Postcranial morphology and locomotion of the Eocene raoellid Indohyus (Artiodactyla: Mammalia)

Raoellids are small, raccoon-sized Eocene artiodactyls, closely related to archaic cetaceans (archaeocetes) that have poor representation of postcranial elements in the fossil record. Little is known of the aquatic and terrestrial locomotor affinities of raoellids due to the paucity of their fossil record, leaving a critical gap in our understanding of the earliest portion of the artiodactyl marine invasion. To address this gap, a comparative morphological analysis of the postcranial elements was undertaken based on newly recovered elements of the raoellid Indohyus, archaeocetes and extant artiodactyls. Greater than 200 postcranial elements of Indohyus were described, and some limb element cross-sections were visualised via paleohistological thin sections and CT scans. Results show that during terrestrial locomotion, Indohyus probably had a digitigrade posture and mediolaterally stabilised limbs that functioned mostly in flexion and extension within the parasagittal plane. Quantification of midshaft cross-sectional area for some elements of Indohyus showed an osteosclerotic cortex, a skeletal characteristic associated with aquatic behaviours. Indohyus may represent a critical intermediate in the evolution of the cetacean terrestrial-to-aquatic body plan, as it bears gracile postcranial element proportions similar to a terrestrial artiodactyl but also an incipient form of osteosclerosis compared to pakicetid archaeocetes.     

Dental metric comparisons of Morotopithecus and Afropithecus: implications for the validity of the genus Morotopithecus

Morotopithecus bishopi and Afropithecus turkanensis are two large-bodied hominoid primates from early Miocene deposits of eastern Africa. Researchers have used both cranial and postcranial characters to distinguish these two species. Unfortunately, of the fossil material attributed to each, only the face, palate, and upper dentition are preserved well enough in both species for direct comparisons. There are currently no known directly comparable postcranial elements. In this study, we reevaluated dental characters argued to distinguish the type specimens of Morotopithecus from Afropithecus: relative size of the upper premolars and M3. Exact randomization methods were used to address two questions. First, is it possible to find the degree of dental-size difference observed between Morotopithecus (UMP 62-11) and Afropithecus (KNM-WK 16999) within extant African hominoids? Second, what is the probability of observing the levels of difference found between the fossils among pairs of extant individuals? Metric differences in relative premolar and M3 size were calculated between all possible pairs within the extant sample and the observed difference of the fossil pair was then compared to the resulting distribution of extant pairs. The observed size differences for all comparisons in the fossil teeth were well within the variation observed in the extant African hominoid samples (p>0.05). In light of these results and other currently available cranial evidence, we suggest that the type specimens of Morotopithecus and Afropithecus are not different enough to support taxonomic distinction.     

Pierolapithecus and the functional morphology of Miocene ape hand phalanges: paleobiological and evolutionary implications

The partial skeleton of Pierolapithecus, which provides the oldest unequivocal evidence of orthogrady, together with the recently described phalanges from Pa?alar most likely attributable to Griphopithecus, provide a unique opportunity for understanding the changes in hand anatomy during the pronogrady/orthogrady transition in hominoid evolution. In this paper, we describe the Pierolapithecus hand phalanges and compare their morphology and proportions with those of other Miocene apes in order to make paleobiological inferences about locomotor evolution. In particular, we investigate the orthograde/pronograde evolutionary transition in order to test whether the acquisition of vertical climbing and suspension were decoupled during evolution. Our results indicate that the manual phalanges of Miocene apes are much more similar to one another than to living apes. In particular, Miocene apes retain primitive features related to powerful-grasping palmigrady on the basal portion, the shaft, and the trochlea of the proximal phalanges. These features suggest that above-branch quadrupedalism, inherited from stem hominoids, constituted a significant component of the locomotor repertories of different hominoid lineages at least until the late Miocene. Nonetheless, despite their striking morphological similarities, several Miocene apes do significantly differ in phalangeal curvature and/or elongation. Hispanopithecus most clearly departs by displaying markedly-curved and elongated phalanges, similar to those in the most suspensory of the extant apes (hylobatids and orangutans). This feature agrees with several others that indicate orang-like suspensory capabilities. The remaining Miocene apes, on the contrary, display low to moderate phalangeal curvature, and short to moderately-elongated phalanges, which are indicative of the lack of suspensory adaptations. As such, the transition from a pronograde towards an orthograde body plan, as far as this particular anatomical region is concerned, is reflected only in somewhat more elongated phalanges, which may be functionally related to enhanced vertical-climbing capabilities. Our results therefore agree with the view that hominoid locomotor evolution largely took place in a mosaic fashion: just as taillessness antedated the acquisition of an orthograde body plan, the emergence of the latter—being apparently related only to vertical climbing—also preceded the acquisition of suspensory adaptations, as well as the loss of primitively-retained, palmigrady-related features.     

A reassessment of living hominoid postcranial variability: implications for ape evolution

In an analysis of hominoid postcranial variation, 'Evol. Anthrop. 6 (1998) 87' argued that many purportedly unique features of the hominoid postcranium are actually much more variable than previously reported and in many instances overlap with both suspensory (Ateles) and non-suspensory primates. Based on these results, it was concluded that parallelism in the living ape postcranium was a plausible and even likely possibility given the Miocene hominoid postcranial record. However, this analysis did not distinguish whether within-hominoid variability or overlap with non-hominoids involved one or all ape taxa, a distinction which has potentially important effects on the interpretation of results. To address this issue, primate postcranial morphometric data from the trunk and forelimb were reanalyzed using three techniques: cladistic analysis, principle components analysis, and cluster analysis. Results reveal that these postcranial characters distinguish not only suspensory and quadrupedal primates but also discriminate hominoids and Ateles from all other taxa, great apes from lesser apes and Ateles, cercopithecines from colobines, and cercopithecoids from platyrrhines. The majority of hominoid variability and overlap with Ateles occurs with Hylobates humeral head and shoulder joint characters related to brachiation. This suggests that Hylobates' specializations may skew analyses of hominoid postcranial uniqueness and variability, and that great apes are relatively similar in their postcranium.     

Analysis of the human and ape foot during bipedal standing with implications for the evolution of the foot

The ratio of the power arm (the distance from the heel to the talocrural joint) to the load arm (that from the talocrural joint to the distal head of the metatarsals), or RPL, differs markedly between the human and ape foot. The arches are relatively higher in the human foot in comparison with those in apes. This study evaluates the effect of these two differences on biomechanical effectiveness during bipedal standing, estimating the forces acting across the talocrural and tarsometatarsal joints, and attempts to identify which type of foot is optimal for bipedal standing. A simple model of the foot musculoskeletal system was built to represent the geometric and force relationships in the foot during bipedal standing, and measurements for a variety of human and ape feet applied. The results show that: (1) an RPL of around 40% (as is the case in the human foot) minimizes required muscle force at the talocrural joint; (2) the presence of an high arch in the human foot reduces forces in the plantar musculature and aponeurosis; and (3) the human foot has a lower total of force in joints and muscles than do the ape feet. These results indicate that the proportions of the human foot, and the height of the medial arch are indeed better optimized for bipedal standing than those of apes, further suggesting that their current state is to some extent the product of positive selection for enhanced bipedal standing during the evolution of the foot.     

Postcranial remains and the origin of modern humans

The nature, timing, and location of the origin of modern humans has been the subject of intense controversy for the last 15 years.^1–4 Genetic data and new radiometric dates for key fossils that lie beyond the range of radiocarbon dating have substantially added to the knowledge derived from the fossil evidence documenting the transition from archaic to modern humans. These new data, however, have failed to resolve the problem in its entirety. Most authorities now accept that Africa played an important, and probably central, role in the origin of modern humans.^7–13 The genetic evidence seems to be particularly emphatic that an African population that existed between 200,000 and 100,000 years ago (100 ka) is ancestral to all living humans.^6,7 Controversy still surrounds the question of how much, if at all, archaic humans from outside of Africa, such as Neandertals, late archaic Chinese hominins such as Jinniushan, and the Indonesian Ngandong hominins, may have contributed to the morphological and genetic diversity present in living populations and the morphology of the earliest fossils of modern humans.¹⁰     

Habits, functional morphology and the evolution of pycnogonids

Recent work on functional morphology has revealed not only how a wide range of animals work, but shows the significance of their shapes in great detail. Also, sound evidence of evolution is provided. A new approach towards the understanding of Pycnogonida comes from an appreciation of the significance of their general habits and shapes and from the structure and mode of action of their legs. Recent fossil evidence shows that the arachnids had at least two terrestrial landings, occurring millions of years apart in time. At least two, but probably more, separate arachnid lines lived in the sea. It is concluded that pycnogonids evolved from one such aquatic group which never became terrestrial.     

Understanding hind limb weight support in chimpanzees with implications for the evolution of primate locomotion

Most quadrupedal mammals support a larger amount of body weight on their forelimbs compared with their hind limbs during locomotion, whereas most primates support more of their body weight on their hind limbs. Increased hind limb weight support is generally interpreted as an adaptation that reduces stress on primates' highly mobile forelimb joints. Thus, increased hind limb weight support was likely vital for the evolution of primate arboreality. Despite its evolutionary importance, the mechanism used by primates to achieve this important kinetic pattern remains unclear. Here, we examine weight support patterns in a sample of chimpanzees (Pan troglodytes) to test the hypothesis that limb position, combined with whole body center of mass position (COM), explains increased hind limb weight support in this taxon. Chimpanzees have a COM midway between their shoulders and hips and walk with a relatively protracted hind limb and a relatively vertical forelimb, averaged over a step. Thus, the limb kinematics of chimpanzees brings their feet closer to the COM than their hands, generating greater hind limb weight support. Comparative data suggest that these same factors likely explain weight support patterns for a broader sample of primates. It remains unclear whether primates use these limb kinematics to increase hind limb weight support, or whether they are byproducts of other gait characteristics. The latter hypothesis raises the intriguing possibility that primate weight support patterns actually evolved as byproducts of other traits, or spandrels, rather than as adaptations to increase forelimb mobility. Am J Phys Anthropol, 2009. © 2008 Wiley‐Liss, Inc.     

Arboreal bipedalism in wild chimpanzees: implications for the evolution of hominid posture and locomotion

Field observations of bipedal posture and locomotion in wild chimpanzees (Pan troglodytes) can serve as key evidence for reconstructing the likely origins of bipedalism in the last prehominid human ancestor. This paper reports on a sample of bipedal bouts, recorded ad libitum, in wild chimpanzees in Bwindi Impenetrable National Park in southwestern Uganda. The Ruhija community of chimpanzees in Bwindi displays a high rate of bipedal posture. In 246.7 hr of observation from 2001-2003, 179 instances of bipedal posture lasting 5 sec or longer were recorded, for a rate of 0.73 bouts per observation hour. Bipedalism was observed only on arboreal substrates, and was almost all postural, and not locomotor. Bipedalism was part of a complex series of positional behaviors related to feeding, which included two-legged standing, one-legged standing with arm support, and other intermediate postures. Ninety-six percent of bipedal bouts occurred in a foraging context, always as a chimpanzee reached to pluck fruit from tree limbs. Bipedalism was seen in both male and female adults, less frequently among juveniles, and rarely in infants. Both the frequency and duration of bipedal bouts showed a significant positive correlation with estimated substrate diameter. Neither fruit size nor nearest-neighbor association patterns were significantly correlated with the occurrence of bipedalism. Bipedalism is seen frequently in the Bwindi chimpanzee community, in part because of the unusual observer conditions at Bwindi. Most observations of bipedalism were made when the animals were in treetops and the observer at eye-level across narrow ravines. This suggests that wild chimpanzees may engage in bipedal behavior more often than is generally appreciated. Models of the likely evolutionary origins of bipedalism are considered in the light of Bwindi bipedalism data. Bipedalism among Bwindi chimpanzees suggests the origin of bipedal posture in hominids to be related to foraging advantages in fruit trees. It suggests important arboreal advantages in upright posture. The origin of postural bipedalism may have preceded and been causally disconnected from locomotor bipedalism.     

Bipedal locomotion as a feeding adaptation in gelada baboons,and its implications for hominid evolution

Bipedal locomotion by gelada baboons is used for travelling between adjacent feeding sites. The same could be true of its origins in man.     

Postcranial morphology and the locomotor habits of living and extinct carnivorans

Members of the order Carnivora display a broad range of locomotor habits, including cursorial, scansorial, arboreal, semiaquatic, aquatic, and semifossorial species from multiple families. Ecomorphological analyses from osteological measurements have been used successfully in prior studies of carnivorans and rodents to accurately infer the locomotor habits of extinct species. This study uses 20 postcranial measurements that have been shown to be effective indicators of locomotor habits in rodents and incorporates an extensive sample of over 300 individuals from more than 100 living carnivoran species. We performed statistical analyses, including analysis of variance (ANOVA) and stepwise discriminant function analysis, using a set of 16 functional indices (ratios). Our ANOVA results reveal consistent differences in postcranial skeletal morphology among locomotor groups. Cursorial species display distal elongation of the limbs, gracile limb elements, and relatively narrow humeral and femoral epicondyles. Aquatic and semiaquatic species display relatively robust, shortened femora and elongate metatarsals. Semifossorial species display relatively short, robust limbs with enlarged muscular attachment sites and elongate claws. Both semiaquatic and semifossorial species have relatively elongate olecranon process of the ulna and enlarged humeral and femoral epicondyles. Terrestrial, scansorial, and arboreal species are characterized by having primarily intermediate features, but arboreal species do show relatively elongate manual digits. Morphological indices effectively discriminate locomotor groups, with cursorial and arboreal species more accurately classified than terrestrial, scansorial, or semiaquatic species. Both within and between families, species with similar locomotor habits converge toward similar postcranial morphology despite their independent evolutionary histories. The discriminant analysis worked particularly well to correctly classify members of the Canidae, but not as well for members of the Mustelidae or Ursidae. Results are used to infer the locomotor habits of extinct carnivorans, including members of several extinct families, and also 12 species from the Pleistocene of Rancho La Brea. J. Morphol., 2013. © 2012 Wiley Periodicals, Inc.     

Postcranial morphology,functional adaptations and palaeobiology of Callistoe vincei,a predaceous metatherian from the Eocene of Salta,north‐western Argentina

Abstract: Callistoe vincei Babot et al., 2002 is a Paleogene borhyaenoid known from exceptionally complete postcranial elements, which provides rare information about the anatomy and evolutionary history of metatherian predators during the South American Cenozoic. The axial skeleton of Callistoe is characterized by the peculiar transverse processes of the cervical vertebrae emphasizing lateral instead of sagittal traction. There is no clavicle and eighteen thoracolumbar vertebrae, of which only five are lumbars. The shoulder and elbow joints suggest movements restricted to parasagittal flexion/extension that are consistent with primarily terrestrial locomotion, as is also emphasized in Borhyaena tuberata and Lycopsis longirostrus. On the manus, the pollex is not reduced and the ungual phalanges indicate very long claws, similar to those observed in some extant digging taxa. This feature is unique to C. vincei among borhyaenoids. The knee joint is characterized by the presence of ossified patellae but shallow femoral trochleae. This joint suggests that the leg was nearly parasagittal, a position also inferred for Borhyaena. The astragalus shape is consistent with parasagittal flexion/extension, as in all Miocene–Pliocene borhyaenoids. The hind foot is characterized by reduced claws in comparison with the manus as well as the slenderness of the first and fifth digits, another peculiarity of C. vincei. The habitat of Callistoe was a temperate humid forest and according to the known fossil record, Callistoe was the largest mammalian predator of its time, sharing the predator ecological niche with crocodiles.     

Feeding behavior, diet, and the functional consequences of jaw form in orangutans, with implications for the evolution of Pongo

Orangutans are amongst the most craniometrically variable of the extant great apes, yet there has been no attempt to explicitly link this morphological variation with observed differences in behavioral ecology. This study explores the relationship between feeding behavior, diet, and mandibular morphology in orangutans. All orangutans prefer ripe, pulpy fruit when available. However, some populations of Bornean orangutans (Pongo pygmaeus morio and P. p. wurmbii) rely more heavily on bark and relatively tough vegetation during periods of low fruit yield than do Sumatran orangutans (Pongo abelii). I tested the hypothesis that Bornean orangutans exhibit structural features of the mandible that provide greater load resistance abilities to masticatory and incisal forces. Compared to P. abelii, P. p. morio exhibits greater load resistance abilities as reflected in a relatively deeper mandibular corpus, deeper and wider mandibular symphysis, and relatively greater condylar area. P. p. wurmbii exhibits most of these same morphologies, and in all comparisons is either comparable in jaw proportions to P. p. morio, or intermediate between P. p. morio and P. abelii. These data indicate that P. p. morio and P. p. wurmbii are better suited to resisting large and/or frequent jaw loads than P. abelii. Using these results, I evaluated mandibular morphology in P. p. pygmaeus, a Bornean orangutan population whose behavioral ecology is poorly known. Pongo p. pygmaeus generally exhibits relatively greater load resistance capabilities than P. abelii, but less than P. p. morio. These results suggest that P. p. pygmaeus may consume greater amounts of tougher and/or more obdurate foods than P. abelii, and that consumption of such foods may intensify amongst Bornean orangutan populations. Finally, data from this study are used to evaluate variation in craniomandibular morphology in Khoratpithecus piriyai, possibly the earliest relative of Pongo from the late Miocene of Thailand, and the late Pleistocene Hoa Binh subfossil orangutan recovered from Vietnam. With the exception of a relatively thicker M(3) mandibular corpus, K. piriyai has jaw proportions that would be expected for an extant orangutan of comparable jaw size. Likewise, the Hoa Binh subfossil does not differ in skull proportions from extant Pongo, independent of the effects of increase in jaw size. These results indicate that differences in skull and mandibular proportions between these fossil and subfossil orangutans and extant Pongo are allometric. Furthermore, the ability of K. piriyai to resist jaw loads appears to have been comparable to that of extant orangutans. However, the similarity in jaw proportions between P. abelii and K. piriyai suggest the latter may have been dietarily more similar to Sumatran orangutans.     

The eloquent ape: genes, brains and the evolution of language

The human capacity to acquire complex language seems to be without parallel in the natural world. The origins of this remarkable trait have long resisted adequate explanation, but advances in fields that range from molecular genetics to cognitive neuroscience offer new promise. Here we synthesize recent developments in linguistics, psychology and neuroimaging with progress in comparative genomics, gene-expression profiling and studies of developmental disorders. We argue that language should be viewed not as a wholesale innovation, but as a complex reconfiguration of ancestral systems that have been adapted in evolutionarily novel ways.     

Molecular phylogenetics of the siphonophora (Cnidaria), with implications for the evolution of functional specialization

Siphonophores are a group of pelagic colonial hydrozoans (Cnidaria) that have long been of general interest because of the division of labor between the polyps and medusae that make up these "superorganisms." These polyps and medusae are each homologous to free living animals but are generated by an incomplete asexual budding process that leaves them physiologically integrated. They are functionally specialized for different tasks and are precisely organized within each colony. The number of functional types of polyps and medusae varies across taxa, and different authors have used this character to construct phylogenies polarized in opposite directions, depending on whether they thought siphonophore evolution proceeded by a reduction or an increase in functional specialization. We have collected taxa across all major groups of siphonophores, many of which are found exclusively in the deep sea, using remotely operated underwater vehicles (ROVs) and by SCUBA diving from ships in the open ocean. We have used 52 siphonophores and four outgroup taxa to estimate the siphonophore phylogeny with molecular data from the nuclear small subunit ribosomal RNA gene (18S) and the mitochondrial large subunit ribosomal RNA gene (16S). Parsimony reconstructions indicate that functionally specialized polyps and medusae have been gained and lost across the phylogeny. Maximum likelihood and Bayesian analyses of morphological data suggest that the transition rate for decreased functional specialization is greater than the transition rate for increased functional specialization for three out of the four investigated categories of polyps and medusae. The present analysis also bears on several long-standing questions about siphonophore systematics. It indicates that the cystonects are sister to all other siphonophores, a group that we call the Codonophora. We also find that the Calycophorae are nested within the Physonectae, and that the Brachystelia, a historically recognized grouping of short-stemmed taxa, are polyphyletic. [Cnidaria; colonial animals; deep sea; division of labor; functional specialization; Hydrozoa; phylogenetics; Siphonophores.].     

South Amerindian craniofacial morphology: diversity and implications for Amerindian evolution

The most compelling models concerning the peopling of the Americas consider that modern Amerindians share a common biological pattern, showing affinities with populations of the Asian Northeast. The aim of the present study was to assess the degree of variation of craniofacial morphology of South American Amerindians in a worldwide context. Forty-three linear variables were analyzed on crania derived from American, Asian, Australo-Melanesian, European, South-Saharan African, and Polynesian regions. South America was represented by seven Amerindian samples. In order to understand morphologic diversity among Amerindians of South America, variation was estimated using regions and local populations as units of analysis. Variances and F(ST) values were calculated for each unit, respectively. Both analyses indicated that morphologic variation in Southern Amerindians is extremely high: an F(ST) of 0.01531 was obtained for Southern Amerindians, and values from 0.0371-0.1205 for other world regions. Some aspects linked to the time and mode of the peopling of the Americas and various microevolutionary processes undergone by Amerindians are discussed. Some of the alternatives proposed to explain this high variation include: a greater antiquity of the peopling than what is mostly accepted, a peopling by several highly differentiated waves, an important effect of genetic drift, and gene flow with Paleoamericans. A combination of some of these alternatives explains at least some of the variation.     

The correspondence between proximal phalanx morphology and locomotion: implications for inferring the locomotor behavior of fossil catarrhines

Phalanges are considered to be highly informative in the reconstruction of extinct primate locomotor behavior since these skeletal elements directly interact with the substrate during locomotion. Variation in shaft curvature and relative phalangeal length has been linked to differences in the degree of suspension and overall arboreal locomotor activities. Building on previous work, this study investigated these two skeletal characters in a comparative context to analyze function, while taking evolutionary relationships into account. This study examined the correspondence between proportions of suspension and overall substrate usage observed in 17 extant taxa and included angle of curvature and relative phalangeal length. Predictive models based on these traits are reported. Published proportions of different locomotor behaviors were regressed against each phalangeal measurement and a size proxy. The relationship between each behavior and skeletal trait was investigated using ordinary least-squares, phylogenetic generalized least-squares (pGLS), and two pGLS transformation methods to determine the model of best-fit. Phalangeal curvature and relative length had significant positive relationships with both suspension and overall arboreal locomotion. Cross-validation analyses demonstrated that relative length and curvature provide accurate predictions of relative suspensory behavior and substrate usage in a range of extant species when used together in predictive models. These regression equations provide a refined method to assess the amount of suspensory and overall arboreal locomotion characterizing species in the catarrhine fossil record.