Integument-based inferences on the swimming ability and prey hunting strategy of the bigeye thresher shark, Alopias superciliosus (Lamniformes: Alopiidae)
Date of Award
Master of Science (MS)
Windsor Aguirre, PhD
Timothy Sparkes, PhD
Kenshu Shimada, PhD
Alopias is a group of lamniform sharks characterized by a highly elongate caudal fin with three known extant species: A. pelagicus (pelagic thresher shark), A. superciliosus (bigeye thresher shark), and A. vulpinus (common thresher shark). Alopias pelagicus and A. vulpinus are considered fast swimmers and use their caudal fin to hunt for small schooling fish by stunning them, but the feeding behavior has never been directly observed for A. superciliosus. Under the ecomorphological framework, I examined the following four integumentary variables of selected fast swimming (e.g., A. pelagicus, A. vulpinus, and Lamna) and slow swimming (e.g., Mitsukurina and Megachasma) lamniform sharks to determine whether A. superciliosus is a fast swimmer or a slow swimmer: 1) dermis thickness, 2) average interkeel distances of scales, 3) scale density, and 4) scale shape. My integumentary data indicate that A. superciliosus is a slow swimming lamniform, but it likely employs a simple laterally directed tail slap to capture its prey. Its thick dermis layer on the body indicates its extreme body bending capability, perhaps to maximize the strike power of the caudal fin in order to compensate its slow swimming. Overall, my study points to an interpretation that A. superciliosus is an ambush predator, rather than an active prey-pursuing hunter. When my scale density and average interkeel distance data are mapped on to previously published molecular- and morphology-based phylogenetic trees, slow swimming is found to be a plesiomorphic condition in Lamniformes, where the evolution of fast swimming through lamniform phylogeny is more parsimonious in the morphology-based tree than the molecular-based tree. My work is the most extensive comparative study of the morphology and variation of integumentary structures, especially placoid scales, conducted so far for Lamniformes.
Frumkin, Joseph Aaron, "Integument-based inferences on the swimming ability and prey hunting strategy of the bigeye thresher shark, Alopias superciliosus (Lamniformes: Alopiidae)" (2019). College of Science and Health Theses and Dissertations. 334.