Phylogeny and patterns of diversification and character evolution within the pelecaniformes: Insight from molecular, morphological, and paleontological data

The Pelecaniformes and the larger waterbird clade that includes them are among the most morphologically and ecologically diverse assemblages of birds. Debate regarding pelecaniform monophyly and interrelationships represents a classic example of discord between morphological and molecular estimates of phylogeny. Robust hypotheses of waterbird relationships are critical to understanding the group's fossil record, temporal pattern of diversification, and the evolution of complex character systems. This dissertation examines patterns of phylogeny and morphological character evolution within the Pelecaniformes and the diverse waterbird assemblage. Chapter Two presents a phylogenetic study of waterbirds utilizing a novel osteological dataset. Pelecaniform monophyly is not recovered, with Phaethontidae recovered as distantly related to all other pelecaniforms, which are supported as a monophyletic Steganopodes. The extinct Plotopteridae are recovered as the sister taxon to Phalacrocoracoidea, and the relationships of other fossil pelecaniforms representing key calibration points are well supported, including Limnofregata (sister taxon to Fregatidae), Prophaethon and Lithoptila (successive sister taxa to Phaethontidae), and ?Borvocarbo stoeffelensis (sister taxon to Phalacrocoracidae). The phylogenetic position of the Plotopteridae implies that wing-propelled diving evolved independently in plotopterids and penguins, representing a remarkable case of convergent evolution. Chapter Three provides a systematic description and analysis of a new fossil species of waterbird representing one of the oldest members of Ciconiiformes (and possibly stem-Threskiornithidae) known, and implies that additional lineages within the waterbird assemblage had diverged by the late Early Eocene. Chapter Four assesses the relationship between skeletal pneumaticity and body mass and foraging ecology in waterbirds. Changes in pneumaticity and body mass are congruent across different estimates of phylogeny, whereas pursuit diving has evolved independently between two and five times. Phylogenetic regressions detected positive relationships between body mass and pneumaticity, and negative relationships between pursuit diving and pneumaticity, whether independent variables are considered in isolation or jointly. Results are consistent across different estimates of topology and branch lengths. Phylogenetically informed `predictive' analyses reveal that several pursuit divers (loons, penguins, cormorants, darters) are significantly apneumatic compared to their relatives. This research sheds new light on waterbird evolution, and outlines a framework for integrating morphological, molecular, and paleontological data in evolutionary studies.