The great mammalian evolutionary transitions -Insights from bone micro-anatomy

从陆地祖先状态开始，哺乳动物进化的特点是涉及多种生活方式的重大转变。许多空中的、水生的和地下的适应在哺乳动物进化分支中被多次趋同地获得。由于灭绝的分类群记录了今天没有代表的进化获取，在比较分析中包括来自最近和化石标本的数据是至关重要的。关于与生活方式有关的特征，化石大多保留了骨学特征。此外，骨骼的内部结构特别以功能适应为特征，并且在广泛的分类尺度上具有可比性。因此，我将使用二维（2D）和三维（3D）方法研究生活方式对哺乳动物骨骼微观解剖的影响。虽然与水生适应相关的二维微观解剖学特征（如骨致密性）得到了很好的研究，但那些与空中和地下适应有关的特征要么是肤浅的理解，要么是迄今为止未知的。三维微观解剖特征（如小梁的平均厚度）对生活方式的影响在灵长类动物之外几乎是未知的。因此，将建立一个广泛的哺乳动物微观解剖学数据集，以涵盖它们的主要进化转变。在哺乳动物的非退化状态下，每个标本的肱骨和腰椎将使用高分辨率计算机断层扫描（µCT）进行扫描。定量二维和三维微观解剖参数将提取和研究在系统发育知情框架。首先，将得出关于特别感兴趣的化石的生活方式的结论。其次，探讨了微解剖特征与各主要进化过渡类型之间的关系，并重建了主要枝的祖先状态。最后，整个数据集将用于揭示与重大进化转变相关的模式，例如异常（不是通过自然选择获得的当前角色的特征）的存在以及形态和微观解剖获得的年表。

Starting with a terrestrial ancestral state, mammalian evolution is characterized by major transitions involving diverse lifestyles. Numerous aerial, aquatic, and subterranean adaptations were convergently acquired several times throughout the mammalian clade. As extinct taxa document evolutionary acquisitions that are not represented today, it is crucial to include data from both recent and fossil specimens in comparative analyses. Regarding traits related to lifestyle, fossils mostly preserve osteological features. Furthermore, the inner structure of the skeleton is particularly marked by functional adaptations and comparable over a broad taxonomic scale. I will therefore study the impact of lifestyle on mammalian bone micro-anatomy using two-dimensional (2D) and three-dimensional (3D) approaches. While 2D micro-anatomical features (such as bone compactness) related to aquatic adaptations are well investigated, those that concern aerial and subterranean adaptations are either superficially understood or hitherto unknown. The implications of 3D micro-anatomical features (such as the mean thickness of the trabeculae) on lifestyle are virtually unknown outside primates. A broad micro-anatomical dataset at the scale of mammals will hence be built to encompass their major evolutionary transitions. Consistently found at a non-vestigial state across mammals, the humerus and a lumbar vertebra of each specimen will be scanned using high-resolution computed tomography (µCT). Quantitative 2D and 3D micro-anatomical parameters will be extracted and studied in a phylogenetically informed framework. Firstly, conclusions will be drawn regarding the lifestyle of fossils of particular interest. Secondly, the association between micro-anatomical features and each of the major evolutionary transition types will be addressed, and the ancestral states of major clades will be reconstructed. Finally, the overall dataset will be used to reveal patterns associated with great evolutionary transitions, such as the presence of exaptations (features that were not acquired by natural selection for their current role) and the chronology of morphological and micro-anatomical acquisitions.