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

• Applicant: Dr. Eli Amson
• Subject Area: Palaeontology ; Systematics and Morphology (Zoology)
• Term: from 2017 to 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 388111938

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.

• DFG Programme: Research Grants
• Co-Investigators: Faysal Bibi, Ph.D.; Professor Dr. Johannes Müller