Developmental Morphology of Flippers in Sea Turtles and Penguins

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.