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Armored skin resulting from the presence of bony dermal structures, osteoderms, is an exceptional phenotype in gekkotans (geckos and flap‐footed lizards) only known to occur in three genera:Geckolepis,Gekko, andTarentola. The Tokay gecko (Gekko geckoLINNAEUS 1758) is among the best‐studied geckos due to its large size and wide range of occurrence, and although cranial dermal bone development has previously been investigated, details of osteoderm development along a size gradient remain less well‐known. Likewise, a comparative survey of additional species within the broaderGekkoclade to determine the uniqueness of this trait has not yet been completed. Here, we studied a large sample of gekkotans (38 spp.), including 18 specimens ofG. gecko, using X‐rays and high‐resolution computed tomography for visualizing and quantifying the dermal armorin situ. Results from this survey confirm the presence of osteoderms in a second species within this genus,GekkoreevesiiGRAY 1831, which exhibits discordance in timing and pattern of osteoderm development when compared with its sister taxon,G. gecko. We discuss the developmental sequence of osteoderms in these two species and explore in detail the formation and functionality of these enigmatic dermal ossifications. Finally, we conducted a comparative analysis of endolymphatic sacs in a wide array of gekkotans to explore previous ideas regarding the role of osteoderms as calcium reservoirs. We found thatG. geckoand other gecko species with osteoderms have highly enlarged endolymphatic sacs relative to their body size, when compared to species without osteoderms, which implies that these membranous structures might fulfill a major role of calcium storage even in species with osteoderms.

 

1935 gecko species (and 224 subspecies) were known in December 2019 in seven families and 124 genera. These nearly 2000 species were described by ~950 individuals of whom more than 100 described more than 10 gecko species each. Most gecko species were discovered during the past 40 years. The primary type specimens of all currently recognized geckos (including subspecies) are distributed over 161 collections worldwide, with 20 collections having about two thirds of all primary types. The primary type specimens of about 40 gecko taxa have been lost or unknown. The phylogeny of geckos is well studied, with DNA sequences being available for ~76% of all geckos (compared to ~63% in other reptiles) and morphological characters now being collected in databases. Geographically, geckos occur on five continents and many islands but are most species-rich in Australasia (which also houses the greatest diversity of family-level taxa), Southeast Asia, Africa, Madagascar, and the West Indies. Among countries, Australia has the highest number of geckos (241 species), with India, Madagascar, and Malaysia being the only other countries with more than 100 described species each. As expected, when correcting for land area, countries outside the tropics have fewer geckos.