Locomotion and paleoclimate explain the re-evolution of quadrupedal body form in Brachymeles lizards

Evolutionary reversals, including re-evolution of lost structures, are commonly found in phylogenetic studies. However, we lack an understanding of how these reversals happen mechanistically. A snake-like body form has evolved many times in vertebrates, and occasionally, a quadrupedal form has re-evolved, including in Brachymeles lizards. We use body form and locomotion data for species ranging from snake-like to quadrupedal to address how a quadrupedal form could re-evolve. We show that large, quadrupedal species are faster at burying and surface locomotion than snake-like species, indicating a lack of expected performance trade-off. Species with limbs use them while burying, suggesting that limbs are useful for burying in wet, packed substrates. Paleoclimatological data suggest that Brachymeles originally evolved a snake-like form under a drier climate likely with soil in which it was easier to dig. The quadrupedal clade evolved as the climate became humid, where limbs and large size ...