摘要：

Evolution in Squamata (Reptilia) focuses primarily on the phylogenetics and evolution of Varanus, commonly known as monitor lizards. Mitochondrial DNA is used to test phylogenetic hypotheses of relationships among these lizards, and the evolution of other traits of Varanus is considered in light of this hypothesis. In addition, three phylogenetic hypotheses of Anguimorpha are tested, as are the relationships among squamates, and the evolutionary origin of snakes. Chapter I reviews the taxonomy and diversity of Lepidosauria, the group containing all of the taxa of interest. Chapter II presents a phylogenetic hypothesis for Varanoidea based on mitochondrial DNA data, addresses the chromosome evolution and taxonomy of Varanus, and refutes the hypothesis that heterogeneous rates of sequence evolution are necessarily problematic to cladistic analysis. The evolutionary conclusions of Chapter II are reconsidered in Chapter III, in which the phylogenetic hypothesis is tested with additional data. The evolution of several additional morphological traits of Varanus is evaluated, as is the biogeography of Varanus and clades within it. A new taxonomy for Varanus based on this phylogenetic hypotheses is proposed. Chapter IV tests Anguimorpha and the traditionally recognized groups within it, and refutes Anguioidea, Varanoidea, and Xenosauridae. Chapter V addresses the recent controversy concerning the origin of snakes, using morphological and mitochondrial DNA evidence from basal and derived snakes and most of the groups within Squamata. Analysis of the molecular data refutes a sister group relationship between snakes and Varanus, Varanidae, or Varanoidea. The hypothesis that snakes are sister to extinct marine varanoids (mosasaurs) is refuted by simultaneous analysis of morphological and molecular data, thereby casting doubt on the inference that snakes evolved in a marine environment.

展开