UC Riverside

The origin and evolution of pectoral fins remains one of the most important components of vertebrate history. Sharks represent one of the oldest representatives to exhibit paired fins. Yet, there is a paucity of data on the functional and evolutionary aspects of shark pectoral fins. This dissertation aims to bridge those gaps. In Chapter 1, we measured the external pectoral fin morphology of a shark species, the scalloped hammerhead (Sphyrna lewini), that undergoes ecological shifts through ontogeny. We found the pectoral fins changed in shape that are most likely in response the difference in ecological demands that this shark experiences. In Chapter 2, we measured the pectoral fin aspect ratio (AR) of nearly every known (89%) extant shark species and various extinct species. In addition, we coded each species based on their ecology and performed sophisticated evolutionary model fitting analyses. We determined sharks were most likely benthic (i.e., bottom-dwelling) or benthopelagic (i.e., near bottom) in origin and that when sharks shifted to the pelagic (open water) zone of the marine ecosystem, their pectoral fin morphology also changed, clearly demonstrating adaptive evolution. We also realized temperature was a critical driver in shark evolution. In Chapter 3, we used the computational fluid dynamics (CFD) approach to understand the functional aspects of pelagic shark pectoral fins. Our results showed that pelagic shark pectoral fins have different functions compared to benthic sharks. In Chapter 4, we followed up our work in Chapter 1, and compared the scaling trends of shark pectoral fins with various ecologies to determine if any noticeable patterns were present. We realized the scaling of shark pectoral fins is highly complex and that further broader research is warranted.