A database of the morphology, ecology and literature of the world's limb-reduced skinks

Abstract

Aim: Limb- reduced squamates are a convenient model system to investigate macroevolu-tionary trends in morphology. Here, we provide morphological, ecological and literature data on all known species of limb- reduced skinks (Scincidae) and their relatives, represent-ing one of the most diverse and widely distributed groups of limb- reduced squamates.Location: Global.Ta xo n: Skinks (Reptilia, Squamata: Scincidae). Limb- reduced forms.Methods: Morphological data were sourced from the primary literature, spanning a period of over 150 years. Linear body measurements were averaged across all values in the literature, preserving proportionality to body length. For digits and presacral vertebrae, we used maximum recorded counts. Ecological and biogeographical data were sourced from habitat assessments in the primary literature, online databases and field guides. Literature data were sorted according to type of study. To exemplify the applicability of the database, we used Markov-chain ordered models to estimate the evolutionary frequency of limb reduction and loss in skinks.Results: We find evidence of limb reduction and loss in a total of 394 species world-wide, representing ~23% of all skink species, and ~30% of genera. The distribution of limb- reduced and limbless forms differs from that of fully limbed forms, as they are present in all biogeographic realms with the almost complete exclusion of the Americas. We estimate that limb reduction evolved more than 50 times in skinks, and that loss of at least one limb pair evolved at least 24 times.Main conclusions: The dataset captures a broad spectrum of morphological and ecological variation in a large, globally distributed taxonomic group. It establishes a widely applicable definition of limb reduction based on limb proportions as a reference for future studies. Such an extensive collection of morphological and ecological data can pave the way for investigations of dramatic morphological transitions and their ecological drivers at a global and local scale.