Shinisaur osteology and the evolution of Squamata (Wyoming)

Lizards, snakes, and amphisbaenians (collectively, Squamata) represent a broad range of extant and fossil taxa with tremendous variation in size, form, and ecology. Squamates are found as fossils on every continent and as extant species in every country except Iceland. These characteristics make Squamata an attractive clade for studying a wide variety of biological questions. The present work details the skeletal anatomy of Shinisauridae, presents a new hypothesis of relationships for fossil and extant Squamata, and offers data regarding the application of that phylogenetic hypothesis to the questions of character evolution and biogeography.; Shinisaurus crocodilurus, the crocodile lizard, traditionally has been associated with the clade Xenosauridae. In some cases, the anatomy of Xenosaurus has been used as a proxy for that of the rare Shinisaurus. Access to well preserved specimens of Shinisaurus allows a new characterization of this species and demonstrates that Shinisaurus shares no synapomorphies with xenosaurids not shared by a wider range of taxa. The nearest relative of Shinisaurus comes from the Green River Formation (Eocene) of Wyoming. These taxa, collectively termed Shinisauridae, are the extant sister taxon to the Varanoidea.; The broader phylogenetic within Squamata have been and continue to be problematic. Incomplete taxonomic sampling is at least partly to blame for these difficulties. Broader squamate relationships are re-analyzed using a data matrix including 175 ingroup taxa scored for 334 skeletal and soft-tissue characters. Iguanians are confirmed to be the sister group to other squamates, Gekkota is the extant sister taxon to Scincomorpha and Anguimorpha, and Scincomorpha is confirmed to be monophyletic. A mostly limbless clade composed of Feyliniidae, Acontiidae, Dibamidae, Amphisbaenia, and Serpentes is shown to be nested within Scincomorpha.; Numerous character reversals are unobserved without the inclusion of many fossil forms in a phylogenetic analysis. The result is a simplified view of squamate phylogeny and character evolution.