![]() ![]() More details about the detailed results of the seven dissections are given in the SI and in the forthcoming photographic atlas of bonobos 15. In the present report we provide a first-hand summary of the most important differences between bonobos, common chimpanzees and modern humans and compare these species with other apes and primates in order to assess the broader evolutionary implications of these differences. Thanks also to a collaboration between the Antwerp Zoo and the Applied Veterinary Morphology group of the Department of Veterinary Sciences at the University of Antwerp, arrangements were made for a team of researchers to dissect all seven cadavers (including fetal, infant, adolescent, and adult individuals of both sexes) in circumstances that allowed their anatomy to be compared as the dissections progressed. Few zoos keep bonobos and cadavers are difficult to come by, but thanks to the foresight of researchers at the Antwerp Zoo, which has one of the largest collections of bonobos in captivity, seven bonobo cadavers - six fresh (frozen) and one preserved in formalin – had been preserved. However, until very recently comprehensive data about the soft tissues of panins were only available for common chimpanzees - a previous study of bonobo musculature was incomplete and restricted to a single individual 14. Given the reasonable assumption that the gross morphology of muscles is related to the profound differences in posture, locomotion and dexterity between modern humans and common chimpanzees and bonobos, it is crucial to explore the implications of the pattern of muscle differences that have accumulated in the hominin and panin lineages in the past 8 Ma. The lineages leading to modern humans (hominins) and to common chimps/bonobos (panins) separated c.8 million years ago (Mya), while common chimpanzees and bonobos separated c.2 Mya. genetic evolutionary rates of change among different branches of the primate clade 13. These data were used to generate characters that were used to reconstruct relationships among the taxa sampled 6, 7 and to undertake the first comparison of morphological (muscle) vs. which digits they attach to) and innervation. numbers of muscle bellies), attachments (e.g. The data collected range from the presence or absence of individual muscles to more detailed observations about their morphology (e.g. The initial dissections collected evidence about the muscles of the head and neck (HN) and forelimb (FL) 6, 7 and more recently we have added information about the hindlimb (HL) and trunk 8, 9, 10, 11, 12. Therefore, in the last years we have carried out systematic dissections of cadavers of most extant primate taxa to gather evidence about how soft tissue - in particular striated muscle - gross morphology differs among living primates, with a focus on the great apes. Such genomic evidence provides a comparative framework for understanding the evolutionary time scale of the phenotypic differences among extant apes and between the latter and humans. Since these initial publications better quality data and larger data sets have become available, and recently the publication of an additional 40 complete common chimp/bonobo genomes with a 25-fold sequence coverage has clarified both the timing of the split, and the patterns of subsequent gene exchange, between these two species 5. ![]() In the past decade researchers published the draft sequences of the nuclear genomes of common chimpanzees 1, orangutans 2, gorillas 3 and bonobos 4. We discuss these data in the context of available genomic information and debates on whether the common chimpanzee-bonobo divergence is linked to heterochrony. Puzzlingly, there is an evolutionary mosaicism between each of these species and humans. Moreover, in the hindlimb there are only two muscle absence/presence differences between common chimpanzees and bonobos. Moreover, since the common chimpanzee-bonobo split c.2 Ma there have been no changes in bonobos, so with respect to HN-FL musculature bonobos are the better model for the last common ancestor (LCA) of chimpanzees/bonobos and humans. ![]() Notably, chimpanzees, and in particular bonobos, provide a remarkable case of evolutionary stasis for since the chimpanzee-human split c.8 Ma among >120 head-neck (HN) and forelimb (FL) muscles there were only four minor changes in the chimpanzee clade, and all were reversions to the ancestral condition. We present the first phylogenetic analysis to include musculoskeletal data obtained from a recent dissection of bonobos. Common chimps and bonobos are our closest living relatives but almost nothing is known about bonobo internal anatomy. ![]()
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