<p> This research examines the evolution, phylogenetic distribution, and functional explanations for a peculiar and often overlooked character seen in birds, herein called tracheal and esophageal displacement. Of special interest to this study is examining whether the trait was present in non-avian theropod dinosaurs. This study found that essentially all birds are characterized by a laterally displaced trachea and/or esophagus. The displacement may occur gradually along the neck, or it may happen immediately upon exiting the oropharynx. Displacement of these organs is the result of a heavily modified neck wherein muscles that create mobility restrictions in lizards, alligators, and mammals (e.g., <i>m. episternocleidomastoideus, m. omohyoideus,</i> and <i> m. sternohyoideus</i>) no longer substantially restrict positions in birds. Rather, these muscles are modified, which may assist with making tracheal movements. </p><p> An exceptionally well-preserved fossil theropod, <i>Scipionyx samniticus </i>, proved to be paramount. Its <i>in situ</i> tracheal and esophageal positions and detailed preservation (showing the hallmarks of displacement including rotation, obliquity, a strong angle, and a dorsal position in a caudad region of the neck) demonstrate that at least some theropods were characterized by tracheal and esophageal displacement. Ultimately, the presence of the trait correlates with a highly flexible neck, allowing slack and permitting for the organs to save length as they avoid the long curves of the S-shaped neck.</p>
| Identifer | oai:union.ndltd.org:PROQUEST/oai:pqdtoai.proquest.com:1591019 |
| Date | 14 July 2015 |
| Creators | Klingler, Jeremy Joseph |
| Publisher | Northern Illinois University |
| Source Sets | ProQuest.com |
| Language | English |
| Detected Language | English |
| Type | thesis |
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