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Long bone articular and diaphyseal structure in Old World monkeys and apes. II: Estimation of body mass.

Body mass estimation equations are generated from long bone cross-sectional diaphyseal and articular surface dimensions in 176 individuals and 12 species of hominoids and cercopithecoids. A series of comparisons is carried out to determine the best body mass predictors for each of several taxonomic/locomotor groupings. Articular breadths are better predictors than articular surface areas, while cross-sectional shaft strengths are better predictors than shaft external breadths. Percent standard errors of estimate (%SEEs) and percent prediction errors for most of the better predictors range between 10-20%. Confidence intervals of equations using sex/species means are fairly representative of those calculated using individual data, except for sex/species means equations with very low %SEEs (under about 10%), where confidence intervals (CIs) based on individuals are likely to be larger. Given individual variability, or biological "error," this may represent a lower limit of precision in estimating individual body masses. In general, it is much more preferable to determine at least broad locomotor affinities, and thus appropriate modern reference groups, before applying body mass estimation equations. However, some structural dimensions are less sensitive to locomotor distinctions than others; for example, proximal tibial articular M-L breadth is apparently "locomotor blind" regarding body mass estimation within the present study sample. In other cases where locomotor affiliation is uncertain, mean estimates from different reference groups can be used, while for some dimensions no estimation should be attempted. The techniques are illustrated by estimating the body masses of four fossil anthropoid specimens of Proconsul nyanzae, Proconsul heseloni, Morotopithecus bishopi, and Theropithecus oswaldi.

Animals↗

Taxonomic affinities of the Eppelsheim femur.

The taxonomic affinities of the Eppelsheim femur, known as Paidopithex, have been unclear for more than a century. Over the years, due to similarities with Pliopithecus, some authors have considered it a large pliopithecid, while others refer to it as Dryopithecus. The issue could not be resolved, because no definitive Dryopithecus femora were available. With the discovery of the Dryopithecus laietanus skeleton from Can Llobateres (CLl 18800), it has become possible to test the attribution of the Eppelsheim femur to Dryopithecus on the basis of direct morphological and metrical comparisons. By means of allometric techniques, we show that the Eppelsheim and D. laietanus femora fit different hindlimb morphologies with regard to relative length and relative head/neck size, with Paidopithex significantly differing from Dryopithecus, but more closely resembling Pliopithecus. Paidopithex also differs from Dryopithecus in other important aspects, such as its lower neck/shaft angle, lack of elevation of the femoral head above the greater trochanter, more posteriorly oriented lesser trochanter, and proximal shaft diameter thicker anteroposteriorly than mediolaterally. In these features, Paidopithex most closely resembles Pliopithecus in spite of differences in body mass (ca. 22 kg vs. ca. 10 kg, respectively). These features suggest that Paidopithex used a primitive locomotor pattern associated with arboreal quadrupedalism, instead of the more derived pattern displayed by Dryopithecus. Currently available evidence confirms that the attribution of Paidopithex to Dryopithecus can be rejected. Paidopithex could be a large and otherwise unknown pliopithecid, but the possibility cannot be ruled out that it represents a third kind of catarrhine.

Animals↗

Integration, phylogeny, and the hominid cranial base.

Basicranial features were examined in catarrhine primates and early hominids in order to demonstrate how information about morphological integration can be incorporated into phylogenetic analysis. Hypotheses purporting to explain the functional and structural relationships of basicranial characters were tested using factor analysis. Characters found to be functionally or structurally related to each other were then further examined in order to determine whether there was evidence that they were phylogenetically independent. If phylogenetic independence could not be demonstrated, then the characters were presumed to be integrated and were grouped into a complex. That complex was then treated as if it were a single character for the purposes of cladistic analysis. Factor analysis revealed that five basicranial features may be structurally related to relative brain size in hominoids. Depending on how one defines phylogenetic independence, as few as two, or as many as all of those characters might be morphologically integrated. A cladistic analysis of early hominids based on basicranial features revealed that the use of integrated complexes had a substantial effect on the phylogenetic position of Australopithecus africanus, a species whose relationships are poorly resolved. Moreover, the use of complexes also had an effect on reanalyses of certain published cladistic data sets, implying that those studies might have been biased by patterns of basicranial integration. These results demonstrate that patterns of morphological integration need to be considered carefully in all morphology-based cladistic analyses, regardless of taxon or anatomical focus. However, an important caveat is that the functional and structural hypotheses tested here predicted much higher degrees of integration than were observed. This result warns strongly that hypotheses of integration must be tested before they can be adequately employed in phylogenetic analysis. The uncritical acceptance of an untested hypothesis of integration is likely to be as disruptive to a cladistic analysis as when integration is ignored.

Animals↗

Egarapithecus narcisoi, a new genus of Pliopithecidae (primates, catarrhini) from the Late Miocene of Spain.

Pliopithecid remains from the Spanish locality of Torrent de Febulines (Late Vallesian, MN 10), consisting of right and left mandibular fragments with partial tooth rows and an isolated P(3) probably belonging to the same individual, are described and assigned to Egarapithecus narcisoi gen. et sp. nov. (Pliopithecidae, Crouzeliinae). This is a highly derived species dated at around 9 Ma (Ma = 10(6) years), representing the latest appearance of the family in the European continent. Morphologically it is the most distant member from the inferred primitive pliopithecid morphotype, displaying many autapomorphies that notably accentuate those of the remaining Crouzeliinae. A cladistic analysis based on lower cheek teeth, performed in order to tentatively assess the phylogenetic relationships of Egarapithecus within the Crouzeliinae, indicates that several equally parsimonious cladograms are possible in the light of current evidence. This is due to uncertainties regarding the position of Plesiopliopithecus and Crouzelia (here considered distinct genera), as a result of missing characters and the significant degree of homoplasy apparently involved in crouzeliine dental evolution. Whether Egarapithecus is more closely related to Crouzelia or to Anapithecus (the latter hypothesis tentatively favored here) cannot be definitively resolved with the currently available material and deserves further investigation. It is clear, however, that Egarapithecus is one of the more derived and specialized members of the Pliopithecidae.

Animals↗

Allometry of primate hair density and the evolution of human hairlessness.

Allometric analyses of hair densities in 23 anthropoid primate taxa reveal that increasingly massive primates have systematically fewer hairs per equal unit of body surface. Considering the absence of effective sweating in monkeys and apes, the negative allometry of relative hair density may represent an architectural adaptation to thermal constraints imposed by the decreasing ratios of surface area to volume in progressively massive primates. Judging by estimates of body volume, denudation of the earliest hominids should have progressed to a considerable extent prior to their shift from a forest to a grassland habitat during the Pliocene. We propose that, lacking a reflective coat of hair, the exploitation of eccrine sweating emerged as the primary mechanism for adaptation to the increased heat leads of man's new environment and permitted further reduction of the remnant coat to its present vestigial condition.

Animals↗

Sexual dimorphism and allometry in primate ossa coxae.

Five measurements were taken on the ossa coxae of 454 adult primates representing Ceboidea, Cercopithecoidea and Hominoidea. Sex differences in these variables and their relationships to overall body size and sexual dimorphism were tested by means of Student's T-test and regression analysis. The study attempts to clarify the nature of primate pelvic sexual dimorphism, including allometric effects, and more specifically, test the assertion made by Mobb and Wood (1977) that sexual dimorphism in body size in not an important determinant in pelvic sex differences. Variables that contribute to the size of the birth canal tend to be larger in females than males in all taxa studied except two. In these, Hylobates and Alouatta, there were no significant differences between the sexes for any of the five variables. In general, sexual dimorphism in variables contributing to the size of the birth canal was correlated (r approximately or equal to 0.8) with sexual dimorphism in body size. Furthermore, the coefficients of allometry underlying pelvic sex differences were shown to be moderately correlated (r approximately or equal to 0.5) with sexual dimorphism in size. The influence of other adaptive factors on primate pelvic sexual dimorphism are also briefly discussed.

Animals↗

The morphology and wear of the lingual notch in macaques and langurs.

Although interspecific differences in the relative development of molar occlusal features have been documented for most primate species, wear-related changes in these features are only beginning to be understood. In the present study, the notch between the metaconid and entoconid of M2 was examined in a skeletal sample of Macaca fascicularis, presbytis cristatus, and Presbytis rubicunda from the Museum of Comparative Zoology at Harvard University. Photogrammetric analyses yielded X, Y, and Z coordinates that were used to compute three angular measurements and two length measurements at the lingual notch. Statistical analyses of measurements from unworn dentitions indicated that the mesial slope of the entoconid is steeper than the distal slope of the metaconid in all three species. In addition, interspecific comparisons demonstrated that P. cristatus has the steepest lingual notch bordered by the largest molar shearing crests, while P. rubicunda and M. fascicularis have molar shearing crests of similar size, with P. rubicunda merely having higher cusps that are closer together than those of M. fascicularis. Finally, P. cristatus shows a smaller decrease in lingual cusp relief with wear than M. fascicularis, while P. cristatus and P. rubicunda probably show similar decreases in lingual cusp relief with wear. The differences in wear-related changes in lingual cusp relief between M. fascicularis and P. cristatus may well be related to the frugivorous/folivorous dietary differences between these species.

Animals↗

Ontogenetic and interspecific organ weight allometry in Old World monkeys.

The importance of allometry as an analytic tool is well recognized in the literature of primate morphology. However, a number of recent studies have illustrated how interpretive difficulties can arise when researchers confound different types of allometric data. Such confusion is due less to carelessness than to uncertainty about how different types of allometry are related. The present study examines the relationship between two types--ontogenetic and interspecific allometry--in the case of organ weight scaling in six species of Old World monkeys. Accepting the interpretation of interspecific allometry as a reflection of functional scaling constraints, the results of this analysis indicate how ontogenetic patterns have been modified in different-sized species to maintain compliance with these constraints. Specifically, for the heart and lungs it appears that vertical transpositions of individual species' ontogenies are dictated by isometric interspecific allometry, while in the case of the kidneys and liver, the relation of negative allometry across species entails alteration of the relative growth coefficients of the individual species. While these conclusions can at present only be applied to organ weight scaling, the approach of examining interspecific patterns in light of developmental differences between species should prove very helpful in our efforts to understand the phenomena of size and scaling.

Aging↗

Distribution of enamel on the incisors of Old World monkeys.

Longitudinal ground sections of 29 Old World monkey central lower incisors were studied histologically and metrically. Labiolingual incisor width tended to scale isometrically with body weight but with important deviations in relative incisor size, which appeared to be correlated with diet in accord with work by Hylander. Lower incisors of the predominantly folivorous colobine monkeys had a substantial layer of enamel on both lingual and labial aspects and consequently had blunt incisal edges. These teeth in both cercopithecins and papionins, which are omnivorous or frugivorous, had little or no enamel on the lingual aspect, resulting in sharp incisal edges. It is suggested that colobine incisors are used mainly in gripping and tearing leaves, whereas cercopithecine incisors are better adapted to cutting and scraping. Crown height showed a positive allometric relationship with overall incisor height, so that the tall incisors of papionins, especially Papio and Mandrillus, were more hypsodont than the shorter incisors of colobines and cercopithecins. This appears to be related to differences in the rates of incisor wear between the groups.

Animals↗

Nut-like oil seeds: food for monkeys, chimpanzees, humans, and probably ape-men.

The hypothetical hyperrobust australopithecine gnathic nutcracker adaptation is reexamined in light of ecobotanical information on edible wild nuts provided by the flora of tropical and subtropical Africa. The nut producing species are tree-forms. Those of the forest region do not as a rule produce fruits with edible mesocarps. In contrast, the woodland savanna species (particularly in the Zambezian region) characteristically provide an important whole fruit, i.e., a nutritious mesocarp in addition to edible oil-rich nut seeds. These fruits drop from the tree before they are fully mature and go through the final ripening phase on the ground. They are important seasonal foods for a variety of vertebrates, including primates, elephants, and antelope. Altogether the nuts exhibit a broad range of toughness values, measured here as strength under compression. The woodland nuts are not as tough (177-934 kg force, breaking load) as those of the tropical forest (192-1,673 kg force). The seed-predators of the woodland species include squirrels, baboons, warthogs, and parrots. Paleoecological analyses indicate that it was the woodland nuts that were probably available to Australopithecus boisei and A. robustus. Preliminary estimates of adult male gnathic nut-cracking capabilities suggest that A. boisei could have orally cracked a significant portion of the woodland nuts. In spite of this, ecobotanical data indicate that we can probably reject the hypothesis that these hominids were year-round gnathic nut-cracking specialists. Both the indirect and direct evidence support this conclusion.

Africa↗

Seed-eating by West African cercopithecines, with reference to the possible evolution of bilophodont molars.

Data on tooth use in eating fruits and seeds were collected on 12 West African monkeys representing five species of cercopithecines, Cercopithecus aethiops, Cercopithecus campbelli, Cercocebus atys, Erythrocebus patas, and Papio papio. Field observations and information in the published literature were used to select fruits for captive feeding trials. A total of over 27,000 tests were conducted to determine the preferences of the monkeys for 78 fruits. Data were collected on the selection of fruit parts, as well as tooth use, in eating 88 fruit species. All five monkey species had remarkably similar fruit part preferences. Seeds were eaten in 86% of the tested fruits and represent the fruit part most frequently eaten by all the tested monkeys. With few exceptions, molars were used to puncture and crush the seeds. It is suggested that the development of bilophodont molars might be an adaptation by Old World monkeys to seed predation. Given their large size relative to other arboreal frugivores, seed predation could provide a dietary niche for Old World monkeys.

Adaptation, Physiological↗

Absence of strongly kin-preferential behavior by adult female sooty mangabeys (Cercocebus atys).

The objective of this study was to test the hypothesis that kin-preferential behavior would be present in sooty mangabeys (Cercocebus atys), a species taxonomically close to baboons and macaques. The affiliative behavior of the adult female members of a large captive group of these mangabeys was analyzed to test this prediction. These females groomed, were approached by, were in proximity to, and were in contact with their kin significantly more than expected, but only when all kin were included in the analysis. Removal of only the mother-infant (less than 1 year) dyadic interactions removed all significant kin effects. Kin-preferential behavior was also absent in affiliative interactions among the adult females as a class. Affiliation between mothers and offspring significantly exceeded that for all other kinship categories (such as siblings, etc.), and affiliation with kin other than offspring did not differ from that with nonkin adults. In their interactions with nonkin, the adult females showed some preference (duration of grooming) for those adult females of similar age, an effect predicted by the intensity of interaction among members of the same age cohort during development. These similar-aged females may also be paternally related. In comparing these results with the existing literature on kin-preferential behavior, two conclusions may be reached: (1) age and degree of kinship are primary factors that must be considered in order to avoid the existing overgeneralization of the importance of kinship in primate social organization, and (2) the role and importance of affiliative behavior in kin-selection theory should perhaps be re-examined in light of questions raised by this study.

Animals↗

Functional assessment of subfamily variation in maxillomandibular morphology among Old World monkeys.

Among Old World monkeys, subfamily variation in maxillomandibular form is commonly attributed to divergent dietary and social behaviors. However, our knowledge of any musculoskeletal adaptations for gape in cercopithecines, and folivory in colobines, is incomplete. Such data are requisite to a more informed perspective on the evolutionary morphology of these taxa. Structural analyses of gape and biomechanical efficiency were applied to a representative sample of adult cercopithecids. Factors pertaining to the biomechanical scaling of cranial structures were evaluated with least-squares bivariate regression techniques. To assess subfamily differences in masticatory efficiency, analyses of covariance were made between relevant factors. Cercopithecines achieve increased gape and relative canine size mainly with strong positive allometry of the facial skull, combined with a larger gonial angle. Colobines possess a relatively long masseter lever arm and short facial skull, as well as an enlargened masseter-medial pterygoid complex. Subfamily differences in temporalis lever arm scaling are negligible. Biomechanical comparisons within and between subfamilies suggest that the mechanical advantage of the temporalis is relatively greater than that of the masseter, while the mechanical advantage of both muscles increases with face length. Evidence is presented to stress the need for adequate consideration of the dependent variable in allometric investigations of skull form.

Analysis of Variance↗

Comparison of muscle weight and force ratios in New and Old World monkeys.

Thin mandibles and small incisors found in New World monkeys as compared with Old World monkeys suggest that there may be differences in craniofacial loading patterns between these two groups, particularly in levels of mandibular corpus twisting (Hylander, 1975, 1979a; Eaglen, 1984; Bouvier, 1986a,b). This study examined the hypothesis that changes in the relative force contributions of the masticatory muscles were responsible for lowering torsion on the mandibular corpus in New World monkeys. Muscle weight and physiological cross-sections were compared using data from the literature (Schumacher, 1960: Turnbull, 1970; Cachel, 1979) as well as new data on adult male Cebus apella and Macaca mulatta. Both age and sex had an effect on muscle ratios. Mixed samples such as those used by Schumacher and Turnbull probably are not appropriate for drawing conclusions concerning species or group differences in muscle ratios. In addition, biomechanical conclusions based on muscle weight ratios alone to estimate muscle force may be misleading because fiber length inversely affects the amount of force a muscle can exert. A comparison of ratios based on physiological cross-section as an estimator of muscle force in New and Old World monkeys does not support the hypothesis that alterations in force contribution by individual masticatory muscles are responsible for minimizing mandibular corpus twisting in New World monkeys. Therefore, if twisting has been minimized in New World monkeys as suggested by their thin corpora, other changes in the craniofacial musculoskeletal complex, such as different muscle recruitment or pinnation patterns, may be responsible.

Animals↗

Aging and reproductive performance in langur monkeys (Presbytis entellus).

Analysis of data on age and reproductive performance in 16 captive female Hanuman langurs (Presbytis entellus) shows that adult females under the age of 6 years and over the age of 19 years had the lowest rates of reproductive success as measured by the production of viable young that survived beyond 30 days of age. With the possible exception of one female, females over the age of 19 years experienced a variety of idiosyncratic reproductive problems but did not experience a true menopause as defined by total cessation of menstrual cycles. There was no support for the hypothesis that langur monkey females have evolved a lengthy postreproductive period.

Aging↗

Kinematics of the cercopithecine foot on arboreal and terrestrial substrates with implications for the interpretation of hominid terrestrial adaptations.

The stereotyped characterizations of quadrupedal foot postures were tested by examining the kinematics of the cercopithecine foot on arboreal and terrestrial supports. Strictly arboreal species were compared with semi-terrestrial species for Cercopithecus, Cercocebus, Lophocebus, and Papio, in semi-natural or experimental settings. Results indicate that the kinematics of the cercopithecine arboreal quadruped differ in degree from stereotypical expectations for an arboreal quadruped. The relatively extended, adducted limb movements of the cercopithecines and the emphasis on the central digit as the functional axis of the foot suggest convergence with terrestrial mammalian cursors, and differ from the platyrrhine or colobine arboreal quadruped. The characteristics of the quadrupedal terrestrial primate foot contrast with the very unique pattern seen in the hominid foot. These contrasts provide a new perspective from which to interpret the hominid adaptation, in which the functional axis has remained fixed between the first and second digits. This pattern differs from virtually all other terrestrial mammals. The influence of bipedalism on this functional pattern is examined.

Animals↗

Facial anatomy of Victoriapithecus and its relevance to the ancestral cranial morphology of Old World monkeys and apes.

Recently discovered craniofacial fossils of the middle Miocene cercopithecoid Victoriapithecus are described. The frontal, zygomatic, maxilla, and premaxilla anatomy differ from the previously proposed colobine-like ancestral cercopithecoid morphotype in several significant respects. This morphotype was based on the assumption that features held in common by subordinate hominoid and cercopithecoid morphotypes (Colobinae and Hylobatidae) are primitive for Old World monkeys. Cranial similarities between Victoriapithecus, which represents the sister-group of both colobine and cercopithecine monkeys, and the shorter-snouted Cercopithecinae (Macaca and Cercopithecus) indicate that the last common ancestor of Old World monkeys possessed the following features: a narrow interorbital septum, moderately long snout, moderately long and anteriorly tapering premaxilla, large procumbent upper central incisors set anterior to and with longer roots than lateral incisors, moderately tall face below the orbits, teardrop-shaped nasal aperture of low height and moderate width, and probably long and narrow nasal bones. The Victoriapithecus cranium is also characterized by features not present in modern cercopithecids. These include a deep malar region of the zygomatic and the presence of a frontal trigon due to the occurrence of temporal lines that merge with supraorbital costae close to the midline of each orbit and converge anterior to bregma. These features are interpreted as primitive retentions from the basal catarrhine condition as indicated by the occurrence of these features among primitive catarrhines (Aegyptopithecus) and Miocene hominoids (Afropithecus).

Animals↗