Synechodontiformes is a group of extinct sharks ranging from the Late Permian to the Palaeocene. The different views about their relationships to other elasmobranchs and interrelationships of taxa assigned to this group resulted in major controversies in recent decades because of very rare skeletal remains and very similar dental morphologies in closely related genera. Different systematic concepts were proposed, which, however, not have been tested using cladistic principles up to now.
The taxonomic and systematic revisions performed in the course of this study resulted in the recognition of a new genus, Palidiplospinax, based on skeletal remains comprising small Early and Middle Jurassic sharks. The revision of neoselachian skeletons from the Upper Jurassic lithographic limestones of South Germany yielded several new specimens and taxa and resulted in the perception that Synechodontiformes were more abundant and diversified during the Jurassic than previously assumed.
The small shark, Macrourogaleus, previously considered a cat shark, is identified as closely related to Paraorthacodus. Furthermore, the first skeleton of Late Jurassic Synechodus including a new species, S. ungeri, is described. Numerous new skeletal remains of Paraorthacodus – up to now only known from the holotype – were identified and the first complete skeleton of P. jurensis is described providing detailed information on the anatomy of these sharks. The most conspicuous differences between Paraorthacodus and Synechodus, is that Paraorthacodus has a single dorsal fin, whereas Synechodus has two dorsal fins. Differences between these two taxa and Palidiplospinax include the presence of dorsal fin spines in the latter. In addition, the taxonomic diversity of Late Cretaceous synechodontiforms from Gondwana especially from Antarctica is established.
In the course of these taxonomic revisions, abundant dental and skeletal data of synechodontiform taxa were accumulated for a subsequent phylogenetic analysis employing robust cladistic principles and a group of completely extinct taxa for the first time. The data set based on morphological characters includes a combination of previously published information and new data. Four different analyses were performed resulting in that Synechodontiforms form a monophyletic group, which is well-supported by a suite of characters and which is the basal sister group to all other neoselachians. This indicates that the systematic concept of Neoselachii must be expanded to include extinct groups that are not nested phylogenetically within Neoselachii. The ingroup interrelationships of Synechodontiformes remain largely unresolved due to the fact that several genera are only based on isolated teeth and the data set is rather restricted. It is possible to identify four cladistically well-supported monophyletic groupings including one new family, Paraorthacodontidae, consisting of Macrourogaleus and Paraorthacodus.
The new data obtained from this study enabled to review diversity and biogeographic patterns during the Jurassic as well as the timing of the first major diversification event of neoselachians in general employing statistical procedures. The most important results from these two analyses are that a first maximum of diversification is recognizable at the end of the Early Jurassic resulting in a Middle and Late Jurassic plateau and that the assumed extinction at the end of the Jurassic represents an artefact rather than a real pattern.
- Taxonomic and Systematic Background
- Dental characters of Neoselachii
- Remarks on synechodontiform monophyly
- Remarks on palaeospinacid taxonomy
Material and Methods
Results and Conclusions
Final Remarks and Future Perspectives
- List of publications part for the thesis
- Papers 1–9
Dataobject from FUDISS_thesis_000000010429
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