Division of Mechanical Engineering and Design, London South Bank University , London, UK.
Department of Engineering, King's College London , London, UK.
Proc Biol Sci. 2024 Jan;291(2030):20240774. doi: 10.1098/rspb.2024.0774. Epub 2024 Sep 11.
Sesamoids are variably present skeletal elements found in tendons and ligaments near joints. Variability in sesamoid size, location and presence/absence is hypothesized to enable skeletal innovation, yet sesamoids are often ignored. Three knee sesamoids-the cyamella, medial fabella and lateral fabella-are present in primates, but we know little about how they evolved, if they are skeletal innovations, or why they are largely missing from Hominoidea. Our phylogenetic comparative analyses suggest that sesamoid presence/absence is highly phylogenetically structured and contains phylogenetic signal. Models suggest that it is easy to gain but difficult/impossible to lose knee sesamoids and that the fabellae may have similar developmental/evolutionary pathways that are distinct from the cyamella. Sesamoid presence/absence is uncorrelated to the mode of locomotion, suggesting that sesamoid biomechanical function may require information beyond sesamoid presence, such as size and location. Ancestral state reconstructions were largely uninformative but highlighted how reconstructions using parsimony can differ from those that are phylogenetically informed. Interestingly, there may be two ways to evolve fabellae, with humans evolving fabellae differently from most other primates. We hypothesize that the 're-emergence' of the lateral fabella in humans may be correlated with the evolution of a unique developmental pathway, potentially correlated with the evolution of straight-legged, bipedal locomotion.
籽骨是一种存在于关节附近肌腱和韧带中的骨骼元素，其形态大小、位置和存在与否存在差异，这种差异被认为是骨骼创新的原因，但籽骨往往被忽视。在灵长类动物中存在三种膝关节籽骨——楔骨、内侧籽骨和外侧籽骨，但我们对它们的演化方式、是否属于骨骼创新，以及为什么在人科动物中它们大多缺失知之甚少。我们的系统发育比较分析表明，籽骨的存在与否在系统发育上高度结构化，并且包含系统发育信号。模型表明，获得膝关节籽骨很容易，但失去它们却很困难/不可能，而且外侧籽骨可能具有与楔骨相似的发育/进化途径，但与楔骨不同。籽骨的存在与否与运动方式无关，这表明籽骨的生物力学功能可能需要超出籽骨存在的信息，例如大小和位置。祖先状态重建的结果大多没有提供有用的信息，但突出了使用简约法进行的重建与基于系统发育的重建之间的差异。有趣的是，可能有两种方法可以进化出外侧籽骨，人类的进化方式与大多数其他灵长类动物不同。我们假设，人类外侧籽骨的“重新出现”可能与一种独特的发育途径的演化有关，这种途径可能与直腿、双足运动的演化有关。
