Characteristics of miniaturization in squamates: A phylogenetic perspective from cranial morphology

Miniaturization is recurrent in tetrapods, and has been widely recognized to be an evolutionary process resulting from the occupation of previously unexploited niches (Hanken and Wake, 1993; Rieppel, 1984a, 1996). In this thesis I review the process of miniaturization and its effects on the skull of squamates (lizards, snakes, and amphisbaenians). I compiled a list of characteristics previously described for squamates and summarized the main differences among higher level groups (e.g., Iguania, Gekkota or Scincomorpha). I also investigated whether observed traits linked to miniaturization are the product of convergent evolution. I used a large published morphological data set that includes 204 species of which 54 are miniaturized. I coded characters for an additional species that represent the smallest known squamates (e.g., Sphaerodactylus ariasae and Brookesia micra) and belong to taxonomic groups with minor representation in the original dataset. Analyses identified two characters that occurred in miniaturized taxa of 15 mm or less in skull length, six characteristics for species with 10 mm or less, three for species with 5 mm or less, and eight traits convergent to miniaturized head-first burrowers.