Evolution & ecology of Mesozoic birds: a case study of the derived Hesperornithiformes and the use of morphometric data in quantifying avian paleoecology

The discovery of abundant Mesozoic avian fossils, beginning with Archaeopteryx in the 1800’s and increasing dramatically since the 1990’s with the discovery of numerous Chinese fossils, has provided researchers with sufficient quantities of specimens to study the evolution and ecology of ancient birds using phylogenetic and morphometric methods. This study approaches the evolution and ecology of Mesozoic birds from two perspectives – a comprehensive analysis of the Hesperornithiformes, a highly specialized group of diving birds, and a series of morphometric analyses of modern and Mesozoic birds designed to find correlations between ecologic niche partitioning and morphometric trends. ❧ Despite being one of the most taxonomic, geographic, and stratigraphically diverse groups of Mesozoic birds, the Hesperornithiformes have received virtually no comprehensive study since the initial discovery of Hesperornis, Baptornis, and Enaliornis in the late 1800s. This lack of study has resulted in a confusing array of taxa organized into a taxonomic framework beset by errors in description, contradictions, and redundancy. Furthermore, little work has focused on evolutionary relationships among hesperornithiforms, leading to virtually no understanding of their phylogenetic interrelationships. While hesperornithiforms have an extensive fossil record that would be appropriate for morphometric analyses, none have been performed to date, despite the use of numerous morphological features that could be described quantitatively, but instead are treated qualitatively as diagnostic features in the current taxonomic framework. Therefore, the objectives of the first portion of this dissertation are to evaluate and update the current taxonomic framework of hesperornithiform birds (Chapter 1), conduct the first cladistic analysis of the Hesperornithiformes (Chapter 2), identify morphometric trends that may have diagnostic utility (Chapter 3), and integrate these studies to develop a new taxonomic framework informed by the phylogenetic relationships and morphometric patterns identified (Chapter 4). ❧ Among modern birds, morphometric data have been used in a variety of ways in an attempt to correlate ecology with morphology. This study seeks to build on previous work first through the analysis of a new Late Cretaceous ornithuromorph, Hollanda luceria (Chapter 5), and then through a broader analysis of a wide variety of Mesozoic birds (Chapter 6). The goals of these studies are to first test the correlation of ecologic niches with fore- and hind- limb measurements using multivariate statistics, and then to analyze Mesozoic birds in relation to the modern avian morphospace.