Body Forms in Sharks (Chondrichthyes: Elasmobranchii), and Their Functional, Ecological, and Evolutionary Implications
Date of Award
Master of Science (MS)
Kenshu Shimada, PhD
Windsor Aguirre, PhD
Timothy Sparkes, PhD
Sharks are among the oldest vertebrate lineages in which their success has been attributed to their diversity in body shape and locomotor design. In this study, I investigated the diversity of body forms in extant sharks using landmark-based geometric morphometric analyses on lateral view illustrations of nearly all the known (ca. 470) extant sharks in a published guidebook. I ran three different analyses: the ‘full body,' ‘precaudal body,’ and ‘caudal fin' analyses. My study suggests that there are two basic body forms in sharks. The two major body forms are characterized as a ‘shallow-bodied’ form (Group A) and ‘deep-bodied’ form (Group B). This pattern is also present in the precaudal body analysis, but the caudal fin analysis indicates that all sharks essentially have one basic caudal fin design. My geometric morphometric analyses have significant functional, ecological and evolutionary implications. First, I found that swimming modes in sharks are highly correlated with body forms. For example, Group A sharks are predominantly anguilliform swimmers, whereas Group B sharks are represented by carangiform and thunniform swimmers. Second, the majority of Group A sharks are found to be benthic whereas pelagic forms are relatively common among Group B sharks. Third, based on the known fossil record as well as previously published molecular-based phylogenetic trees, each of the two superorders of sharks, Squalomorphii and Galeomorphii, must have gone through complex evolutionary history where each superorder contains both Group A sharks and Group B sharks, possibly involving parallel evolution from one group to the other or at least one episode of evolutionary reversal. Lastly, the most ancestral shark, the clade that unites Squalomorphii and Galeomorphii, was possibly a benthic form with a Group A body form. My study demonstrates that a use of an identification guidebook can be a powerful method for the field of comparative anatomy.
Sternes, Phillip C., "Body Forms in Sharks (Chondrichthyes: Elasmobranchii), and Their Functional, Ecological, and Evolutionary Implications" (2019). College of Science and Health Theses and Dissertations. 327.