Integrative taxonomy of Madagascar’s sand-swimming skinks (Scincidae: <i>Voeltzkowia</i> , <i>Grandidierina</i> ) and preliminary evidence for an overlooked inland belt of white sand patches across the island’s west

Abstract Malagasy sand-swimming skinks represent several highly specialized and previously underexplored clades within the monophyletic radiation of scincine lizards of this island. Through comprehensive phylogenomic analyses including newly collected samples, we clarify the evolutionary relationships among these taxa, delimit species boundaries, and formally describe two new species: Voeltzkowia volontany sp. nov. and Voeltzkowia shaihulud sp. nov. Our findings on the genus Voeltzkowia and the equally specialized sand-swimmer genus Grandidierina suggest that species diversity within these psammophilous skinks is underestimated and shaped by a high degree of allopatry. Intriguingly, this unexpected diversity is geographically structured along a newly identified landscape feature, for which we herein coin the name ‘White Sand Belt’. It consists of an aligned series of discrete, isolated white sand patches spanning &amp;gt;1500 km along western Madagascar. The White Sand Belt appears to follow the contours of the western sedimentary basins of the island, and we propose the hypothesis that it represents a key environmental factor in the diversification and distribution of Malagasy sand-swimming skinks and, possibly, other psammophilous organisms.