Abstract
Hammerhead sharks are characterized by a conspicuous lateral expansion of the head forming a structure known as a cephalofoil. Two theories regarding the function of this structure suggest that it may increase maneuverability as well as produce dynamic lift similar to a cambered airplane wing. Here we report on a family-wide computational fluid dynamics analysis of all eight hammerhead shark species and three sharks with typical head shape. Models cast of the heads of fresh and museum specimens of hammerhead and typical sharks were used to produce pressure surface maps and lift and drag polar diagrams at various angles of attack. These analyses suggested that the cephalofoil (1) provides greater maneuverability that may be important in prey capture efficacy, (2) does not provide significant dynamic lift when held parallel to flow, (3) is characterized by greater drag than typical sharks across all attack angles, and (4) was found to result in a 10-x increase in energetic cost over typical shark head morphologies.
Highlights
Hammerhead sharks are characterized by a conspicuous lateral expansion of the head forming a structure known as a cephalofoil
Hammerhead cranial morphologies are united by strong dorsoventral flattening and lateral expansion resulting in an anterior cephalofoil or “head-wing” with the eyes situated distally at each lateral end; substantial morphological variation exists across the clade
Mean dorsal pressures were higher than ventral pressures in six of the eight species (S. lewini, tudes, media, tiburo and corona, and E. blochii) and, in most cases, dorsal pressures were much higher than ventral
Summary
Hammerhead sharks are characterized by a conspicuous lateral expansion of the head forming a structure known as a cephalofoil. Models cast of the heads of fresh and museum specimens of hammerhead and typical sharks were used to produce pressure surface maps and lift and drag polar diagrams at various angles of attack. These analyses suggested that the cephalofoil (1) provides greater maneuverability that may be important in prey capture efficacy, (2) does not provide significant dynamic lift when held parallel to flow, (3) is characterized by greater drag than typical sharks across all attack angles, and (4) was found to result in a 10-x increase in energetic cost over typical shark head morphologies. CFD is cost-effective, its models are easy to manipulate, and it enables flow visualization at levels of resolution otherwise impossible to obtain in a conventional laboratory setting
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