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Abstract

The recreation of behavior in extinct fossil taxa is a difficult task, and many studies have attempted to analyze the feeding mechanics of early tetrapods on the basis of fragmentary elements or a priori assumptions of terrestrial selective pressures. The transitional fossil, Tiktaalik roseae, preserves exquisite details of many elements of the feeding apparatus of a derived, tetrapodomorph fish that existed right before the fin-to-limb transition. Here I present an in-depth study of the feeding mechanics of this important fossil on the basis of detailed internal anatomy, modern analogs, and cranial linkage reconstructions to attempt an all-data approach to reconstruct feeding behavior in this important taxon: Using micro computed tomography (µCT) to visualize joint surfaces, deformation patterns, and internal feeding anatomy of the Tiktaalik, the first section of this work demonstrates the transitional nature of elpistostegid feeding anatomy. The cranium of Tiktaalik is shown to be platyrostral and consolidated in similar ways to more derived tetrapodomorphs, but the modified cheek and palate are shown to be kinetic and mobile. Each of these features represent a departure from assumed osteolepiform models of feeding, which is not reflected in the relatively plesiomorphic morphology of the lower jaws. On the basis on convergent features shared with lepisosteid gars, the second section of this work documents the feeding mechanism of the alligator gar, Atractosteus spatula, using high-speed videography, contrast-enhanced µCT, and cranial linkage modeling. The feeding system of Atractosteus spatula incorporates elements of both jaw-ram and suction into the feeding strike, which is possible due to an unexpectedly expansive feeding mechanism and decoupling of kinematic events with plesiomorphic hyoid constrictors. The final section of this work demonstrates that the feeding mechanism of Tiktaalik roseae permitted a feeding strike similar to alligator gars, using a digitally reconstructed cranial linkage system, gar feeding kinematics, and conservative estimates of tetrapodomorph muscular anatomy. Many of the elements of a terrestrial-style feeding system are demonstrated to be possible using the feeding apparatus of Tiktaalik roseae, which gars convergently evolved in an aquatic context. This suggests that components of the terrestrial-tetrapod feeding mechanism, such as delayed hyoid depression, predominantly biting-based prey capture, and a gape cycle capable of anterior-to-posterior movements, could have evolved first in water, without the need for a terrestrial stage. Many aspects of the feeding system of Tiktaalik roseae could have subsequently been exapted for use on land by the earliest terrestrial vertebrates.

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