Abstract
The origins and early evolution of the bird crown group (Neornithes) are poorly under- stood due to a particularly scarce fossil record. Although recent discoveries have shed much needed light on the diversity of Mesozoic avialans and other feathered dinosaurs, the portion of the phylogeny close to the origin of Neornithes remains sparsely populat- ed by well constrained fossils, and fossil remains bearing directly on the earliest crown group birds remain elusive.Here I investigate the anatomy and phylogenetic relationships of several key fossil spec- imens which bridge this crucial interval in the dinosaur-bird transition. These include the postcranial anatomy of 40 new specimens of the crownward stem bird Ichthyornis, long recognized as one of the closest relatives of crown group birds among non-neorni- thine avialans; and descriptions of Asteriornis maastrichtensis, the oldest well-supported crown bird known, and of Janusavis finalidens, a close relative of Ichthyornis which pre- serves highly informative palatal elements.
The results of this work provide novel evidence on the origin of several morphological features, such as neognathous palate architecture, and clarify the phylogenetic relation- ships of crownward stem birds. These discoveries constitute a substantial addition to our knowledge of the ancestral condition and origins of crown birds, and help close the gap between modern birds and their Mesozoic relatives.
| Date of Award | 24 May 2023 |
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| Original language | English |
| Awarding Institution |
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| Supervisor | Matthew Wills (Supervisor), Daniel Field (Supervisor) & Leslie Turner (Supervisor) |