Four new lepidosaurs from the Early Cretaceous deposits of the Tlayua Quarry, Central Mexico are described, establishing their phylogenetic relationships using cladistic methodology. These lepidosaurs have unique characters never present in related forms suggesting that they have evolved in isolated environments far from immediate ancestors, indicating the insular nature of the quarry. The sphenodontid Pamizinsaurus tlayuaensis is covered with unique rows of small rounded osteoderms that could have protected it against predation in open environments. Ankylosphenodon pachyostoseus has unusual teeth ankylosed deep into the dentary with probable continuous growth, which combined with propalinal action of a deep lower jaw suggest herbivory. Unique pachyostotic ribs and vertebrae, delay in the ossification of the epiphyses, and zygapophyses horizontally oriented to stiffen the vertebral column could be related to aquatic behavior. The unique morphology of Pamizinsaurus and Ankylosphenodon argue against the concept of low morphological diversification of sphenodontians. / The lizard Huehuecuetzpalli mixtecus shows most iguanian features, but still retains a divided premaxilla, amphicoelous vertebrae, thoracolumbar intercentra, and the second distal tarsal, supporting a phylogenetic position as sister-group of squamates. Although late in the fossil record, Huehuecuetzpalli provides important information on early transformation of characters in lizard evolution. Tepexisaurus tepexii is an early scincomorph relatively more primitive to all known scincoids. The lack of osteoderms indicates that Tepexisaurus and some paramacellodids are not scincoids, suggesting that the Paramacellodidae is not monophyletic. The relative primitive morphology of Tepexisaurus in Albian deposits can be correlated with the late presence of sphenodontians and the relictual nature of Huehuecuetzpalli in Tlayua. This suggests that TIayua was a refuge for archaic terrestrial forms. / Character transformation at the origin of the Squamata was explored through a phylogenetic analysis including basal lepidosauromorphs, the best known early squamates, and extant squamate "families". Results using a rigorously reviewed data set, show that many characters suggested to be squamate autapomorphies are certainly along a lineage basal to the Squamata, which includes Marmoretta, Tamaulipasaurus, the Ardeosauridae (redefined to include Bavarisaurus), and Huehuecuetzpalli. The name Squamatoidea to group all taxa basal to Squamata + squamates is suggested. The Total Branch Support index obtained falls between values of other published phylogenies. The low values seem to be affected by the inclusion of several fossil taxa with incomplete information and the redistribution of a limited number of characters in a greater number of branches.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.34437 |
| Date | January 1996 |
| Creators | Reynoso, Víctor-Hugo. |
| Contributors | Carroll, R. L. (advisor) |
| Publisher | McGill University |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Format | application/pdf |
| Coverage | Doctor of Philosophy (Department of Biology.) |
| Rights | All items in eScholarship@McGill are protected by copyright with all rights reserved unless otherwise indicated. |
| Relation | alephsysno: 001564118, proquestno: NQ30369, Theses scanned by UMI/ProQuest. |
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