Morphological and biomechanical predictions of cranial kinesis in reptile evolution

Abstract

Feeding is a complex behavior that all tetrapods engage in on a regular basis to procure energy and survive. The reptilian feeding apparatus includes many types of feeding behaviors including multiple methods of engaging cranial kinesis, the ability to move one portion of the skull in relation to another portion of the skull. Understanding the underlying mechanisms of cranial kinesis enabled feeding mechanism is integral to understanding avian feeding behaviors, strategies, and ecology. Chapter 1 introduces how the feeding apparatus of reptiles is modified during the evolution of birds from dinosaur and reptile relatives. During this introductory chapter I lay the foundation for our knowledge of avian feeding and its evolution and describe the musculoskeletal environment of the avian feeding apparatus, which becomes the main focus of the rest of this project. Chapter 2 explores the diversity of jaw muscle resultants across a sample of birds, dinosaurs and other reptiles using ternary plots. Jaw musculature orientations are altered across ontogeny, behavior, and evolution. I use ternary plots to investigate the diversity of jaw muscle orientations across the ontogeny and feeding behaviors of alligators and through evolution in the dinosaur to bird lineage. Additionally, I use ternary plots to show how diverse organisms use different muscles to produce high bite forces. Chapter 3 introduces and demonstrates the use of postural modeling to investigate the feeding apparatus at a specific instant of a feeding behavior. I investigate the kinetic capability of 3 taxa using this method. I use my postural modeling method to validate postural models of known behaviors in extant taxa first. I then evaluate the kinetic capabilities of an extinct animal, Tyrannosaurus rex. Finally, Chapter 4 investigates the diversity of the feeding apparatus across parrots, a lineage of morphologically comparable birds with distinctive ecological roles. The biomechanical requirements of similar functional morphology used for diverse feeding behaviors are analyzed here. I use statistical and finite element analyses to describe the biomechanical environment of the feeding apparatus in parrots. I analyze stress and strain dissipation as well as geometric properties of bone mechanics that enable parrots to engage in cranial kinesis. I use a phylogenetic tree informed by molecular phylogenies to plot and compare ancestral reconstructions of characters of the feeding apparatus in parrots. My findings using these methods describe the diversity of the musculoskeletal systems of diverse parrots. The data gathered from the studies described here form the foundation of a better understanding of the biomechanics of the avian feeding apparatus. The findings described here will be used in future studies to describe the underlying mechanisms that govern diverse feeding behaviors.