrupedalism. Among the extant primates, many of the proximal and intermediate phalangeal indices clearly distinguish more habitually terrestrial taxa from those that are predominantly arboreal, and especially from taxa that commonly engage in suspensory activities. For nearly every index, the values of the Pa?alar phalanges occupy an intermediate position-most similar to values for Pan and, to a lesser extent, Macaca-indicating a generalized morphology and probably the use of both arboreal and terrestrial substrates. At least some terrestrial activity is also compatible with reconstructions of the Pa?alar habitat. Most proximal and intermediate phalanges of other middle and late Miocene hominoids have similar index values to those of the Pa?alar specimens, revealing broadly similar manual phalangeal morphology among many Miocene hominoids.     

Positional Behavior of Black Spider Monkeys (Ateles paniscus) in French Guiana

Spider monkeys (Ateles) frequently use suspensory locomotion and postures, and their postcranial morphology suggests convergence with extant hominoids in canopy and food utilization. Previous studies of positional behavior in Ateles, have produced variable rates in the use of different positional activities. I investigated the positional behavior of black spider monkeys (Ateles paniscus) in a wet rain forest in French Guiana, and assessed differences in the rates of use of positional modes across studies. I also discuss the significance of suspensory activities in forest utilization. In French Guiana, Ateles confined travel and feeding locomotion on small and medium-sized moderately inclined supports in the main canopy. Tail-arm brachiation and clamber were their main traveling modes, while clamber was the dominant feeding locomotor mode. Small horizontal supports were predominant during their feeding. Suspensory postures accounted for more than half of feeding bouts, with tail-hang and tail-hind limb(s) hang being the dominant postures. Feeding occurred largely in tree crown peripheries with the prehensile tail anchored frequently above the monkey. They usually collected food items below or at the same level as the body. There is no difference among the postures they used to acquire and eat young leaves and fruit. My results agree with reports on the positional behavior of different species of spider monkeys at other sites. Despite the use of different methods, the same species exhibited more or less similar profiles in similar forests. Interspecific differences could be associated with morphological differences. Moreover, intraspecific differences could be attributed to forest structure. The findings suggest that the major part of biological information is independent of methods used in the several studies. Suspensory behavior facilitates the exploitation of the forest canopy by shortening traveling pathways between and within trees, by enabling faster travel for the better exploitation of patchy food sources and by providing access to food in the flexible terminal twigs.     

Morphological correlates of tail length in the catarrhine sacrum

Taillessness is a distinctive synapomorphy of the Hominoidea that has implications for interpretation of the locomotor behaviors and phylogenetic affinities of the clade’s earliest members. However, difficulties persist in confidently identifying taillessness in the catarrhine fossil record, stemming largely from our limited knowledge of the anatomical features with which the tail is associated. Here, we compare the morphology of the sacrum, the sole bony link between the tail and the rest of the body, among extant tailless hominoids and a broad sample of extant cercopithecoids known to vary in tail length (i.e., ‘very short’, ‘short’, and ‘long’) in order to identify morphological correlates of tail length. We examine three features of the sacrum, including the shape of the sacrum’s caudal articular surface (CAS), the sacrocaudal articulation (SCA) angle, and the lateral expansion of the last sacral vertebra’s transverse processes. Compared with all other taxa, ‘long’-tailed cercopithecoids have significantly more circularly-shaped CASs, more acute SCA angles, and more laterally expanded transverse processes of the last sacral vertebra. Tailless hominoids have significantly more elliptically-shaped CASs and less laterally expanded transverse processes than all tailed cercopithecoids, but in the latter parameter, they only differ significantly from ‘long’-tailed cercopithecoids. Cercopithecoids with ‘short’ and ‘very short’ tails are intermediate between tailless hominoids and ‘long’-tailed cercopithecoids with respect to CAS shape and lateral expansion of the transverse processes. SCA angle distinguishes clearly among all three cercopithecoid tail length groups. The results of this study provide evidence for significant differences in sacral morphology among extant catarrhines known to differ in tail length, and have implications for making inferences about tail length and function in extinct catarrhines.     

Scaling of lumbar vertebrae in anthropoids and implications for evolution of the hominoid axial skeleton

We investigated allometric relationships between vertebral centrum cranial surface areas and body weight and skeletal lumbar length in extant platyrrhine and cercopithecid species. Platyrrhines have smaller lumbar vertebral centra regarding the cranial surface area relative to their body weight than extant catarrhines. However, the stress to the spine of quadrupeds is not only influenced by the body weight but also its length, which contributes to the amount of bending moment. Our results indicated that platyrrhines and cercopithecids have similar lumbar vertebral centrum surface areas when they are scaled on the product of the body weight and skeletal lumbar length. Platyrrhines generally tend to have relatively short lumbar columns for a given body weight. As a result of this tendency, their vertebral centra appear relatively small if only body weight is taken into account. The centrum surface area is rather constant relative to the product of the body weight and skeletal lumbar length within platyrrhines or cercopithecids, despite the fact that skeletal lumbar length is in itself rather variable relative to body weight. This result indicates that the vertebral centrum articular area, the lumbar column length and the body weight are strongly correlated with each other and that such relationships are similar between platyrrhines and cercopithecids. These relationships were observed using both the zygapophyseal and rib definitions of the lumbar vertebrae. However, they were more clearly observed when the zygapophyseal definition was adopted. It appeared that lumbar vertebrae of Proconsul nyanzae (KNM−MW 13142) had distinctively smaller surface areas relative to its body weight and lumbar length than for platyrrhines and cercopithecids, differing from extant hominoids, which have comparatively larger lumbar vertebrae. In the case of Morotopithecus, the lumbar vertebral surface area seems to be as large as in extant platyrrhines and cercopithecids if it had a reduced number of lumbar vertebrae. It is uncertain whether its lumbar vertebral surface area was as large as in extant hominoids. Electronic Publication     

Molecular Evolution of Cytochrome c Oxidase Subunit IV: Evidence for Positive Selection in Simian Primates

Cytochrome c oxidase (COX) is a multi-subunit enzyme complex that catalyzes the final step of electron transfer through the respiratory chain on the mitochondrial inner membrane. Up to 13 subunits encoded by both the mitochondrial (subunits I, II, and III) and nuclear genomes occur in eukaryotic organisms ranging from yeast to human. Previously, we observed a high number of amino acid replacements in the human COX IV subunit compared to mouse, rat, and cow orthologues. Here we examined COX IV evolution in the two groups of anthropoid primates, the catarrhines (hominoids, cercopithecoids) and platyrrhines (ceboids), as well as one prosimian primate (lorisiform), by sequencing PCR-amplified portions of functional COX4 genes from genomic DNAs. Phylogenetic analysis of the COX4 sequence data revealed that accelerated nonsynonymous substitution rates were evident in the early evolution of both catarrhines and, to a lesser extent, platyrrhines. These accelerated rates were followed later by decelerated rates, suggesting that positive selection for adaptive amino acid replacement became purifying selection, preserving replacements that had occurred. The evidence for positive selection was especially pronounced along the catarrhine lineage to hominoids in which the nonsynonymous rate was first faster than the synonymous rate, then later much slower. The rates of three types of ``neutral DNA' nucleotide substitutions (synonymous substitutions, pseudogene nucleotide substitutions, and intron nucleotide substitutions) are similar and are consistent with previous observations of a slower rate of such substitutions in the nuclear genomes of hominoids than in the nuclear genomes of other primate and mammalian lineages. Received: 22 May 1996 / Accepted: 24 November 1996     

Brief communication: New primate remains from the Miocene of Namibia,Southern Africa

Miocene primates from southern Africa are extremely rare. For this reason we wish to place on record several interesting new fossil primate specimens recently recovered from the Miocene sites of Berg Aukas and Harasib in the Otavi Mountain region of northern Namibia. The new finds consist of a virtually complete atlas vertebra from Berg Aukas attributable to the hominoid Otavipithecus namibiensis and two teeth and four postcranial fragments from Harasib referrable to Cercopithecoidea. The atlas vertebra exhibits anatomical characteristics intermediate between those of modern cercopithecoids and hominoids which may be indicative of a transition from pronograde to orthograde postures. The cercopithecoid remains show that the earliest Old World monkeys known from southern Africa were small, approximately the size of vervet monkeys. These new specimens are important because they provide the first evidence relating to possible positional behaviors of Otavipithecus and the earliest fossil record of cercopithecoids from southern Africa. © 1996 Wiley-Liss, Inc.     

Caudal vertebral body articular surface morphology correlates with functional tail use in anthropoid primates

Prehensile tails, capable of suspending the entire body weight of an animal, have evolved in parallel in New World monkeys (Platyrrhini): once in the Atelinae (Alouatta, Ateles, Brachyteles, Lagothrix), and once in the Cebinae (Cebus, Sapajus). Structurally, the prehensile tails of atelines and cebines share morphological features that distinguish them from nonprehensile tails, including longer proximal tail regions, well‐developed hemal processes, robust caudal vertebrae resistant to higher torsional and bending stresses, and caudal musculature capable of producing higher contractile forces. The functional significance of shape variation in the articular surfaces of caudal vertebral bodies, however, is relatively less well understood. Given that tail use differs considerably among prehensile and nonprehensile anthropoids, it is reasonable to predict that caudal vertebral body articular surface area and shape will respond to use‐specific patterns of mechanical loading. We examine the potential for intervertebral articular surface contour curvature and relative surface area to discriminate between prehensile‐tailed and nonprehensile‐tailed platyrrhines and cercopithecoids. The proximal and distal intervertebral articular surfaces of the first (Ca1), transitional and longest caudal vertebrae were examined for individuals representing 10 anthropoid taxa with differential patterns of tail‐use. Study results reveal significant morphological differences consistent with the functional demands of unique patterns of tail use for all vertebral elements sampled. Prehensile‐tailed platyrrhines that more frequently use their tails in suspension (atelines) had significantly larger and more convex intervertebral articular surfaces than all nonprehensile‐tailed anthropoids examined here, although the intervertebral articular surface contour curvatures of large, terrestrial cercopithecoids (i.e., Papio sp.) converge on the ateline condition. Prehensile‐tailed platyrrhines that more often use their tails in tripodal bracing postures (cebines) are morphologically intermediate between atelines and nonprehensile tailed anthropoids. J. Morphol. 275:1300–1311, 2014. © 2014 Wiley Periodicals, Inc.     

Functional morphology of the primate head and neck

The vertebral column plays a key role in maintaining posture, locomotion, and transmitting loads between body components. Cervical vertebrae act as a bridge between the torso and head and play a crucial role in the maintenance of head position and the visual field. Despite its importance in positional behaviors, the functional morphology of the cervical region remains poorly understood, particularly in comparison to the thoracic and lumbar sections of the spinal column. This study tests whether morphological variation in the primate cervical vertebrae correlates with differences in postural behavior. Phylogenetic generalized least-squares analyses were performed on a taxonomically broad sample of 26 extant primate taxa to test the link between vertebral morphology and posture. Kinematic data on primate head and neck postures were used instead of behavioral categories in an effort to provide a more direct analysis of our functional hypothesis. Results provide evidence for a function-form link between cervical vertebral shape and postural behaviors. Specifically, taxa with more pronograde heads and necks and less kyphotic orbits exhibit cervical vertebrae with longer spinous processes, indicating increased mechanical advantage for deep nuchal musculature, and craniocaudally longer vertebral bodies and more coronally oriented zygapophyseal articular facets, suggesting an emphasis on curve formation and maintenance within the cervical lordosis, coupled with a greater resistance to translation and ventral displacement. These results not only document support for functional relationships in cervical vertebrae features across a wide range of primate taxa, but highlight the utility of quantitative behavioral data in functional investigations. Am J Phys Anthropol 156:531–542, 2015. © 2015 Wiley Periodicals, Inc.     

Biomechanical allometry in hominoid thoracic vertebrae

Considerable differences in spinal morphology have been noted between humans and other hominoids. Although comparative analyses of the external morphology of vertebrae have been performed, much less is known regarding variations in internal morphology (density) and biomechanical performance among humans and closely related non-human primates. In the current study we utilize density calibrated computed tomography images of thoracic vertebral bodies from hominoids (n = 8-15 per species, human specimens 20-40 years of age) to obtain estimates of vertebral bone strength in axial compression and anteroposterior bending and to determine how estimates of strength scale with animal body mass. Our biomechanical analysis suggests that the strength of thoracic vertebral bodies is related to body mass (M) through power law relationships (y ∝ M^b) in which the exponent b is 0.89 (reduced major axis) for prediction of axial compressive strength and is equal to 1.89 (reduced major axis) for prediction of bending strength. No differences in the relationship between body mass and strength were observed among hominoids. However, thoracic vertebrae from humans were found to be disproportionately larger in terms of vertebral length (distance between cranial and caudal endplates) and overall vertebral body volume (p < 0.05). Additionally, vertebral bodies from humans were significantly less dense than in other hominoids (p < 0.05). We suggest that reduced density in human vertebral bodies is a result of a systemic increase in porosity of cancellous bone in humans, while increased vertebral body volume and length are a result of functional adaptation during growth resulting in a vertebral bone structure that is just as strong, relative to body mass, as in other hominoids.     

Identification and phyletic distribution of the plasma esterases of some anthropoid primates

Using electrophoresis, specific staining, and selective inhibition, we examined and identified esterase components in the plasma of 13 anthropoid species: 5 hominoids, 7 cercopithecoids, and 1 platyrrhine. Most species, unlike humans, exhibited one or more arylesterase and/or carboxylesterase components as well as cholinesterase and albumin-associated arylesterase. A distinctive arylesterase probably indicates pregnancy in cercopithecoids. While some characters (such as the net charge of the cholinesterase molecule) were extremely uniform across all taxa examined, other quantitative and qualitative traits showed intra- and interspecific variation. Comparison of a cladogram with the distribution of traits shows that the least phyletically stable traits are, in general, those that also exhibit intraspecific polymorphism. One genus-specific, and therefore relatively conservative, trait (weak dimer-dimer bonding in the cholinesterase molecule) evidently appeared independently among papionin cercopithecoids and hominoids. The most parsimonious interpretation of this distribution reinforces the notion of a Pan-Gorilla-Homoclade sororally related to Pongo.In general, plasma esterases are an underexploited source of genetic markers in primates.     

Morphology and Function of the Vertebral Column in Remingtonocetus domandaensis (Mammalia, Cetacea) from the Middle Eocene Domanda Formation of Pakistan

The archaeocete family Remingtonocetidae is a group of early cetaceans known from the Eocene of India and Pakistan. Previous studies of remingtonocetids focused primarily on cranial anatomy due to a paucity of well-preserved postcranial material. Here we describe the morphology of the known vertebral column in Remingtonocetus domandaensis based largely on a single well-preserved partial skeleton recovered from the upper Domanda Formation of Pakistan. The specimen preserves most of the precaudal vertebral column in articulation and includes seven complete cervical vertebrae, ten partial to complete thoracic vertebrae, six complete lumbar vertebrae, and the first three sacral vertebrae. Cervical centra are long and possess robust, imbricating transverse processes that stabilized the head and neck. Lumbar vertebrae allowed for limited flexibility and probably served primarily to stabilize the lumbar column during forceful retraction of the hind limbs. Vertebral evidence, taken together with pelvic and femoral morphology, is most consistent with interpretation of Remingtonocetus domandaensis as an animal that swam primarily by powerful movement of its hind limbs rather than dorsoventral undulation of its body axis.     

A calcaneus attributable to the primitive late eocene anthropoid Proteopithecus sylviae: Phenetic affinities and phylogenetic implications

A well‐preserved calcaneus referrable to Proteopithecus sylviae from the late Eocene Quarry L‐41 in the Fayum Depression, Egypt, provides new evidence relevant to this taxon's uncertain phylogenetic position. We assess morphological affinities of the new specimen using three‐dimensional geometric morphometric analyses with a comparative sample of primate calcanei representing major extinct and extant radiations (n = 58 genera, 106 specimens). Our analyses reveal that the calcaneal morphology of Proteopithecus is most similar to that of the younger Fayum parapithecid Apidium. Principal components analysis places Apidium and Proteopithecus in an intermediate position between primitive euprimates and crown anthropoids, based primarily on landmark configurations corresponding to moderate distal elongation, a more distal position of the peroneal tubercle, and a relatively “unflexed” calcaneal body. Proteopithecus and Apidium are similar to cercopithecoids and some omomyiforms in having an ectal facet that is more tightly curved, along with a larger degree of proximal calcaneal elongation, whereas other Fayum anthropoids, platyrrhines and adapiforms have a more open facet with less proximal elongation. The similarity to cercopithecoids is most plausibly interpreted as convergence given the less tightly curved ectal facets of stem catarrhines. The primary similarities between Proteopithecus and platyrrhines are mainly in the moderate distal elongation and the more distal position of the peroneal tubercle, both of which are not unique to these groups. Proteopithecus and Apidium exhibit derived anthropoid features, but also a suite of primitive retentions. The calcaneal morphology of Proteopithecus is consistent with our cladistic analysis, which places proteopithecids as a sister group of Parapithecoidea. Am J Phys Anthropol 151:372–397, 2013.© 2013 Wiley Periodicals, Inc.     

Radio-ulnar deviation of the primate carpus: an X-ray study

The lack of contact between the ulna and first row of carpals characterizes the wrist morphology of hominoids as compared to other primates. This distinctive feature--generally interpreted as a significant synapomorphy between humans and other hominoids--was a priori considered to be an indication of an increased capacity for ulnar deviation, allowing a greater diversity of hand movements. This X-ray study aimed to test this hypothesis by comparing the shifting of the carpals throughout radioulnar deviation in eight extant genera endowed with ulno-carpal contact or lacking it. The results show that the amplitude of ulnar deviation is not directly correlated with the presence or absence of an ulno-carpal contact: most ulnar deviation takes place at the antebrachio-carpal joint in those primates that lack an ulno-carpal contact (hominoids), instead of at the mid-carpal joint in primates whose ulna articulates with the triquetral (cercopithecoids, platyrrhines, most strepsirrhines). Analysis of the X-ray suggests that the loss of ulno-carpal contact improved the ability to supinate at the radio-ulnar joints, with correlated unfitness for palmigrade/semidigitigrade walking. This evolutive change, associated with a considerable reduction of the share of body weight carried on the forelimbs, likely cleared the way for either knuckle walking or bipedalism and handiness.     

Evolution of locomotion in Anthropoidea: the semicircular canal evidence

Our understanding of locomotor evolution in anthropoid primates has been limited to those taxa for which good postcranial fossil material and appropriate modern analogues are available. We report the results of an analysis of semicircular canal size variation in 16 fossil anthropoid species dating from the Late Eocene to the Late Miocene, and use these data to reconstruct evolutionary changes in locomotor adaptations in anthropoid primates over the last 35 Ma. Phylogenetically informed regression analyses of semicircular canal size reveal three important aspects of anthropoid locomotor evolution: (i) the earliest anthropoid primates engaged in relatively slow locomotor behaviours, suggesting that this was the basal anthropoid pattern; (ii) platyrrhines from the Miocene of South America were relatively agile compared with earlier anthropoids; and (iii) while the last common ancestor of cercopithecoids and hominoids likely was relatively slow like earlier stem catarrhines, the results suggest that the basal crown catarrhine may have been a relatively agile animal. The latter scenario would indicate that hominoids of the later Miocene secondarily derived their relatively slow locomotor repertoires.