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PubMed2004

Form and function of the oblique cord (chorda obliqua) in anthropoid primates.

The oblique cord of the forearm in humans is a ligament connecting the anterolateral aspect of the ulna proximally to the posteromedial aspect of the radius distally, inserting just below the radial tuberosity. Its functional significance is uncertain, but it has been proposed that the ligament limits supination of the forearm or aids in resisting buckling failure in the curved radius. These functional explanations are unsatisfactory for bipedal humans who do not use their forelimbs in weight support. Furthermore, there are no evolutionary explanations for its presence in humans. The purpose of this study was to investigate the distribution and form of the oblique cord in non-human primates and to explore its possible functional significance and evolutionary origin in humans. Soft tissue dissections of anthropoid primates revealed the presence of an oblique cord in New and Old World monkeys and Asian apes. It was absent in all atelines. Passive manipulation of the two forearm bones in all specimens revealed that the ligament becomes most taut in pronation contrary to the proposed human condition. Isolated radii show that the oblique cord's radial insertion lacks a clear relationship with bone curvature, thus providing little support for the hypothesis of preventing buckling failure. The oblique cord's involvement in reducing bending strain in the curved radius is also unlikely. It is suggested here that the ligament may have a role in maintaining elbow stability in quadrupedal primates. Therefore, the function of the oblique cord in anthropoid primates suggests that its presence in modern humans may be a morphological and functional remnant from a quadrupedal ancestry.

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PubMed2004

Accelerated evolution of the electron transport chain in anthropoid primates.

Mitochondria are both the power plant of the cell and a central integrator of signals that govern the lifespan, replication and death of the cell. Perhaps as a consequence, genes that encode components of the mitochondrial electron transport chain (ETC) are generally conserved. Therefore, it is surprising that many of these genes in anthropoid primates (New World monkeys, Old World monkeys and apes, including humans) have been major targets of darwinian positive selection. Sequence comparisons have provided evidence that marked increases of non-synonymous substitution rates occurred in anthropoid ETC genes that encode subunits of Complex III and IV, and the electron carrier molecule cytochrome c (CYC). Two important questions are: (i) how has evolution altered ETC function? and; (ii) how might functional changes in the ETC be linked to evolution of an expanded neocortical brain?

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PubMed1997

Dentition of Proteopithecus sylviae, an archaic anthropoid from the Fayum, Egypt.

Proteopithecus sylviae is an archaic anthropoid from the late Eocene quarry L-41, Fayum Province, Egypt. The dentition of Proteopithecus is very primitive and does not closely resemble that of other, better known, primates from the Fayum (e.g., parapithecids and propliopithecids). The dental morphology, much of which is described herein, shows a platyrrhine-like level of organization, suggesting that P. sylviae may occupy a position near the base of the modern anthropoid radiation.

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PubMed1998

Parenting and survival in anthropoid primates: caretakers live longer.

Most anthropoid primates are slow to develop, their offspring are mostly single births, and the interbirth intervals are long. To maintain a stable population, parents must live long enough to sustain the serial production of a sufficient number of young to replace themselves while allowing for the death of offspring before they can reproduce. However, in many species there is a large differential between the sexes in the care provided to offspring. Therefore, we hypothesize that in slowly developing species with single births, the sex that bears the greater burden in the care of offspring will tend to survive longer. Males are incapable of gestating infants and lactating, but in several species fathers carry their offspring for long periods. We predict that females tend to live longer than males in the species where the mother does most or all of the care of offspring, that there is no difference in survival between the sexes in species in which both parents participate about equally in infant care, and that in the species where the father does a greater amount of care than the mother, males tend to live longer. The hypothesis is supported by survival data for males and females in anthropoid primate species.

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PubMed1975

Incisor size and diet in anthropoids with special reference to Cercopithecidae.

In 57 species of anthropoids relative size of incisors in highly correlated with diet. Anthropoids that feed primarily on large food objects (large fruits) have larger incisors than those that feed on smaller food objects (berries or leaves). This difference reflects a need for more extensive incisal preparation of larger food objects before mastication. Extensive incisal preparation causes increased tooth wear, therefore, enlarged incisors are probably an adaptive response to increase their wear potential.

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PubMed1998

A comparison of encephalization between odontocete cetaceans and anthropoid primates.

There have been very few studies of brain size and encephalization in cetaceans and essentially none that have made direct quantitative comparisons of cetaceans and another mammalian group using large normative samples. In the present study two different measures of encephalization were calculated and used to rank and compare 21 odontocete species and 60 anthropoid primate species. Comparisons were made both within and between the two groups. Results show that the encephalization level of Homo sapiens is still extraordinary relative to that of nonhuman species. Nevertheless, a subset of delphinid odontocetes are significantly more highly encephalized than the most highly encephalized anthropoid primates and narrow the gap in encephalization between humans and nonhumans substantially. These findings may have implications for comparative models of the relative importance of brain size versus brain organization for the evolution of intelligence.

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PubMed2000

Relative volume of the cerebellum in dolphins and comparison with anthropoid primates.

According to the 'developmental constraint hypothesis' of comparative mammalian neuroanatomy, brain growth follows predictable allometric trends. Therefore, brain structures should scale to the entire brain in the same way across mammals. Evidence for a departure from this pattern for cerebellum volume has recently been reported among the anthropoid primates. One of the mammalian groups that has been neglected in tests of the 'developmental constraint hypothesis' is the cetaceans (dolphins, whales, and porpoises). Because many cetaceans possess relative brain sizes in the range of primates comparative tests of the 'developmental constraint hypothesis' across these two groups could help to delineate the parameters of this hypothesis. In this paper, we compare relative cerebellum volumes in two cetacean species, the bottlenose dolphin (Tursiops truncatus) and the common dolphin (Delphinus delphis), with published data from anthropoid primates. We found that relative cerebellum size is significantly greater in the two dolphin species than in any of the primates, including humans. These results suggest that there is possibly expansion of brain structures independent of strictly allometric processes.

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PubMed1989

Relationships between cerebral indices for 'extra' cortical parts and ecological categories in anthropoids.

The relationships between cerebral indices for 'extra' cortical parts associated with advanced functions [Jerison's 'extra' neurons (Nc), Hofman's 'extra' cortical volume (Ve)] and ecology and social structure were examined for a total of 86 species of anthropoids (28 species of New World monkeys, 48 species of Old World monkeys and 10 species of apes). The species were divided into a total of 39 'congeneric groups' of species which share common ecology and social structure (in most cases, congeneric groups are synonymous with genera). Both Nc and Ve were significantly larger for polygynous congeneric groups than for monogynous congeneric groups in the case of New World monkeys. In the case of Old World monkeys, both Nc and Ve were significantly larger for terrestrial congeneric groups than for arboreal congeneric groups. In the case of apes, although complete analyses could not be performed because of the limited size of the sample for which data were available, both Nc and Ve appeared to be larger for polygynous/terrestrial apes than for monogynous/arboreal apes. These results suggest that the expansion of the cerebral cortex in anthropoids may be associated with terrestriality and polygyny.

Animals↗
PubMed1987

Relative size of the anterior thalamic nuclei differentiates anthropoids by social system.

Anthropoid primates differ in the sizes of their limbic nuclei. Morphometric analysis of the anterior principal thalamic nucleus and the medial mamillary nuclei reveal that both regions increase in size as a function of brain weight. However, after controlling for the size of the brain, anthropoids classified as having single-male societies have more anterior principal thalamic neurons than do primates that are classified as multi-male. The relative sizes of the mamillary nuclei do not show this clustering. The differences in the size of the anterior nucleus are hypothesized to be specific for this nucleus and not the result of a general limbic or of heterochronic changes.

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PubMed1975

Origins of anthropoid intelligence.

The development of the extrastriate visual system relative to the striate system was estimated indirectly by measuring the volumes of the lateral posteriorpulvinar complex and lateral geniculate nucleus in six varieties of mammals selected on the basis of their propinquity with Anthropoidea [oppossums, hedgehogs, rats, squirrels, tree shrews and bushbabies]. The same animals were tested on two related behavioral tasks [spatial and visual reversal learning] whose successful achievement requires a simple sort of abstraction. The results show that the ability to learn visual reversal, but not spatial reversal, corresponds closely to the relative degree of development of the extrastriate system. Since the variation in both these behavioral and morphological characteristics also parallels the phylogenetic dimension, the recency of common ancestry to anthropoids, the evolutionary origin of the anthropoid capacity for visual abstraction is suggested.

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PubMed1975

[Further studies of the cytoarchitectonic division in the dorsal surface of the lst temporal gyrus of a linguistic genius and 2 anthropoids].

1. As an addition to already published studies in this journal (BEHEIM 1974) about the cytoarchitectonic divisions in six left human dorsal surfaces, the left and the right dorsal surface of a linguistic genius and of two anthropoids were examined; a second human right dorsal surface was used for a comparison. 2. In all these cases it was possible to confirm the presented in the first article dividing characteristics of the described partitions of the cortex in spite of considerable cytoarchitectonic differences between individuals, as well as, between left and right dorsal surfaces. 3. The linguistic genius (El 9) showed on the left side a striking development of the 2d transverse gyrus by the repetition of two fields and threefold increase of the most interior field of the medial segment with the smallest nerve cells of the tr 2. 4. On the right side El 9 revealed, besides a considerable narrowing of the caudal part of the lst transverse gyrus in the 2nd transverse gyrus, only division into two parts of the medial segment of the gyrus; the most interior field was missing. The caudal field of the tr 2 and regio t par tr were large in comparison with the left side. A similar picture was presented by the right dorsal surface in the case of the highly musical scientist (El 2) in whom the left tr 1 was especially extensive. In both right dorsal surfaces the nerve cells of the tr 1, especially in markedly narrowed caudal part, were very small; the nerve cells of the tr 2 - exclusive tr 2 c - were smaller than on the left side - as much as it was possible to judge without comparative microphotographs; the nerve cells of the tr 2 c appeared to correspond to that on the left side. In regio t par tr the nerve cells, practically of "normal" size, were so severely damaged that it could not be topographically differentiated. 5. In both anthropoids, the topography of the dorsal surfaces was similar to that of the man; in both left sides area tr 1 c could not be subdivided; on the right side the differentiation between the subareae of tr 1 i and tr 1 c was even not possible. In tr 2 on both sides it was possible to divide in two the middle part of the gyrus similarly as in examined human right side; in addition there was a conspicuous extension of the lateral and caudal area of the tr 2. 6. The literature concerning the left-right differences in the dorsal surfaces and about the sensory primary auditory cortex is quoted and discussed.

Adolescent↗
PubMed1997

Volumetric comparisons in the cerebellar complex of anthropoids, with special reference to locomotor types.

Seven measurements in the cerebellar complex were completed on 45 individuals, including 26 species of anthropoids from Stephan's collection. These included 12 species of New World monkeys, 10 species of Old World monkeys, and Hylobates, Gorilla, Pan, and humans. The measurements were the volume of medial (fastigial) (CM), interpositus (globose and emboliform) (CI), and lateral (dentate) (CL) cerebellar nuclei, ventral pons (VPo), inferior olivary principal (OLIPr), and accessory (OLIAc) nuclei and vestibular nuclear complex (VES). The relative size of each nucleus was expressed in size indices based upon the allometric line obtained by the reduced major axis analysis. The indices of three cerebellar nuclei reflect the relative size of three longitudinal zones of the cerebellum. The cerebellar hemisphere-lateralis zone is represented by the CL indices, the vermis-medialis zone by the CM indices, and the pars intermedius-interpositus zone by the CI indices. The results show that the VPo and OLIPr indices are closely related to the CL indices. This lateral zone group of nuclei is the most progressively developed in humans, whereas the CM, CI, OLIAc, and VES are independent of the developmental trend manifest by the lateral zone group of nuclei. The indices are discussed in relation to the predominant locomotor pattern exhibited by a species. The size indices of arboreal quadrupeds show a development of all nuclei in the cerebellar complex. This is interpreted as indicating that arboreal monkeys live in complicated, discontinuous, three-dimensional space and need exceptional cerebellar capacity for each pattern of locomotion and positional behavior. Progressive development of the lateral zone group of nuclei only compared to other nuclei was recognizable in humans. This development is considered to be related not to bipedalism, but to versatile and coordinated finger movement, resulting after bipedalism was established. This cerebellar reorganization is also a prerequisite (Leiner et al. [1993] TINS 16: 444-447) for the evolution of human language. The differences between size indices of the nuclei of Macaca (= pronograde primate) and Ateles (= antipronograde one) are compared in relation to their vertical climbing kinesiological data.

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PubMed1998

Femoral anatomy of Aegyptopithecus zeuxis, an early oligocene anthropoid.

Three partial femora from Quarries I and M of the early Oligocene Jebel Qatrani Formation in the Fayum of Egypt are attributed to Aegyptopithecus zeuxis on the basis of their appropriate size and anthropoid morphology. Compared with extant catarrhines, Aegyptopithecus is unusual in having a distinct gluteal tuberosity (third trochanter) and a relatively deep distal femoral articulation. In the estimated neck angle, Aegyptopithecus resembles arboreal quadrupeds rather than either leaping or suspensory primates. It seems likely that the femur of this species was relatively robust and short for its body mass. In aspects of its femoral anatomy, Aegyptopithecus is quite different from the parapithecid Apidium and more similar to Catopithecus from late Eocene deposits of the Fayum, and also to small hominoids from the Miocene of East Africa.

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PubMed1999

Constraints on masticatory system evolution in anthropoid primates.

It is well established that some observed patterns of force production in the primate masticatory system match those predicted by a simplified lever model. This model is also commonly invoked in adaptive explanations of craniodental diversity. However, systematic studies of the predictive power of this model are missing, leaving open the possibility that factors not traditionally included in the model alter the function and evolution of the masticatory system. One such factor was proposed for mammals generally by Greaves ([1978] J. Zool. (Lond.) 184:271-285), who argued that the temporomandibular joint (TMJ) was poorly suited to being pulled apart. In this constrained lever model, the avoidance of joint distraction leads to limitations on masticatory system form and function. The goal of the present study was to quantify masticatory system diversity in anthropoid primates for comparison with these predictions. Results indicate that all sampled taxa exhibit a form that is consistent with selection against regular distraction of the TMJ. Also apparent from observed patterns of scaling is a regular interaction among a limited set of cranial and dental dimensions, in accordance with the constrained model. However, the data indicate that specific positional relationships among the muscles, joints, and teeth differ from those predicted by Greaves (1978). The pattern of deviation suggests that selection has favored a conservative masticatory system configuration that safeguards the TMJ from distraction during the dynamic processing of irregular foods. The resulting buffered model leads to alternative hypotheses regarding the response of the masticatory system to dietary selection pressures. It may, therefore, improve our understanding of the adaptive significance of primate craniofacial form.

Animals↗
PubMed2004

Use of spatial, visual, and olfactory information during foraging in wild nocturnal and diurnal anthropoids: A field experiment comparing Aotus, Callicebus, and Saguinus.

Early in their evolution, the ancestors of anthropoid primates radiated from a nocturnal to a diurnal niche. Foraging during the night differs from foraging during the day in terms of the availability of light and color cues, and in the movement of odor molecules through the canopy. In this study, we compared the ability of nocturnal and diurnal New World monkeys to use perceptual cues (i.e., the sight or smell of food) and spatial information (place predictability) in within-patch foraging decisions. An experimental field study was conducted on wild groups of night monkeys (Aotus nigriceps), tamarins (Saguinus imperator imperator and S. fuscicollis weddelli), and titi monkeys (Callicebus cupreus) at the Zoobotanical Park/UFAC, Rio Branco, Brazil. Our research design included the construction of feeding stations located in the home range of the study groups. Each feeding station consisted of eight visually identical feeding platforms located in a circular arrangement. In all test settings, two platforms at each feeding station contained a food reward (banana), and the remaining six platforms contained a sham reward (yellow plastic or inaccessible banana). In the night-monkey experiments, each feeding platform was illuminated by a 40-W red bulb to aid the researcher in observing their behavior. When the location of reward sites was predictable over time, individuals in all four species successfully relocated food rewards based solely on spatial information. Each species was also successful in using visual information to distinguish real from sham food rewards. However, only night monkeys and one group of emperor tamarins used olfactory information alone to locate food rewards. Overall, the species' performances did not clearly differentiate Aotus from diurnal New World primates in these experiments.

Animals↗
PubMed1978

Morphoclinal variation in the anthropoid shoulder.

A morphocline in the organization of the shoulder joint is demonstrated among anthropoid primates. This metrical test supports the view that hominoid distinctions are monophyletic in origin. The primates that are behaviorally and functionally convergent on hominoids are only partially convergent or are not convergent in shoulder morphology.

Animals↗
PubMed1978

A functional analysis of the primate masticatory system and the origin of the anthropoid post-orbital septum.

Study of the dry weights of primate and non-promate masticatory musculature reveals a significant relationship between the Anterior Temporalis/Masseter ratio and the relative development of the anterior dentition. Available dietary information demonstrates that species emphasizing incisal preparation of food have a high AT/M index; species emphasizing molar occlusion have a low AT/M index. Utilizing this information, a model is presented of the origin of the anthropoid post-orbital septum. Frugivory or extensive incisal preparation of food is causally related to the development of the post-orbital septum, because diet can then create selection pressures for an increasingly tendinous and enlarging anterior segment of the temporalis muscle which requires additional bony areas of orgin in the anterior temporal fossa. Cenozoic climatic oscillations leading to increasing seasonality may have been the triggering element in this model, because seasonality creates periods in which the availability of fruit is relatively predictable.

Animals↗
PubMed1982

The humerus of Aegyptopithecus zeuxis: a primitive anthropoid.

Two complete humeri of Aegyptopithecus zeuxis have been recovered from Oligocene deposits in the Fayum Province of Egypt. These new specimens support previous interpretations of the locomotor adaptations of this species and indicate that A. zeuxis was a robust, slowly moving arboreal quadruped. While the previously described distal articular region of the humerus is virtually identical with the same region in many extant ceboids and the Miocene hominoid Pliopithecus vindobonensis, the more proximal parts of the humerus show many primitive "prosimianlike" features not found the limbs of extant anthropoids. The primitive features include the absence of a distinct deltoid plane, a broad shallow bicipital groove, a large brachialis flange, and an entepicondylar foramen. In most features, the humerus of Aegyptopithecus zeuxis is more primitive than the hypothetical last common ancestor of extant cercopithecoids and hominoids based on neontological comparisons. This supports other lines of evidence indicating that the hominoids from the Egyptian Oligocene are morphologically ancestral to both Old World monkeys and apes.

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