The Fragmentation of Gondwanaland: Influence on the Historical Biogeography and Morphological Evolution within Dragon Lizards (Squamata: Agamidae)

Abstract

Following the break up of the Pangaea, landmasses were aggregated into two super-continents, Laurasia in the northern hemisphere and Gondwanaland in the southern hemisphere. Both have been considered ancestral areas where many of today’s taxonomic groups originated. However, during the Devonian, Gondwanaland began to fragment with micro-continental blocks breaking and rafting northwestwards across the Tethys Sea. These micro-continents eventually collided into Laurasia transforming into what today is Southeast Asia and parts of Wallacea. These micro-continental blocks carried Gondwanan lineages that evolved in isolation as they rafted across the Tethys Sea and subsequently dispersed into Laurasia. This geologic scenario has been used to explain why there are Asian lineages of lizards, birds, fish, and land snails that are more closely related to Australian and Papuan taxa than they are to other Asian lineages. One well-documented case of this biogeographic hypothesis is with Dragon Lizards. There have been two previous comprehensive studies on Dragon Lizard relationships, one based on discrete morphological characters and one using molecular data, and both predicted Gondwanan origins for all Dragon Lizards commensurate with the geologic scenario outlined above. Both studies, however, were based on limited sampling and reported problematic relationships that hindered their ability to unequivocally explain the geographic and evolutionary origins of this lizard family. In this dissertation, I use phylogenomic data to resolve long-standing contentious Dragon Lizard relationships in order to revisit hypotheses of their Gondwanan origins and Tethys Sea migrations. I first use this phylogeny to test the hypothesis of an Indian (Gondwanan) origin for Southeast Asian Dragon Lizards and reevaluate the colonization of the Indian and the Indo-Himalaya regions. Once these problematic relationships and biogeographic origins were resolved, it enabled me to use unprecedented taxonomic sampling to provide the first estimate of a Dragon Lizard tree of life in order to test previous published hypotheses of Gondwanan origins and the morphological evolution within Dragon Lizards. Lastly, I use a dataset of 122 discrete morphological characters from a previous study and sum the number of unambiguous synapomorphies in the cranial and post-cranial skeletal characters associated with cephalic and axial body modifications in lineages that have morphological specializations in these regions. Lastly, I use the Dragon Lizard Tree of Life and these synapomorphies to perform a phylogenetic logistic regression analysis to show that the evolution of the higher number of relative synapomorphies associated with cephalic and axial body modifications are phylogenetically independent of one another. This study contributes to our knowledge of Gondwanan and Laurasian biogeography as well as how shared environmental pressures affect the external and internal morphology of unrelated species within Dragon lizards.