Morphological and phylogenetic changes of the hyobranchial apparatus from fishes to basal tetrapods.

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The transformation of the hyobranchium (visceral skeleton) that requires fishes to suction feeding in water, to an apparatus that enables tongue-based terrestrial feeding, is a key aspect of the evolution of tetrapods, but is still poorly understood. The goal of this project is to recover the developmental changes of the hyobranchium during the fish-to-tetrapod transition in the Middle and Late Devonian. Several questions must be addressed including, (1) which structures of the hyobranchium of nontetrapods were conserved in basal tetrapods, (2) which were modified, and (3) how was the hyobranchium used for feeding and breathing in the different lineages of these animals? The project will focus on the morphological and phylogenetic investigation of the hyobranchial remains of Palaeozoic and Mesozoic basal tetrapods and their fish-like relatives. Two hypotheses will be tested: First, basal tetrapods retained a "fish-like" hyobranchium and fed on land by jaw prehension. Ontogenetic remodelling of the hyobranchium with the elaboration of a movable tongue skeleton evolved later in evolution, independently in the lineage leading to lissamphibians and to amniotes. Second, ontogenetic remodelling for a tongue-supporting hyobranchium evolved early in tetrapod history, and the retention of a "fish-like" hyobranchium is a paedomorphic trait. The better knowledge of phylogenetic changes of the hyobranchium would greatly improve our understanding of the fish-totetrapod transition and the origin of terrestriality in vertebrates.