Date of Award

8-2014

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Legacy Department

Biological Sciences

Advisor

Dr. Richard W. Blob

Committee Member

Dr. Margaret B. Ptacek

Committee Member

Dr. Timothy E. Higham

Committee Member

Dr. Miriam A. Ashley-Ross

Committee Member

Dr. Michael W. Sears

Abstract

Transitions to novel habitats present different adaptive challenges, producing captivating examples of how functional innovations of the musculoskeletal system influence phenotypic divergence and adaptive radiations. One intriguing example is the transition from aquatic fishes to tetrapods. Recent technological advances and discoveries of critical fossils have catapulted our understanding on how fishes gave rise to terrestrial vertebrates. Considerable attention has been paid to legged locomotion on land, but given that the first tetrapods were aquatic, limbs did not evolve primarily for terrestriality. How, then, is the locomotor function of limbs different from fins? Extant amphibious fishes demonstrate that fins can be used on land, and anatomical analyses of the fish relatives of early stem tetrapods indicate that the appendicular bones of fishes could be quite robust. Consequently, there is a need to evaluate the ability of fins to withstand the physical challenges of terrestrial locomotion in order to shed light on how limbs conferred early stem tetrapods with an upper hand for becoming terrestrial. In the following papers, I have investigated the biomechanical capabilities of different musculoskeletal designs to understand the evolution of terrestrial locomotion in vertebrates. First, I compared the biomechanics of fins and limbs by measuring ground reaction force (GRF) production of mudskipper fishes (Periophthalmus barbarus) crutching and tiger salamanders (Ambystoma tigrinum) walking on level ground, two strategies for accomplishing terrestrial locomotion. Yet, tiger salamanders are already terrestrial. In order to understand how limbs function in a more habitually aquatic tetrapod, I conducted similar GRF analyses on a semi-aquatic newt (Pleurodeles waltl). Once tetrapods moved onto land, a major question is whether locomotion was primarily driven by the forelimbs or the hind limbs. Thus, I evaluated the ability of the forelimbs and hind limbs of A. tigrinum to withstand stresses during terrestrial locomotion. These data provided an opportunity to study whether the bones of different limbs possess different margins of safety against failure. Lastly, I synthesized how extant taxa can be used to model the biology of extinct taxa, advancing our knowledge about how functional innovation of the appendages contributed to one of the greatest revolutions in vertebrate history.

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