Phylogeny of the spiny lizards (Sceloporus) based on molecular and morphological evidence

Relationships within the phrynosomatid lizard genus Sceloporus are estimated using parsimony analysis of molecular and morphological data. The data include DNA sequences from the mitochondrial 12S and 16S ribosomal RNA genes (262 informative characters) obtained for 64 ingroup taxa, and morphological characters (202 informative characters describing variation in osteology, squamation, coloration, karyology, and life history) scored for 109 ingroup taxa. The molecular data set includes representatives of all of Smith's species groups as well as the genus Sator, and the morphological data set includes Sator and nearly all the recognized species and distinctive subspecies of Sceloporus. The data sets are analyzed separately and in combination, and the single, fully resolved tree from the simultaneous analysis of all the taxa and characters is taken as the best estimate of phylogeny and the basis for a revised classification. The genus Sator is nested inside Sceloporus (as the sister taxon of the utiformis and siniferus species groups), and is classified within Sceloporus as the angustus species group. The traditional division of Sceloporus into large-scaled and small-scaled radiations is not supported; the small-scaled species form a graded series of lineages leading up to a clade of mostly large-scaled species, and this clade contains the putatively small-scaled scalaris species group. Most of the species groups recognized in Hobart Smith's 1939 monograph are upheld by this study (with or without minor modifications), but the polyphyletic "spinosus" zspecies group is dismantled into six monophyletic groups. A general pattern of strong character support for the monophyly of species groups but weak support for the relationships between them occurs in the trees from the molecular, morphological, and combined data sets; this congruent pattern is most likely the result of rapid speciation.