Dissertation Research: Origin of the modern avian locomotor system across a neglected evolutionary interval: insight from new methods and new fossils

Yale University, New Haven CT

Investigators

Abstract

Despite the biological novelty of avian flight, little is known about what the most recent common ancestor of birds looked like, nor about how that ancestor flew. Using spectacular new fossil material, sophisticated imaging techniques, and rigorous statistical methods, this research will reconstruct the most likely anatomical and functional attributes of the most recent common ancestor of living birds, bringing us closer to understanding how modern birds and their flying ability came to be. Through museum exhibits, media exposure, and innovative online activities, this project has strong potential to educate both children and adults about evolutionary biology and paleontology. The study will begin with allometric analysis of a comprehensive sampling of fossil taxa. Preliminary results from this analysis (based on >13,000 data points from extant birds) indicate a fundamental allometric division between extant flying and flightless birds. This division, based on the relationship between shoulder joint dimensions and body mass, enables, for the first time, the delineation of well-defined ?flying? and ?flightless? zones for morphology. This novel biomechanical ?test? of powered flying potential can easily be applied to Mesozoic fossils, and preliminary results indicate that the acquisition of a biomechanically favorable shoulder:body mass ratio, enabling powered flight, evolved considerably later in avian evolutionary history than is conventionally assumed. These results set the stage for a novel geometric analysis of Mesozoic stem bird postcrania, which will illustrate when the geometrically modern avian flight apparatus arose, and will shed light on the evolutionary dynamics of this deeply integrated morphological system. Next, the study will focus on the avian crown clade, and will generate the first ever three-dimensional in situ muscle and feather reconstructions of adult extant birds, which will facilitate the robust inference of flight muscle morphology for the most recent ancestor of extant birds. This will form the basis of range-of-motion simulations for the flight apparatus of two pivotal fossil stem birds, validated by data from diverse extant taxa. Together, the project outlined here will rigorously document and mechanically interpret one of the most important functional transitions in vertebrate evolutionary history?the acquisition of modern, powered flying ability in birds.