The scratch-digging lifestyle of the Permian “microsaur” Batropetes Carroll & Gaskill, 1971 as a model for the exaptative origin of jumping locomotion in frogs

Abstract

Recent studies have shown that the Triassic stem-frog Triadobatrachus Kuhn, 1962 lacked the ability to jump, but nonetheless had the forelimb strength to withstand the impact of landing from a jump. We propose a hypothesis to resolve this pseudoparadox: the strengthened forelimbs are former adaptations to forelimb-based digging that later made jumping possible by exaptation. Micro-CT data from a skeleton of Batropetes palatinus Glienke, 2015 reveal thin cortical bone, confirming Batropetes Carroll & Gaskill, 1971 as terrestrial. Combining adaptations to walking and digging, confirmed by statistical analyses, Batropetes is thought to have searched for food in leaf litter or topsoil. We interpret Batropetes as having used one forelimb at a time to shove leaf litter aside. Batropetes may thus represent an analog, or possibly a homolog, of the digging stage that preceded the origin of Salientia Laurenti, 1768. We discuss the possibility of homology with the digging lifestyles of other “microsaurs” and other amphibians.