[CT Birds] Dissertation Defense - Daniel Field - Avian Flight

Amy Hopkins hopkinsus at cs.com
Tue May 3 17:07:36 EDT 2016

Dissertation Defense 

Open to the public
Monday, May 9, 2016
2:00 PM
KGL 123 (room 123 of Yale's Geology Building (right next to the Peabody)
Daniel Field – “Macroevolutionary patterns in total-clade Avialae: the complex evolution of avian biogeography, and the origin of avian flight”
Committee:  Jacques Gauthier (advisor), Derek Briggs, Anjan Bhullar, Rick Prum (EEB)

Birds are among the most diverse and ubiquitously distributed tetrapod clades; they inhabit a myriad of different environments, and exhibit incredible disparity in their forms and lifestyles. Unraveling how, when, and why this diversity has arisen demands an appeal to the fossil record of crown birds (Neornithes), as fossils provide us with the only direct evidence of neornithine evolutionary history. Additionally, understanding the origins of the features that make birds unique—such as feather-assisted flight—forces us to look outside of Neornithes to the avian stem lineage, where the nature, timing, and order of character transformations are only accessible through fossils. Here, macroevolutionary patterns in Avialae are investigated first in terms of the radiation and biogeography of early crown birds, and second in terms of one of the most significant evolutionary transitions that preceded and enabled that radiation: the origin of powered flight.

The value of fossils in crown group macroevolutionary analyses is explored by investigating the affinities ofForo panarium, an enigmatic Eocene bird from western North America. Comprehensive phylogenetic analyses strongly supportF. panarium as a total-clade turaco, a clade whose crown group is restricted to sub-Saharan Africa.F. panarium provides a striking example of the dynamic nature of avian biogeography, and a large-scale historical biogeographic analysis of extant and fossil crown birds reveals the critical importance of fossils in ancestral area reconstructions.

Next, methods of body mass estimation for fossil birds were revised with an unprecedentedly comprehensive allometric dataset, yielding equations that improve the precision of mass estimates and statistical prediction intervals. This dataset reveals the ratio between glenoid diameter and body mass as a previously overlooked osteological correlate of powered flying ability in crown birds. This ratio can be readily evaluated in fossils from the avian crown and its proximal stem, and reveals marked differences in the aerial capacity of crownward avialans such as Ichthyornis, and comparatively stemward taxa such asArchaeopteryx, corroborating recent evidence from feather and skeletal morphology. These data suggest that modern powered flight arose later in avian evolutionary history than previously assumed, and clarify the pattern by which flight—one of the most characteristic features of Neornithes—evolved along the avian stem. 

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