TAILIEUCHUNG - Linzey - Vertebrate Biology - Chapter 7

C H A P T E R 7 Evolution of Reptiles The class Reptilia is no longer recognized by phylogenetic systematists, because it is not a monophyletic group. Traditionally, the class Reptilia included the turtles, tuatara, lizards, snakes, and crocodilians. | Linzey Vertebrate Biology 7. Evolution of Reptiles I Text The McGraw-Hill Companies 2003 CHAPTER 7 Evolution of Reptiles INTRODUCTION The class Reptilia is no longer recognized by phylogenetic systematises because it is not a monophyletic group. Traditionally the class Reptilia included the turtles tuatara lizards snakes and crocodilians. Birds which descend from the most recent common ancestor of reptiles have traditionally been classified by themselves in the class Aves. Reptiles therefore are a paraphyletic group unless birds are included. Furthermore based on shared derived characteristics crocodilians and birds are more recently descended from a common ancestor than either is from any living reptilian lineage thus they are sister groups. In phylogenetic systematics cladistics turtles tuataras lizards snakes crocodilians and birds are placed in the monophyletic group Sauropsida. The Sauropsida include three groups turtles Testudomorpha tuataras lizards and snakes Lepidosauromorpha and the crocodilians and birds Archosauromorpha . In this method of classification turtles are placed at the base of the tree. New evidence from 2 nuclear genes and analyses of mitochondrial DNA and 22 additional nuclear genes join crocodilians with turtles and place squamates at the base of the tree Hedges and Poling 1999 Rieppel 1999 . Morphological and paleontological evidence for this phylogeny are unclear at the present time. Considerable disagreement continues between proponents of evolutionary traditional taxonomy and cladistics. The classification used in this text for the most part will follow the cladistic method. Comparisons between the two classification methods will be presented at appropriate points. For ease of discussion we will divide the reptiles sauropsids into two chapters Evolution this chapter and Morphology Reproduction and Growth and Development Chapter 8 . EVOLUTION The fossil record for reptiles is much more complete than the one for amphibians. Based on .