Doctor of Philosophy (PhD)
The biological processes in macroevolutionary transformations, which result in the origin of new species and supraspecific taxa, are not directly observable in organisms with long reproductive generations and need to be extrapolated and reconstructed from physiological, anatomical, and microevolutionary processes. This dissertation reconstructs the anatomical and biomechanical changes that affected the head-neck-shoulder apparatus during the macroevolutionary transformation of a quadrupedal mammal to a bipedal one by studying two model organisms, namely the human and the cat. I hypothesize that the anatomical differences in the head-neck-shoulder apparatus of the two organisms are caused by different force regimes that act on them. I first show that the head-neck-shoulder apparatus of humans suspends the shoulders from the skull. I then demonstrate that the head-neck-shoulder apparatus of cats suspends the head from the thorax. A comparison of the two head-neck-shoulder apparatus shows that the changes necessary to modify a head suspension apparatus to a shoulder suspension apparatus are much more modest than what is usually expected to have taken place during macroevolutionary changes. Thus, it is evident that (1) small structural and configurational modifications can have significant functional and biomechanical consequences; and (2) macroevolutionary transformations of complex systems within complex organisms are amenable to analysis and evolutionary reconstruction.
Document Availability at the Time of Submission
Release the entire work immediately for access worldwide.
Osborn, Michelle L., "The shoulder suspension of bipedal humans and the head suspension of quadrupedal cats : a reconstruction of macroevolutionary changes of complex systems based on nautral experiments, comparative anatomy, and biomechanical analyses of extant organisms" (2013). LSU Doctoral Dissertations. 2485.
Homberger, Dominique G.