Comparative Anatomical Analyses of the Forearm Muscles of Cebus libidinosus (Rylands et al. 2000): Manipulatory Behavior and Tool Use

The present study describes the flexor and extensor muscles in Cebus libidinosus' forearm and compares them with those from humans, chimpanzees and baboons. The data is presented in quantitative anatomical indices for similarity. The capuchin forearm muscles showed important similarities with chimpanzees and humans, particularly those that act on thumb motion and allow certain degree of independence from other hand structures, even though their configuration does not enable a true opposable thumb. The characteristics of Cebus' forearm muscles corroborate the evolutionary convergence towards an adaptive behavior (tool use) between Cebus genus and apes

Visuospatial Integration: Paleoanthropological and Archaeological Perspectives

The visuospatial system integrates inner and outer functional processes, organizing spatial, temporal, and social interactions between the brain, body, and environment. These processes involve sensorimotor networks like the eye–hand circuit, which is especially important to primates, given their reliance on vision and touch as primary sensory modalities and the use of the hands in social and environmental interactions. At the same time, visuospatial cognition is intimately connected with memory, self-awareness, and simulation capacity. In the present article, we review issues associated with investigating visuospatial integration in extinct human groups through the use of anatomical and behavioral data gleaned from the paleontological and archaeological records. In modern humans, paleoneurological analyses have demonstrated noticeable and unique morphological changes in the parietal cortex, a region crucial to visuospatial management. Archaeological data provides information on hand–tool interaction, the spatial behavior of past populations, and their interaction with the environment. Visuospatial integration may represent a critical bridge between extended cognition, self-awareness, and social perception. As such, visuospatial functions are relevant to the hypothesis that human evolution is characterized by changes in brain–body–environment interactions and relations, which enhance integration between internal and external cognitive components through neural plasticity and the development of a specialized embodiment capacity. We therefore advocate the investigation of visuospatial functions in past populations through the paleoneurological study of anatomical elements and archaeological analysis of visuospatial behaviors

Influence of the Task on Hand Preference: Individual Differences among Gorillas (Gorilla gorilla gorilla)

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Food Prehension and Manipulation in <i>Microcebus murinus</i> (Prosimii, Cheirogaleidae)

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Grasping in primates: for feeding, moving and human specificities (Saisir chez les primates: se nourrir, se deplacer et les specificities humanines)

For a long time, humans (genus Homo) were thought to be the only mammalian species capable of dextrous manual grasping. However, grasping is widespread among tetrapods, and among primates, it is associated with a wide range of morphological, dietary and locomotor variation. From an evolutionary perspective, this prompts several questions: is the origin and evolution of grasping in primates derived from requirements associated primarily with feeding or primarily with locomotor behaviour? Are there grasping abilities that are unique to humans? Who made the first tool? The main purpose of this paper is to present a short overview of grasping in primates in order to open a discussion. We show that grasping strategies vary across species, depending on food properties and the substrates used. We also demonstrate that non-human primates can control individual digits, allowing them to use their hands dextrously. Finally, we discuss the challenges that arise in distinguishing anatomical features related to grasping and the debate around the first hominin tool-makers

Hand posture in the grey mouse lemur during arboreal locomotion on narrow branches

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Does the shape of forelimb long bones co-vary with grasping behaviour in strepsirrhine primates?

Fine prehensile activities are often thought to have been associated with the evolution of the human hand. However, there has been no holistic approach establishing the link between the morphology of the forelimb and grasping ability in living primates. The present study investigated the possible relationships between grasping behaviour and the morphology of the forelimb in strepsirrhines in a phylogenetic context. To do so, grasping behaviour during feeding and the shape of the long bones of the forelimb were analysed for 22 species of strepsirrhines. The data obtained show that there is a phylogenetic signal in forelimb morphology in primates in relation to grasping behaviour, but also that there is a marked co-evolution between grasping behaviour and the shape of the humerus and radius. This latter finding suggests a functional association between grasping and forelimb shape, which in turn suggests that bone shape constrains or facilitates behaviour. This result may permit future inferences to be made regarding this behaviour in extinct species and deserves further examination in more detail

Determinants of pull strength in captive grey mouse lemurs

Grasping is important for arboreal species as it allows them to hold on to branches. Although grasping has been studied previously in the context of primate origins and as an indicator of age-induced loss in overall performance, little is known about the proximate determinants of variation in strength. We measured hand pull strength in 62 adult captive individuals of grey mouse lemurs Microcebus murinus of known age. In addition, we measured the body mass and the length of the forearm in each individual. Our results showed that animals with a longer ulna, and animals that weighed more, and had a greater relative body mass had higher pull strength. However, despite the fact that females are bigger than males, differences in pull strength were not significantly different between the two sexes. Although comparative data for other species of vertebrates are scarce, our data suggest that mouse lemurs have relatively high pull strength for their size that may be interpreted as an adaptation to arboreal locomotion

Food acquisition on arboreal substrates by the grey mouse lemur: implication for primate grasping evolution

International audienc