Patterns and processes in the evolution of morphological novelty in the amphibian skull

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Evolutionary transformations are responsible for the origin of the great diversity of animal form, past and present. Evolutionary transformations, such as the transformation from fins to limbs, have captured the attention of naturalists for centuries and have provided the observations needed to establish fundamental theories in evolutionary biology such as natural selection (i.e., decent with modification), the concept of homology, among others. One poorly understood transformation is that which characterizes the origin of the lissamphibian skull form. Lissamphibians (i.e., frogs, salamanders, and caecilians) comprise one half of the dichotomy of living, land-dwelling vertebrates (=tetrapods), the other half of the dichotomy being amniotes (mammals, reptiles and birds). The goal of the proposed research program is to identify and understand evolutionary events that took place in the origin of the distinct lissamphibian skull form. I HYPOTHESIZE that the distinct lissamphibian skull form is the result, at least in part, of shared evolutionary developmental events that took place during the common origin of frogs, salamanders and caecilians. I will address this hypothesis using complementary approaches, synthesizing paleontological data with that from lab-based experiments with living amphibians. I will also conduct fieldwork to retrieve new fossil material to help fill the gaps in the lissamphibian fossil record. The Carboniferous of Nova Scotia represents a critical time period in the evolution of amphibians and has already produced fossils of paramount significance, including the world's oldest amniote and reptile. My fieldwork in Nova Scotia has yielded a plethora of new important discoveries in the last five years, thereby highlighting Canada's natural heritage and adding a facet to Canada's paleontological significance. Study of this new, and currently known, material will reveal new aspects of the pattern of evolutionary events that gave rise to the lissamphibian skull form. Incorporation of data from developmental experiments will shed light on the mechanistic basis, or processes, underlying these evolutionary patterns. The results of this research will revise our understanding of this major tetrapod transformation. Traditionally, lissamphibians have been viewed as representatives of the primitive tetrapod condition, and, as such, are often used to understand the nature and direction of character transformations that seemingly define the well-studied amniote lineage. However, consideration of the fossil record reveals this is not the case, which has led to misinterpretations of evolutionary patterns involving them. Additionally, this research addresses fundamental questions concerning the tempo and mode of the evolution of animal diversity, on multiple hierarchical levels, through the completion of projects spanning Deep- to Real-time.