Patterns of torso morphology in extant quadrupedal amniotes and their paleontological applications
Date of Award
Master of Science (MS)
Timothy Sparkes, PhD
Windsor Aguirre, PhD
Kenshu Shimada, PhD
The relationship between form and function is an overarching theme in the field of biology. Specifically, body size and shape are important factors when considering the biology of an organism. This study examined the torso morphology of a diverse set of 124 extant terrestrial and semi-aquatic amniote taxa using a novel approach to construct approximated torso shape groupings. My study shows the presence of 10 distinct torso shapes within the examined amniotes, and these torso shape groupings were used to evaluate hypotheses associated with diet and limb bone length as well as explore potential evolutionary patterns. Herbivores had a more voluminous torso and were most commonly found to exhibit a torso shape with a wider girth. Also, a statistically significant relationship of certain torso shapes with limb bone lengths was found. These results can be useful for reconstructing extinct taxa. If a relatively complete skeleton is discovered that includes a well-preserved humerus or femur and a torso length is able to be determined, then a torso shape can be approximated using the results of this study. Phylogenetic character mapping identified potential homologous torso shapes in lagomorphs and rodents as well as in artiodactyls and perissodactyls given shared ancestry in these groups. Additionally, potential homoplasious shapes in reptiles and some semi-aquatic mammals were found. This study explored factors that might affect the shape of the amniote torso and provides additional evidence to support that herbivores have large and voluminous torsos to accommodate a gastrointestinal tract needed to digest plant material. Other factors that might influence torso shape include cursoriality, mode of thermoregulation, habitat, life-history, and behavioral or morphological adaptations in response to large scale environmental changes. This study represents a relatively simple and novel approach to investigating a seemingly understudied aspect of the amniote body plan, the shape of the torso.
Walsh, Myles M.A., "Patterns of torso morphology in extant quadrupedal amniotes and their paleontological applications" (2021). College of Science and Health Theses and Dissertations. 454.