The early Mesozoic has recently received much attention with respect to the recovery of marine life from the greatest ever (end-Permian) extinction event and another major extinction event at the end of the Triassic (overviews in Erwin, 2006; Smith, 2007; and references therein). The Permian/Triassic Boundary (PTB) in particular may play a pivotal role in assessing putative cause-and-effect scenarios during the Palaeozoic-Mesozoic transition (Algeo et al., 2007). However, ‘sh species-normally

6.1 Introduction .................................................................................................. 143 6.1.1 Previous Phylogenetic Studies .......................................................... 146

6.2 Material and Methods ................................................................................... 147 6.2.1 Phylogenetic Analyses ...................................................................... 147 6.2.2 Systematic Palaeontology ................................................................. 147

6.2.2.1 Family Diagnosis ............................................................... 147 6.2.2.2 Occurrence ......................................................................... 149

6.3 Phylogenetic Analysis ................................................................................... 150 6.4 Discussion of Ptycholepid Intrarelationships and Palaeobiogeographic

Analysis ........................................................................................................ 152 6.5 Conclusions ................................................................................................... 158 Acknowledgements ................................................................................................ 160 Appendix 6A: List of Characters Used in Phylogenetic Analysis ......................... 160 Appendix 6B: Ptycholepid Intrarelationships-List of Characters and Analysis ........................................................................................................... 162 Analysis .................................................................................................................. 163 Literature Cited ...................................................................................................... 167

making up at least 50% of the fossil record of vertebrates and a key to understanding the Palaeozoic-Mesozoic faunal turnover-are remarkably rare in PTB localities, yet quite abundant in a number of classical localities of Late Permian and early Mesozoic age. Due to the scarcity or even absence of ‘sh remains in known PTB sections and rocks immediately on either side of the PTB, these Permian-Triassic localities have recently attracted considerable scienti‘c attention. At the family level (Pitrat, 1973; Schaeffer, 1973; Benton, 1993), the composition of the respective ichthyofaunas seems to be fundamentally different. And indeed, numerous Triassic ‘sh genera cannot be traced back to Palaeozoic ancestors, whereas ichthyofauna diversity increased during the early Middle Triassic (Mutter, 2003).