Strachan, Sarah-Jane; (2023) Taxonomic Utility and Phylogenetic Signal of Bone Microstructure within Sauropoda. Doctoral thesis (Ph.D), Taxonomic Utility and Phylogenetic Signal of Bone Microstructure within Sauropoda.

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Abstract

Bone microstructural data can offer insight into the reconstruction of evolutionary histories of extinct taxa, the micro and histological level features within bone often being well preserved. However, to date, few papers have specifically explored the topic in this field, and we are not aware of any studies that have incorporated bone microstructure data formally into phylogenetic analyses for non-avian dinosaurs. To use this data in phylogenies, the presence and strength of a phylogenetic signal within the traits needs to be established. Therefore, the phylogenetic signal in various macro, micro, and histological variables in homologous regions of adult sauropod femora, one of the most widely sampled non-avian dinosaur taxa, was explored. The morphometry of secondary osteons and their canals, osteocytes from woven and parallel-fibered bone and from within secondary osteons, and several indices of robusticity, were tested for phylogenetic signal using Blomberg’s K, Pagel’s λ, Moran's I and Abouheif’s Cmean. Osteocyte aspect ratio, circularity, and minimum diameter from all three bone types showed a strong phylogenetic signal according to Blomberg’s K and were identified as suitable for coding and incorporating into phylogenetic analyses, thus improving our understanding of evolutionary patterns in deep time. In addition, three indices of robusticity, Rd/CT, TI, and RI(CT), showed a moderate phylogenetic signal according to Abouheif’s Cmean. Secondary osteon and canal morphometrics, bone area and cortical thickness did not show a significant phylogenetic signal and were found to be positively correlated with body mass. Although not recommended for inclusion in phylogenetic analyses, these variables may still prove useful for species’ identification and discrimination, particularly when used in a ‘combined approach’ with other data, such as gross morphology and stratigraphy, a recommended approach.

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