Unraveling the Systematics of Palaeoniscoid Fishes--Lower Actinopterygians in Need of a Complete Phylogenetic Revision

Abstract

Actinopterygian fishes are the most diverse and speciose vertebrates on the planet. Lower actinopterygians, or fishes basal to teleosts, are critical to our understanding of the early evolution of this group, but extant lower actinopterygians are only represented by a few species. A larger diversity is preserved in the fossil record, but these fishes are poorly understood. This dissertation focuses on a subset of the extinct diversity; palaeoniscoid actinopterygians. The term "palaeoniscoid" has been used to refer to a large paraphyletic grouping of fossil fishes ranging from the Devonian to the Cretaceous. Our poor understanding of the diversity and relationships of palaeoniscoids reflects the many taxa of palaeoniscoids that remain to be described and included in phylogenetic analyses, as well as our understanding of morphological characters amongst lower actinopterygians. The main goal of this dissertation is to dismantle the paraphyletic grouping of palaeoniscoid fishes by concentrating on reassessments of morphological characters, descriptions of new taxa, and phylogenetic analyses of a vast number of taxa from the Devonian to the recent using both parsimony and Bayesian methodologies. Chapter One gives a taxonomic review of lower actinopterygians and discusses obstacles that must be overcome in order to form stronger hypotheses of relationships for palaeoniscoids. These obstacles are then addressed in the subsequent chapters. Chapters Two and Three are investigations into morphological characters. Chapter Two examines the preoperculum, a cheek bone considered important in the evolution of actinopterygians. Chapter Three presents problems with how the bones in the snout of lower actinopterygian fishes have been identified and proposes a new identification and nomenclature scheme for the bones of the snout. Chapters Four and Five are descriptions of new taxa from the Carboniferous of Utah and New Brunswick, Canada. Lastly, Chapter 6 presents results of phylogenetic analyses of lower actinopterygians. The data matrix analyzed incorporates the findings from the previous chapters with the addition of new characters, character states, and taxa. This matrix represents the largest analysis to date of lower actinopterygian fishes, and the first time Bayesian methodology is used to investigate the relationships of palaeoniscoid fishes. Results of both methodologies are compared to each other and previously published hypotheses. Most importantly, analysis of this matrix has resulted in the recovery of a monophyletic Paleonisciformes. The results of this chapter suggest that palaeoniscoid actinopterygians represent a natural grouping.