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ABSTRACT Hapalemur sps . andProlemur simus (bamboo lemurs, collectively) stand out from the relatively homogeneous lemurids because they are bamboo feeders and vertical clingers and leapers. This unique diet presents equally unique challenges, like its verticality, toughness, and toxicity. The bamboo lemurs share the generalized anatomy of the other lemurids, but also display some well‐documented skeletal adaptations, perhaps to overcome the problems presented by their specialization. Soft‐tissue adaptations, however, remain largely unexplored. Explored here are possible soft‐tissue adaptations inHapalemur griseus . We compareH .griseus with other lemurids,Propithecus ,Galago ,Tarsier , and a tree shrew. Based on the available anatomical and physiological data, we hypothesize thatHapalemur andProlemur species will have differences in hindlimb morphology when compared with other lemurids. We predict thatH .griseus will have more hindlimb muscle mass and will amplify muscle mass differences with increased type II muscle fibers. Relative hindlimb muscle mass inH .griseus is less than other prosimians sampled, yet relative sural muscle mass is significantly heavier (P < 0.01) inH .griseus . Results show that the soleus muscle ofH .griseus has a higher amount of type II (fast) fibers in plantarflexors. These findings indicate althoughH .griseus shares some generalized lemurid morphology, its diet of bamboo may have pushed this generalized lemurid to an anatomical extreme. We suspect additional bamboo‐specific adaptations in their anatomy and physiology will be uncovered with further examination into the anatomy of the bamboo lemurs. Anat Rec, 2019. © 2019 Wiley Periodicals, Inc. Anat Rec, 303:295–307, 2020. © 2019 American Association for Anatomy -
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Abstract Objectives It is widely viewed that orangutans lack a
ligamentum teres femoris (LTF) inserting on the femoral head because orangutans lack a distinct fovea capitis. Orangutans employ acrobatic quadrumanous clambering that requires a high level of hip joint mobility, and the absence of an LTF is believed to be an adaptation to increase hip mobility. However, there are conflicting reports in the literature about whether there may be a different LTF configuration in orangutans, perhaps with a ligament inserting on the femoral neck instead. Here we perform a dissection‐based study of orangutan hip joints, assess the soft tissue and hard tissue correlates of the orangutan LTF, and histologically examination the LTF to evaluate whether it is homologous to that found in other hominoids.Materials and methods The hip joints from six orangutans were dissected. In the two orangutans with an LTF passing to the femoral head, the LTF was assessed histologically. Skeletonized femora (n=56) in osteological repositories were examined for evidence of a foveal pit.
Results We observed an LTF in two of the three infant orangutans but not in the sub‐adult or adult specimens. Histological examination of the infant LTF shows a distinct artery coursing through the LTF to the head of the femur. One percent of orangutan femora present with a foveal scar, but no pit, on the femoral head.
Discussion Despite being absent in adults, the LTF is present in at least some orangutans during infancy. We suggest that the LTF maintains a role in blood supply to the femoral head early in life. Because the LTF can limit hip mobility, this may explain why the LTF may be lost as an orangutan ages and gains locomotor independence. These findings enhance our understanding of orangutan hip morphology and underscore the need for future soft tissue investigations.
