Animal locomotion

There are no modem anatomical studies of flipper development or particularly any
examining limb formation across distantly related taxa converging on similar flipper
morphology. This study compares and contrasts the development of flippers in sea turtle
(Caretta caretta) and penguin (Spheniscus demersus , Eudyptula minor) embryos.
Embryos were fixed, cleared and stained for cartilage anlagen, and prepared as whole
mounts. Skeletal elements forming the flipper and changes in their growth rates were
described across developmental stages. Results suggest skeletal elements contribute
differently to sea turtle and penguin flipper blades and there are significant differences in
bone shape and growth patterns. Greater proportional increases in lengths and areas were
found in sea turtles elements compared to penguins. Sea turtles appear to depend on a
pathway resulting in elongation of distal elements to build a flipper, whereas penguin
limbs undergo flattening and expansion of fewer elements to meet a similar structural
goal.

A robotic ribbon fin with twelve independent fin rays, elastic fin membrane, and a body
of adjustable height was developed for this thesis specifically to test the 1990 theory put forth
by Lighthill and Blake that a multiplicative propulsive enhancement exists for Gymnotiform and
Balisiform swimmers based on the ratio of body and fin heights. Until now, the theory has not
been experimentally tested. Proof of such a momentum enhancement could have a profound effect
on unmanned underwater vehicle design and shed light on the evolutionary advantage to body-fin
ratios found in nature, shown as optimal for momentum enhancement in Lighthill and Blake’s theory.
Thrust tests for various body heights were conducted in a recirculating flow tank at different flow
speeds and fin flapping frequencies. When comparing different body heights at different frequencies
to a ’no-body’ thrust test case at each frequency no momentum enhancement factor was found. Data
in this thesis indicate there is no momentum enhancement factor due to the presence of a body on
top of an undulating fin.

Posthatchling green (Chelonia mydas) and loggerhead (Caretta caretta) turtles overlap ecologically but differ morphologically. This study compared hydrodynamic stability between the two species during swimming to test for functional differences in body shape. Flipper movement paths, four stability measures (yaw, pitch, heave, and sideslip), and the relative positions of the centers of buoyancy and gravity were compared between species. Both centers of buoyancy and gravity lie in the anterior body; their positions relative to one another differed with species, but showed no functional consequences. Neither species demonstrated substantial yaw, sideslip, or pitch. Both experienced upward heave with the flippers' downstroke and downward heave with the upstroke; however phase relationships differed between these limb and body motions. No differences were found between the two species. Despite obvious morphological differences, loggerheads and green turtles were similarly stable during swimming, suggesting that the species use different mechanisms to achieve stability.