Stranger things: on the novel buccopharyngeal anatomy and functional morphology of ‘sand-eating’ Malagasy tadpoles (Anura: Mantellidae: Mantidactylus)

Anuran larvae are characterized by an extensive array of specialized oral structures that allow them to both graze on substrates and suspension feed with great efficiency. Diversity in these feeding structures accounts for significant diversity of anurans. Herein we describe an astonishing novel buccopharyngeal morphology in six larvae of ‘sand-eating’ tadpoles of the Mantellidae genus Mantidactylus. The buccopharyngeal cavity of these tadpoles is characterized by the presence of ruffled ridges not seen previously in any other anuran larva. Extensive review of the literature and of new empirical data demonstrates the uniqueness of this morphology. We present both CT scans and ergonomic arguments in support of the hypothesis that the ruffled ridges are employed as scrubbing pads, allowing these tadpoles to remove food particles from sand grains. In addition, we explore how the ridges may have developed and evolved.