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A Phylogenetic Appraisal of Pachycormus Bollensis

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A Phylogenetic Appraisal of Pachycormus Bollensis Självständigt arbete Nr 31 A Phylogenetic Appraisal of Pachycormus bollensis: Implications for Pachycormiform Evolution A Phylogenetic Appraisal of Maria Lindkvist Pachycormus bollensis: Implications for The Pachycormiformes were a successful group of stem-teleosts. Although they persisted for more than 100 million years in the Pachycormiform Evolution Mesozoic seas and occupied a significant space of the ecosystem, little is known about this most diverse group. One of the earliest pachycormiformes is the lower Jurassic Pachycormus bollensis. A reconstruction of the phylogeny with the early P. bollensis together with more derived and earlier studied species has yielded important information about the relationships within the group. Both a parsimony analysis and a Bayesian analysis were performed. Three Maria Lindkvist exceptionally complete specimens of P. bollensis from the Holzmaden-locality were used for the study. The resulting trees strongly supported pachycormiform monophyly. Three major ecomorphological clades were returned from the analyses: the filter- feeders, hyper carnivores and a more generalist predator radiation that included P. bollensis. Despite, node support within the pachycormiformes are generally weak. The tooth-structure and the phylogenetic position of P. bollensis might indicate an intermediate grade between the filter-feeders and the hyper carnivores. Uppsala universitet, Institutionen för geovetenskaper Kandidatexamen i Geovetenskap, 180 hp Självständigt arbete i geovetenskap, 15 hp Tryckt hos Institutionen för geovetenskaper Geotryckeriet, Uppsala universitet, Uppsala, 2012. Självständigt arbete Nr 31 A Phylogenetic Appraisal of Pachycormus bollensis: Implications for Pachycormiform Evolution Maria Lindkvist Supervisor: Benjamin Kear Abstract The Pachycormiformes were a successful group of stem-teleosts. Although they persisted for more than 100 million years in the Mesozoic seas and occupied a significant space of the ecosystem, little is known about this most diverse group. One of the earliest pachycormiformes is the lower Jurassic Pachycormus bollensis. A reconstruction of the phylogeny with the early P. bollensis together with more derived and earlier studied species has yielded important information about the relationships within the group. Both a parsimony analysis and a Bayesian analysis were performed. Three exceptionally complete specimens of P. bollensis from the Holzmaden-locality were used for the study. The resulting trees strongly supported pachycormiform monophyly. Three major ecomorphological clades were returned from the analyses: the filter-feeders, hyper carnivores and a more generalist predator radiation that included P. bollensis. Despite, node support within the pachycormiformes are generally weak. The tooth-structure and the phylogenetic position of P. bollensis might indicate an intermediate grade between the filter-feeders and the hyper carnivores. Sammanfattning Pachycormiformer var en mycket framgångsrik ordning utav stam-teleoster. Trots att de överlevde i mer än 100 miljoner år i de Mesosoiska haven och erövrat ett flertal olika platser i ekosystemet, är denna mågfacetterade grupp som helhet tämligen okänd. Pachycormus bollensis från yngre jura är en av de tidigste arterna i denna grupp. En fylogenetiskt rekonstruktion av den tidiga P. bollensis tillsammans med yngre, mer utvecklade arter kan ge viktig information om släktskapen inom gruppen. En parsimonisk analys och en Bayesian analys utfördes. Tre exceptionellt bevarade exemplar av Pachycormus bollensis från Holzmaden användes i studien. Resultatet visar på ett stark monofyletiskt sammanband inom pachycormiformerna. Båda analyserna visade robusta resultat för tre övergripande grupper; filtrerare, karnivorer och en mer generell predator linje som inkluderar P. bollensis. Dock hade de interna släktskapen inom varje större grupp svagt stöd. Tand-stukturen tillsammans med den fylogenetiska placeringen av P. bollensis kan tyda på en intermediär grupp mellan filterarna och karnivorerna. Table of Contents 1. Introduction ..................................................................................................................................... 5 1.1 The Pachycormiformes .................................................................................................................. 5 1.2 Geology of Holzmaden – the Posidonia Shale ............................................................................... 6 2. Materials and methods ................................................................................................................... 7 2.1 Phylogenetic methods ................................................................................................................... 7 2.2 The parsimony analysis ................................................................................................................. 7 2.3 The Bayesian analysis .................................................................................................................... 8 2.4 Source specimens .......................................................................................................................... 9 3. Results and discussion ................................................................................................................... 10 3.1 Parsimony analysis ...................................................................................................................... 10 3.1.1 Nodal support ....................................................................................................................... 10 3.1.2 Character evolution .............................................................................................................. 11 3.2 Bayesian analysis ......................................................................................................................... 14 3.3 Discussion of Matt Friedman et al. (2010) .................................................................................. 15 4. Conclusions .................................................................................................................................... 17 5. Acknowledgement ......................................................................................................................... 17 6. References ..................................................................................................................................... 18 6.1 Printed sources ............................................................................................................................ 18 6.2 Internet sources .......................................................................................................................... 19 Appendix I .............................................................................................................................................. 20 Appendix II ............................................................................................................................................. 29 Appendix III ............................................................................................................................................ 34 Appendix IV ........................................................................................................................................... 39 Appendix V ............................................................................................................................................ 41 3 4 1. Introduction 1.1 The Pachycormiformes Despite being a versatile, long-lived and successful clade of stem-teleosts, the pachycormiformes are an extremely poorly known group of bony fishes. Friedman et al. (2010) published a review and comprehensive phylogenetic data set, hypothesising a 100 million year range for the lineage and an important eco-system adaptation. Within in the pachycormiformes a wide range of different life habits are represented; hyper carnivores with enlarged fangs (e.g. Australopachycormus; Kear, 2007) and toothless filter-feeders (e.g. Bonnerichthys; Friedman, et al, 2010). Filter-feeders had and still have the ability to sometimes reach significant sizes, like the modern whale shark but the (at least) 9 meter long Leedsichthys, a filter-feeding pachycormid was possibly the largest bony fish of all time (Friedman, et al. 2010). A well-documented fossil-record supports the existence of the pachycormiformes from the lower Jurassic (the Toarcian, 183-167 Myr) to the end of the Cretaceous (65 Myr) (Friedman, et al. 2010). The group is considered to be monophyletic and can be diagnosed by some very distinctive characters: large scythe-formed pectoral fin (figure 1); a rostrodermethmoid (figure 2), which is an anterodorsal tooth-bearing bone; the absence of supraorbitals with the dermosphenotic in the dorsal part of the orbital margin; two plate-like supraorbital bones and the absence of extrascapulars (bones carrying a sensory canal) (Arratia, 2004, Kear, 2007 and Stiassny et. al. 1996). Figure 1: The scythe-formed pectoral fin of a Figure 2: The arrow is pointing at the Pachycormus bollensis rostrodermethmoid 5 1.2 Geology of Holzmaden – the Posidonia Shale Three specimens of Pachycormus bollensis, all with the same origin, have been studied for this project. They come from the famous locality of Holzmaden in the Württemberg-Baden-region, near Stuttgart, in southern Germany. The Posidonia shale (or Lower Toarcian black shale, ε) has been of considerable
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