section_path: Classification/Traditional classification
section_name: Traditional classification
paragraph_text: Traditional classification
  
  Conventional classification has living vertebrates grouped into seven classes based on traditional interpretations of gross anatomical and physiological traits. This classification is the one most commonly encountered in school textbooks, overviews, non-specialist, and popular works. The extant vertebrates are:
  
  In addition to these, there are two classes of extinct armoured fishes, the Placodermi and the Acanthodii, both considered paraphyletic.
  
  Other ways of classifying the vertebrates have been devised, particularly with emphasis on the phylogeny of early amphibians and reptiles. An example based on Janvier (1981, 1997), Shu et al. (2003), and Benton (2004) is given here († = extinct):
  
  While this traditional classification is orderly, most of the groups are paraphyletic, i.e. do not contain all descendants of the class's common ancestor. For instance, descendants of the first reptiles include modern reptiles, mammals and birds; the agnathans have given rise to the jawed vertebrates; the bony fishes have given rise to the land vertebrates; the traditional " amphibians " have given rise to the reptiles (traditionally including the synapsids or mammal-like "reptiles"), which in turn have given rise to the mammals and birds. Most scientists working with vertebrates use a classification based purely on phylogeny, organized by their known evolutionary history and sometimes disregarding the conventional interpretations of their anatomy and physiology.