Evolution and role of the follicular epidermal gland system in non-ophidian squamates

Many lizard and amphisbaenian lineages possess follicular glands in the dermis of the inner thighs and/or the area anterior to the cloaca. These tubular glands produce a holocrine secretion that finds its way to the external world through pore-bearing scales (femoral and/or preanal pores). Secretions are composed of proteins and many lipophilic compounds that may function as chemosignals in lizard and amphisbaenian communication. In recent years, we have begun to develop an understanding of the adaptive significance of these secretions, and they are currently thought to play an important role in a variety of processes in these animals. While it appears that epidermal gland secretions function in intra- and interspecific recognition and territoriality, research has focused largely on their role in mate assessment. Despite these recent studies, our knowledge on the true role of the chemicals found in epidermal secretions remains poorly studied, and there are many possible avenues for future research on this topic. Here, we review the literature on the follicular epidermal glands of non-ophidian squamates and provide a first taxon-wide overview of their distribution.