{Note: I intend to append a short glossary to the end of this text in order to explain
technical terms [in boldface] for the non-systematics geeks.}
An aspect of what is known as the "tetrapod problem" is the focus of this study. Specifically, I am examining a longstanding controversy—the relationships among the amniotes. Early attempts to classify organisms into natural groups (in a non-evolutionary context) provided a hypothesis of (turtle,(mammal,((snake,lizard),(crocodilian,(bird)))). Recent studies have recognized that the turtle and mammal positions on this traditional hypothesis are reversed, and this modified version has gained wide acceptance among systematists. However, Gardiner published a paper in the Zoological Journal of the Linnean Society in 1982 challenging this hypothesis. His unorthodox view gained support among some (notably Løvtrup [1985]) and was dismissed out of hand by others (notably Devillers and de Ricqlés [1982]). Six years later, Gauthier and his collaborators published a rebuttal in Cladistics, using a considerably larger data matrix and including fossil taxa (an idea to which Gardiner was adamantly opposed). Since then, a number of investigators have attempted to address this issue using a variety of molecular sequence data, but the last comprehensive review was undertaken by Eernisse and Kluge in 1993. My thesis updates and supplements this work by adding 28S ribosomal DNA data for a representative bird and crocodilian, as I seek a definitive answer for Kemp's (1988) question: Haemothermia or Archosauria? The 28S data and the combined data matrix favor the Archosauria hypothesis.
©1999 Brian R. Warren