I understand that the vertical tails of fish and the horizontal flukes of cetaceans evolved due to the spinal movements of their ancestors but I was just wondering if there has been any investigation into which was the most efficient for swimming (speed, required effort etc...)?
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6$\begingroup$ What kind of swimming? Distance efficiency? Speed efficiency? Acceleration? Manueverability? Cheetahs and kangaroos both have extremely efficient legs, but they're extremely efficient at totally different things. $\endgroup$– ResonatingCommented Jun 21, 2015 at 22:11
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3$\begingroup$ Why would the orientation matter in the first place? The effectiveness will depend on the body shape (other fins, streamlining) and more importantly, cetaceans went back to the oceans, so didn't have as much evolutionary space to develop tuna-like speed and endurance. $\endgroup$– AliceD ♦Commented Jun 22, 2015 at 4:17
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3$\begingroup$ Swimming speed is subject to scaling – larger animals generally swim faster in terms of meters per second. One way to deal with this is to measure speed in body lengths. Scaled like this, speed tends to be proportional to tail beat amplitude and frequency. This seems to hold true across all body plans: wwwextra.inln.cnrs.fr/argentina/publications/… . One way to get at "efficiency" might be to look at the residuals of that relationship to see whether vertical-tailed or horizontal-tailed animals tend be above or below the general relationship. $\endgroup$– OreotrephesCommented Jun 22, 2015 at 15:48
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$\begingroup$ If someone want to dg through the supplementary info for the article I posted above to find those residuals here it is: nature.com.ezproxy.umsl.edu/nphys/journal/v10/n10/extref/… $\endgroup$– OreotrephesCommented Jun 22, 2015 at 15:51
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1 Answer
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For lift-to-drag ratio (so, hydrodynamic efficiency), high aspect ratio semi-lunate tails are most efficient-- leading edge suction is implicated in their ability to produce lift (which provides the thrust for high economy swimmers) while minimizing drag. Convergence of multiple animals (tunas, swordfishes, jacks, pomfrets, whales, ichthyosaurs, etc.) on that tail shape is considered indirect evidence of it's hydrodynamic benefit. So, for speed and energy economy, a tuna like tail, independent of orientation in the water.
NB: other aspects of morphology and physiology are also very important in predicting performance, and a semi-lunate tuna-like tail has often coevolved with these other traits.
More info: http://rspb.royalsocietypublishing.org/content/280/1756/20122071.short http://jeb.biologists.org/content/213/1/89.short https://academic.oup.com/icb/article/24/1/107/104211/Body-Form-Locomotion-and-Foraging-in-Aquatic
