Zoom link: https://umich.zoom.us/j/9121902198

The remarkable diversity of body plans observed across species reflects millions of years of morphological change. Environmental disturbances and dispersal into new geographic regions can create ecological opportunities hypothesized to trigger rapid bursts of phenotypic diversification. Perspectives on these evolutionary radiations often stem from patterns of diversity apparent in the fossil record or from reconstructing macroevolutionary dynamics using molecular phylogenies of living species. However, these end-member approaches provide incomplete snapshots of biodiversity. Whereas integrating these two complementary, yet distinct natural history records have the potential to yield more accurate macroevolutionary inferences. In this dissertation, I investigate the morphological diversification of Acanthomorpha (spiny- rayed teleosts), a predominately marine fish radiation comprising more than 25% of all extant vertebrates. I also address methodological challenges associated with integrating data of extant and fossil species into a single phylogenetic framework. Specifically, I use a combination of linear morphometrics and phylogenetic comparative methods to examine how past geological events might have altered the phenotypic evolution of three distantly related acanthomorph lineages. First, I use a combined phylogenetic framework of fossil and extant Tetraodontiformes (pufferfishes and allies) to quantify their mode of evolution and test for a shift in evolutionary rate associated with the Paleocene-Eocene Thermal Maximum (PETM). Despite their highly distinctive morphologies, I find that tetraodontiforms are characterized by moderately strong morphological and ecological constraints, and that the PETM had no obvious impact on their morphological diversification. Second, I addressed an outstanding obstacle for studies like that of tetraodontiforms: the lack of a combined phylogenetic framework which subsequently limits the inclusion of fossil data in phenotypic inferences. I use simulations to evaluate alternative methods of incorporating fossil taxa into molecular phylogenies in the absence of a formally inferred tree that includes extinct tips. I demonstrate that methods commonly applied in the literature produce the most misleading inferences, whereas estimating branch length durations for fossil tips using continuous trait data provides the most reliable results. When applying these methods to Carangaria (flatfishes, jack, and allies), I recover evidence of a rapid burst of morphological diversification following the end-Cretaceous mass extinction, a pattern that is obscured when extant only taxa are considered. Third and finally, I investigate whether cross-continental dispersal influences rates of phenotypic evolution in spiny eels (Mastacembelidae). Following their origin in Asia, spiny eels underwent a single dispersal event into Africa. I find that African taxa exhibit elevated rates of morphological diversification relative to their Asian counterparts. Surprisingly, this pattern was not driven by the species flock endemic to Lake Tanganyika, suggesting that the macroevolutionary dynamics characteristic of colonizing insular environments (e.g., islands and freshwater lakes) may also emerge at continental scales. Together, this work demonstrates that multiple factors likely led to the remarkable anatomical diversity of Acanthomorpha. These case studies on individual clades also provide a framework for conducting similar work at the scale of acanthomorphs as a whole. More generally, this dissertation highlights the importance of incorporating fossil information into macroevolutionary inferences and the methodological challenges that remain.