Morphology, ecology and function in elasmobranchs: Comparative analysis of pectoral fins

• Main Author: Sakai, Stacey Akemi
• Format: Text
• Language: English
• Published: DigitalCommons@URI 2011
• Subjects: Morphology|Biology; spiny dogfish; Squalus acanthias
• Online Access: https://digitalcommons.uri.edu/dissertations/AAI1497489

Previous analyses of elasmobranchs have shown that differences in ecology are related to variations in whole body morphologies. Few investigations have analyzed the skeletal and muscular morphologies of the pectoral fins. However, more detailed analyses of the fins are warranted since recent in vivo swimming experiments have revealed that pectoral fins of different species bend to varying degrees during steady swimming and vertical maneuvering, which likely depend on morphological differences. This study aims to determine how pectoral fin morphology is related to ecology and function. Three species of sharks (pelagic Carcharhinus plumbeus, sandbar; benthic Chiloscyllium plagiosum, white-spotted bamboo; epibenthic Squalus acanthias, spiny dogfish) that exploit different habitats were examined. Pectoral fin morphologies were analyzed via dissections and photograph digitizing. Functional differences were assessed through bending experiments. Results indicated that morphological differences are related to ecology and function. Carcharhinus plumbeus appears to be adapted for high-speed cruising with characters that aid in the reduction of drag during locomotion (i.e. relatively stiff distal fin web, long third radial pterygiophores, robust cucullaris, novel subdivision of hypaxialis). In contrast, the pectoral fin morphology of Chiloscyllium plagiosum reflects a benthic lifestyle. The pectoral fins are the most flexible of the study species, which enhances maneuverability through complex environments. Basal pterygiophores are elongate and cylindrical, allowing for a greater range of motion; long first radials and short second and third radials place interradial joints more distally, promoting bending within the middle region of the fin. Fin anatomy of Squalus acanthias appears to be intermediate to the other two species, which supports an epibenthic lifestyle. Fin flexibility is similar to that of the pectoral fins of C. plumbeus, while the presence of a protractor muscle is a character shared with C. plagiosum. Squalus acanthias also possesses plate-like basals and a large area composed only of ceratotrichia, which may represent an alternative approach to stiffening the fin. These relationships among morphology, ecology and function aid in the development of hypotheses regarding lifestyles of extinct or elusive extant sharks. Furthermore, this enhanced understanding of these relationships may also assist in the advancement of biomimetics.