Browsing by Author "Wilson, Conrad Daniel Mackenzie"

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    An Earliest Carboniferous Actinopterygian Fauna from the Horton Bluff Formation of Nova Scotia
    (2020-01) Wilson, Conrad Daniel Mackenzie; Anderson, Jason S.; Theodor, Jessica M.; Cote, Susanne; Jamniczky, Heather A.; Anderson, Jason S.
    This thesis examines four earliest Carboniferous (Tournaisian) actinopterygian specimens from the Horton Bluff Formation of Nova Scotia. I used traditional and μCT descriptive techniques in order to better understand actinopterygian evolution and the transition between Devonian and Carboniferous vertebrate faunas. NSM 017.GF.017.001 was investigated using microscopy and latex peel techniques and represents the oldest occurrence of a deep-bodied actinopterygian. NSM 017.GF.017.007 and NSM 017.GF.017.004 were investigated using microscopy and μCT. Neither specimen can be assigned to genus or species, however, each can be compared to a broader group. NSM 017.GF.017.007 is most similar to Devonian taxa, whereas NSM 017.GF.017.004 is most similar to actinopterygians deeply nested in a broad post-Devonian radiation. NSM 017.GF.017.005 was examined using μCT and was incorporated into a phylogenetic analysis. In this specimen, the plesiomorphic anatomy of the dermal shoulder girdle, pectoral fin, and opercular-gular series are contrasted with the derived anatomy of the hyoid arch. In the phylogenetic analysis, it is recovered as a late-diverging member of a grade of otherwise Devonian actinopterygians. The presence of NSM 017.GF.017.001 and NSM 017.GF.017.004 suggests that derived actinopterygians faunas were established by the Tournaisian; whereas the presence of NSM 017.GF.017.007 and NSM 017.GF.017.005 suggests that Hangenberg extinction survivorship was inclusive of early-diverging actinopterygians. NSM 017.GF.017.001 and NSM 017.GF.017.005 also evince actinopterygian body plan exploration, perhaps related to resource acquisition, in the Tournaisian and revise previous models of post-Hangenberg actinopterygian differentiation. More broadly, the disparity of this fauna weakens interpretations of a homogeneous earliest Tournaisian caused by mass extinction and suggest that faunal turnover was more gradual than expected, at least in Actinopterygii.