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

Aim: Limb-reduced squamates are a convenient model system to investigate macroevolutionary trends in morphology. Here, we provide morphological, ecological and literature data on all known species of limb-reduced skinks (Scincidae) and their relatives, representing one of the most diverse and widely distributed groups of limb-reduced squamates. Location: Global. Taxon: 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 worldwide, representing similar to 23% of all skink species, and similar to 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.

Automated summary

This study provides morphological, ecological, and literature data on limb-reduced skinks and their relatives. Limb reduction and loss are found in a total of 394 species worldwide, representing about 23% of all skink species and about 30% of genera. The distribution of limb-reduced and limbless forms differs from fully limbed forms, with their presence in all biogeographic realms except the Americas. The study estimates that limb reduction evolved more than 50 times and loss of at least one limb pair evolved at least 24 times in skinks.