The evolution of Cephalopods and their present biodiversity and ecology
The present status of phylogeny and classification in coleoid cephalopods and the effect of evolution on the present ecology and biodiversity in the group are examined. The basis of knowledge of cephalopod phylogeny was formulated by Naef in the early 1920s, and his ideas and the progress made in the intervening 75 years are investigated. In the process, the roles that transitions between pelagic and benthic habitats played in the evolution of cephalopods are noted, and the possibility is advanced that the most recent "oceanic anoxic event" may have established a time marker for the divergence of some oegopsid families. The major advances since Naef's work are: 1. The unusual nature of Vampyroteuthis has been recognized; 2. The sister-group relationship between the Neocoleoidea and the Belemnoidea has been established, but requires further confirmation; 3. Monophyly has been confirmed for the Decapodiformes (new name), Octopodiformes and Octopoda by molecular and morphological methodologies; 4. The dates of origin of the Belemnoidea, Neocoleoidea, Sepioidea and fossil teuthoids have been extended to considerably earlier times. The major unsolved phylogenetic problems in need of immediate attention are the position of the Myopsida, relationships within the Sepioidea, the identification of the basal nodes within the Oegopsida, and the relationships of most "fossil teuthoids."