Taxonomy, phylogeny and palaeoecology of the plesiosauroids (Sauropterygia, Reptilia) from the Posidonia shale (Toarcian, lower Jurassic) of Holzmaden, south west Germany [Elektronische Ressource] / vorgelegt von Franziska Großmann

Informations

• Publié par: eberhard_karls_universitat_tubingen
• Publié le: 01 janvier 2006
• Nombre de lectures: 14
• Langue: English
• Poids de l'ouvrage: 19 Mo

Extrait

Taxonomy, phylogeny and palaeoecology of the
plesiosauroids (Sauropterygia, Reptilia) from the Posidonia
shale (Toarcian, Lower Jurassic) of Holzmaden, south west
Germany

Dissertation
zurErlangungdesGradeseinesDoktorsderNaturwissenschaften
derGeowissenschaftlichenFakultät
derEberhard-Karls-UniversitätTübingen
vorgelegtvon
FranziskaGroßmann
ausBochum
2006
TagdermündlichenPrüfung:11.12.2006
Dekan:Prof.Dr.P.Grathwohl
1.Berichterstatter:Prof.Dr.W.E.Reif
2.Berichterstatter:Prof.Dr.J.H.NebelsickContents
page
Zusammenfassung i
Abstract iii
Chapter1:IntroductIon 1
Historyof plesiosaurresearch 2
ThePosidoniashale 3
TheplesiosaursfromthePosidoniashale 8
Aimsof thethesis 10
Chapter2:MaterIal and classIfIcatIon 13
Introduction 13
Descriptionof specimens 13
Classifcation 38
Results 40
Chapter3:systeMatIc palaeontology 43
Seeleyosaurus guilelmiimperatoris 43
Hydrorion brachypterygius 49
Comparison 54
Chapter4:phylogenetIc analysIs 59
Introductionandmethods 59
Resultsanddiscussion 60
Defnition of characters 63
Chapter5:functIonal Morphology 71
Functionalmorphologyof theskull 71
Introduction and methods 71
Description 72
Functional analysis 76
Results 79
Discussion 82
Functionalmorphologyof thelimbs 84
Introduction 84
Functional analysis 88
Chapter6:palaeoecology 91
Introduction 91
Dietandfeeding 91
Habitat 97
Palaeobiogeography 100
Acknowledgements 105
References 107
Appendix 121
A:Listof abbreviations 121
B:Measurementsof studiedspecimens 122
C:Valuesusedinthefunctionalanalysisof thecranialmusculature 125
D: Table of plesiosaur fndings from the Posidonia shale 127Zusammenfassung
De Plesosauroden aus dem Posdonenschefer (Toarcum, Unterer Jura) von Holzmaden
(Baden-Württemberg) wurden detallert studert, hre taxonomsche und phylogenetsche Poston
analysert und revdert, und hre Palökologe untersucht.
Dafür wurden 10 vollständge Skelette detallert aufgenommen, ver beschrebene und
sechs unbeschriebene. Unter den Stücken befnden sich die Holotypen der drei Arten Plesiosaurus
guilelmiimperatoris Dames, 1895, Plesiosaurus brachypterygius v. Huene, 1923 und Plesiopterys wildii O‘Keefe
2004, sowie ein weiteres beschriebenes Stück der Art P. guilelmiimperatoris (fraas 1910). Anhand von
morphologischen Merkmalen und einer statistischen Analyse wurden die unbeschriebenen Stücke,
sofern möglich, vorhandenen Arten zugeordnet.
P. brachypterygius und P. guilelmiimperatoris unterscheiden sich deutlich von der Typus Art der Gattung
Plesiosaurus, P. dolichodeirus, und auch untereinander, und beide Arten wurden eigenen Gattungen
zugeordnet. Für P. guilelmiimperatoris wurde die Gattung Seeleyosaurus WHite, 1940 weder belebt,
während für P. brachypterygius die neue Gattung Hydrorion aufgestellt wurde. Plesiopterys wildii stellt en
jüngeres taxonomsches Synonym von P. guilelmiimperatoris dar.
Eine phylogenetische Analyse zeigte, daß beide deutschen Gattungen zu der Familie der
Elasmosaurden gehören. Seeleyosaurus guilelmiimperatoris ähnelt stark der englischen Gattung
Muraenosaurus, während Hydrorion brachypterygius mit den Gattungen Microcleidus und Occitanosaurus ene
monophyletische Gruppe bildet, welche die Schwestergruppe der kretazischen Elasmosaurier ist.
Die Schädelmuskulatur beider Gattungen wurde rekonstruiert und analysiert. Dabei stellte sich
heraus, daß Hydrorion höhere Beißkräfte ausüben konnte als Seeleyosaurus, letzterer konnte dagegen
sein Maul schneller schließen. Der Vergleich der Flossen zeigte, daß Hydrorion en sehr wendger
Schwmmer war, während Seeleyosaurus eher für ausdauerndes und schnelles Schwimmen angepaßt
war. Diese Eigenschaften der beiden Gattungen wurden mit dem möglichen Beutespektrum aus
dem Posidonienschiefer verglichen. Vermutlich spezialisierte sich Hydrorion auf den Schwarmfsch
Leptolepis, während Seeleyosaurus eher Tintenfsche jagte.
Der Vergleich von Plesiosauriern aus dem Lias von Europa zeigte, daß eine deutliche
paläobiogeographische Zonierung auf Art- und Gattungsniveau bestand.
Abstract
The plesiosauroids from the Posidonia shale (Toarcian, Lower Jurassic) of Holzmaden (south
west Germany) were examined in detail, their taxonomic and phylogenetic position was analysed and
revsed and ther palaeoecology studed.
Ten complete specmens were studed, ncludng the type specmens of Plesiosaurus guilelmiimperatoris
Dames, 1895, Plesiosaurus brachypterygius v. Huene, 1923 and Plesiopterys wildii O’Keefe, 2004, as well
as a descrbed specmen of P. guilelmiimperatoris (fraas 1910). Where possble, the sx undescrbed
specmens were assgned to one of the exstng speces, on the bass of morphologcal characters and
a statstcal analyss.
P. brachypterygius and P. guilelmiimperatoris differ suffciently from the type species of the genus
Plesiosaurus, Plesiosaurus dolichodeirus, and from each other to be assgned to separate genera. The genus
Seeleyosaurus WHite, 1940 was re-establshed for P. guilelmiimperatoris, and the new genus Hydrorion
was ntroduced for P. brachypterygius. Plesiopterys wildii turned out to be a junor synonym of P.
guilelmiimperatoris.
A phylogenetic analysis placed both German genera within the family Elasmosauridae. Seeleyosaurus
guilelmiimperatoris resembles strongly the Englsh genus Muraenosaurus. Hydrorion brachypterygius forms a
monophyletc group wth Microcleidus and Occitanosaurus, whch s the sster taxon to the cretaceous
elasmosaurs.
The cranial musculature of both German taxa was reconstructed and analysed. It could be
shown that Hydrorion was able to exert hgher btng forces than Seeleyosaurus, whereas the latter could
close his jaws faster. A comparison of the fipper morphology indicated that Hydrorion was a hghly
manoeuvrable swimmer. In contrast to this, Seeleyosaurus was better adapted for stamna and speed.
These qualtes were compared to the possble prey from the Posdona shale. Hydrorion probably
specialised on the swarm-fsh Leptolepis, whereas Seeleyosaurus s more lkely to have caught coleods
(squid and cuttlefsh).
The comparison of Liassic plesiosaurs from Europe showed that palaeobiogeographic zonation
was present at speces and genus level.
Chapter 1
INTRODUCTION
Despite having been studied for 185 years, plesiosaurs remain an enigmatic group. With their four
fipper-like limbs and their elongated neck, they have no modern analogue that would contribute to
the understanding of their locomotion, diet and ecological preferences.
Plesiosaurs belong to the Sauropterygia, an extinct group of marine reptiles that lived from the
Triassic until the end of the Cretaceous. The plesiosaurs, which appear in the uppermost Triassic
(Taylor & CruiCkshank 1993a, sTorrs 1994a, sTorrs & Taylor 1996), are the most derived members
of this group (Fig. 1.1), and show a high degree of adaptation to the marine environment. Their four
limbs have the form of hydrofoil-shaped fippers, and are used for locomotion. The trunk and tail
are relatively short and the neck is elongated. The plesiosaurs are divided into two groups: (1) the
pliosauroids, with relatively short necks and large skulls (Fig. 1.2), and (2) the plesiosauroids, with small
skulls and elongated necks (Fig. 1.3). In some Cretaceous members of the family Elasmosauridae the
neck can be twice as long as the trunk.
All plesiosaurs were predators, feeding mainly on fsh and cephalopods. Due to their small head,
the prey of plesiosauroids was restricted to small forms. In contrast to this, pliosauroids also attacked
Fig. 1.1: Phylogeny of the Sauropterygia (modifed after rieppel 1999).
1Chapter 1
Fig. 1.2: Liopleurodon ferox, a typical pliosauroid from the Callovian (Lower Jurassic) of England. (Artwork courtesy of A.
S. sMiTh.)
prey larger than themselves, including other marine reptiles. With their strong jaws and sharp teeth
they were able to dismember their prey after the kill.
The four limbs were used for under-water fight, a method of locomotion used by turtles, penguins
and otariids. The limbs have a cross-section similar to that of a bird wing or an aeroplane wing, and
like these they work by creating lift by inducing differential velocities of the surrounding medium
above and below the wing (Fig. 1.4). Tilting the wing produces a forward drag.
History of plesiosaur research
Plesiosaurs were amongst the frst vertebrate fossils studied at the beginning of palaeontology. de
la BeChe & ConyBeare (1821) described some vertebrae, naming them “Plesiosaurus”. Descriptions
of other, more complete specimens followed soon (ConyBeare 1822 & 1824, hawkins 1834 & 1840,
owen 1838), and plesiosaurs were also discovered in America (harlan 1824 & 1825), Germany (v.
Meyer 1841) and New Zealand (huTTon 1844). These early descriptions are still remarkable for
their quality, both in the detailed descriptions and in the beautiful and highly accurate illustrations.
Although much work has been done since then, concerning the taxonomy (for example: welles 1952,
Tarlo 1960, Brown, d. s. 1981 & 1983, CarpenTer 1996 & 1999, sTorrs 1997, o’keefe 2001a,