Convergent evolution driven by similar feeding mechanics in balaenopterid whales and pelicans.

The feeding apparatuses of rorqual whales and pelicans exhibit a number of similarities, including long, kinetic jaws that increase gape size, and extensible tissue comprising the floor of the mouth. These specializations enable the engulfment of large volumes of prey-laden water in both taxa. However, the mechanics of engulfment feeding in rorquals and pelicans have never been quantitatively compared. Here, we use "BendCT," a novel analytical program, to investigate the mechanical design of rorqual and pelican mandibles, to understand whether these bones show comparable designs for resisting similar hydrodynamical loads. We also compare the mechanical properties of the extensible tissue used during engulfment in rorquals and pelicans. We demonstrate that the evolutionary convergence in the feeding apparatus of rorquals and pelicans is more pronounced than has been recognized previously; both taxa exhibit mandibular flexural rigidity distributions suited for resisting dorsoventral bending stresses encountered while feeding, and possess similarly extensible tissue on the floor of their mouths.