The gustatory stalk of the Remo flounder exemplifies how complex evolutionary novelties may arise.

The appearance of evolutionary novelties is a central issue in biology. Since Darwin's theory, difficulties in explaining how novel intricate body parts arose have often been used by creationists and other deniers to challenge evolution. Here, we describe the gustatory stalk of the Remo flounder (Oncopterus darwinii), an anatomically and functionally complex organ presumably used as a chemoreceptor probe to detect prey buried in the substrate. We demonstrate that the gustatory stalk is derived from the first dorsal-fin ray, which acquired remarkable modifications in its external morphology, integument, skeleton, muscles, and nerves. Such structural innovations are echoed in both functional and ecological specializations. We reveal that the gustatory stalk arose through the gradual accumulation of changes that evolved at different levels of the phylogenetic tree of ray-finned fishes. At least five preconditions arose in nodes preceding Oncopterus darwinii. This finding constitutes an interesting example of how evolution can deeply remodel body parts to perform entirely new functions. In this case, a trivial support structure primitively used for swimming became a sophisticated sensory tool to uncover hidden prey.