Diapsid Phylogeny and the Origin and Early Evolution of Squamates

• Author / Creator

  Rodrigues Simões, Tiago

• Squamate reptiles comprise over 10,000 living species and hundreds of fossil species of lizards, snakes and amphisbaenians, with their origins dating back at least as far back as the Middle Jurassic. Despite this enormous diversity and a long evolutionary history, numerous fundamental questions remain to be answered regarding the early evolution and origin of this major clade of tetrapods. Such long-standing issues include identifying the oldest fossil squamate, when exactly did squamates originate, and why morphological and molecular analyses of squamate evolution have strong disagreements on fundamental aspects of the squamate tree of life. Additionally, despite much debate, there is no existing consensus over the composition of the Lepidosauromorpha (the clade that includes squamates and their sister taxon, the Rhynchocephalia), making the squamate origin problem part of a broader and more complex reptile phylogeny issue. In this thesis, I provide a series of taxonomic, phylogenetic, biogeographic and morpho-functional contributions to shed light on these problems. I describe a new taxon that overwhelms previous hypothesis of iguanian biogeography and evolution in Gondwana (Gueragama sulamericana). I re-describe and assess the functional morphology of some of the oldest known articulated lizards in the world (Eichstaettisaurus schroederi and Ardeosaurus digitatellus), providing clues to the ancestry of geckoes, and the early evolution of their scansorial behaviour. I also provide a re-description and considerations on ontogeny and sexual dimorphism in the most complete Cretaceous lizard from North America (Polyglyphanodon sternbergi), followed by a biomechanical study on the function of the lower temporal bar in squamates, and a case of non-adaptive reacquisition of this structure in borioteiioids. As the groundwork for my phylogenetic dataset, I provide a thorough discussion on morphological dataset construction for phylogenetic analysis, including a set of basic criteria to be followed in order to avoid logical and biological biases in morphological characters. This is followed by a detailed revision of nearly 1,000 characters previously proposed for squamate phylogenies. In my final chapter, I introduce data personally collected by me over the course of 400 days of collection visits on all major lineages of diapsid reptiles and squamates. I analyse these morphological data along with molecular data obtained from online repositories and provide a new diapsid reptile phylogeny tested under distinct optimality criteria, also being the first with a deep sampling of squamates lineages. I find the first ever agreement between morphological and molecular data regarding the early evolution of squamates, and evidence that the Middle Triassic reptile Megachirella wachtleri represents the oldest known fossil squamate in the world. I implement the latest developments in divergence time estimation under relaxed clock Bayesian inference upon this dataset, and I find that the origin of the major diapsid clades, including lepidosaurs, lies prior to the Permian-Triassic extinction event. This revises previous ideas that the origin of lepidosaurs, archosaurs, and other important diapsid lineages happened in the Triassic, and indicates that, rather than triggering their origin, the Permian-Triassic Mass extinction triggered the diversification of already existing diapsid lineages.

• Subjects / Keywords

  • morphological clocks
  • Phylogenetics
  • combined evidence
  • squamates
  • reptiles

• Graduation date

  Fall 2018

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R3HT2GT60

• License

  Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.