KWONG, G.W.*; WYNEKEN, J.; Florida Atlantic University, Boca Raton, FL; Florida Atlantic University, Boca Raton, FL: Comparative and developmental morphology of three marine taxa, Caretta caretta, Spheniscus demersus, and Eudyptula minor – A look at embryonic flipper formation

Evolutionary and developmental origins are intimately connected processes in the natural history of vertebrates and invertebrates. Sea turtles and penguins represent two distantly-related groups that have independently invaded the marine environment. Both groups have highly specialized morphologies differing from their respective ancestors and accompanying their shifts in niche utilization. Interestingly, sea turtles and penguins share similar morphological attributes, such as streamlining of the body and the development of flattened, blade-like flippers. These semi-rigid fore limbs are characterized by flattened and reduced musculoskeletal elements. This morphology serves both sea turtles and penguins in fore limb-driven locomotion. The underlying skeletal arrangements of the limbs differ but the flipper shapes converge on similar form. Examination of fore limb development from limb-bud to near hatching stages allowed us to track the patterns of flipper formation in these two distinct lineages. We compared the fore limb anatomy, identifying the changes in skeletal elements in embryos of the sea turtle Caretta caretta and the penguins Spheniscus demersus and Eudyptula minor across a range of developmental stages in cleared and stained specimens. Here we present a detailed comparative anatomical description of the formation of fore limb elements in these two taxa. We particularly focus on divergence of the distal elements and how their shapes and sizes result in the common flipper form. While grossly similar early in development, the sea turtles diverged from the penguins as the digital plate formed. Elongation of the turtle digital plate led to a less tapered flipper form than we found in the penguins.