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

Abstract

Klug, S. (2010). Monophyly, phylogeny and systematic position of the †Synechodontifor-mes (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.

Node age estimations and the origin of angel sharks, Squatiniformes (Neoselachii, Squalomorphii)

“…Almost all of these dates are now obsolete with better resolution of the fossil record of sharks (e.g. Klug 2010).…”

A new Jurassic cow shark (Chondrichthyes, Hexanchiformes) with comments on Jurassic hexanchiform systematics

“…nov. to some extent, but the teeth are readily distinguishable by different features. The tooth root of synechodontiforms, which is comparably low, is characterized by a pseudopolyaulacorhize vascularization pattern, and displays a labial depression in basal view, which is lacking in hexanchiforms (Klug 2010). Additionally the morphology of the tooth crown of pseudonotidanids presents a divergent pattern of the main cusp and the first distal cusplet (Klug and Kriwet 2010).…”

“…The tooth crown morphology of the neoselachian stemlineage Synechodontiformes (Klug 2010), especially of the family Pseudonotidanidae, resembles that of hexanchiform sharks including Crassonotidae fam. nov. to some extent, but the teeth are readily distinguishable by different features.…”

A new Late Jurassic species of the rare synechodontiform shark, Welcommia (Chondrichthyes, Neoselachii)

“…Identification of stem-lineage representatives, conversely, is more difficult. So far, Synechodontiformes is the only stem-lineage group that has been recognized and defined using cladistic principles (Klug 2010). Members of Synechodontiformes are characterized by a combination of plesiomorphic and derived characters and include at least 11 genera (Mucrovenator, Rhomphaiodon, Welcommia, Pseudonotidanus, Sphenodus, ''pre-Jurassic Synechodus'' (e.g.…”