Monophyly, phylogeny and systematic position of the †Synechodontiformes (Chondrichthyes, Neoselachii)

Klug, S. (2009). Monophyly, phylogeny and systematic position of the ?Synechodontiformes (Chondrichthyes, Neoselachii). — Zoologica Scripta, 39 , 37–49.
Identifying the monophyly and systematic position of extinct sharks is one of the major challenges in reconstructing the phylogeny and evolutionary history of sharks in general. Although great progress has been accomplished in the last few decades with regard to resolving the interrelationships of living sharks, a comprehensive phylogeny identifying the systematic position of problematic or exclusively fossil taxa is still lacking. Fossil taxa traditionally assigned to synechodontiform sharks are very diverse with a fossil record extending back into the Palaeozoic but with uncertain inter- and intrarelationships. Here, phylogenetic analyses using robust cladistic principles are presented for the first time to evaluate the monophyly of this group, their intrarelationships and their systematic position within Neoselachii. According to the results of this study, taxa assigned to this group form a monophyletic clade, the ?Synechodontiformes. This group is sister to all living sharks and displays a suite of neoselachian characters. Consequently, the concept of neoselachian systematics needs to be enlarged to include this completely extinct group, which is considered to represent stem-group neoselachians. The origin of modern sharks can be traced back into the Late Permian (250 Mya) based on the fossil record of ?Synechodontiformes. The systematic position of batoids remains contradictory, which relates to the use of different data (molecular vs. morphological) in phylogentic analyses.