Permian and triassic tetrapods of catalonia (se europe): advances of virtual paleontology applyed to the systematics, paleobiology and paleoecology of temnospondyls
- Autores: Josep Fortuny Terricabras
- Directores de la Tesis: Àngel Galobart Lorente (dir. tes.), Carles Ferrández i Cañadell (tut. tes.)
- Lectura: En la Universitat de Barcelona ( España ) en 2011
- Idioma: español
- Tribunal Calificador de la Tesis: Alfredo Arche Miralles (presid.), Jordi Martinell Callico (secret.), J. Sébastien Steyer (voc.)
- Materias:
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- Resumen
This PhD thesis focuses on Permian and Triassic tetrapods from Catalonia (SE Europe), its systematic, and the use of virtual paleontology techniques to obtain more accurate data than previously reported about these tetrapods.
On one hand, it should be noted that few studies paid attention on the tetrapods from Permian and Triassic of Iberian Peninsula. Thus, the starting point was to review historical localities and specimens as well as to make fieldwork to recover new localities and fossils. From this point, the objective of this PhD thesis was to describe new specimens with the help of non-invasive techniques, such as CT scanners, when it was necessary.
Moreover, another important part of this PhD thesis focused on the obtention of paleobiological and paleoecological data on temnospondyls, as this group has been recovered in two different sites of the Catalonian basin. Finally, the last chapter discusses new methods to improve engineering techniques that could be useful for palaeontologists to obtain optimal results for paleobiological and paleoecological purposes.
This PhD thesis has been structured as a compendium of research articles presented as individual chapters. Some of the chapters has been already published (chapters 1, 2, 3 and 5) while others are under preparation or review of scientific journals (chapters 4 and 6). These chapters are included in four different sections, as well as an introduction to the PhD thesis.
The introduction makes a general overview of the two topics of this PhD thesis: Late Permian and Triassic vertebrate faunas and Virtual Paleontology. Both synthesize our knowledge on these two topics giving to the reader the scientific motivation, justification and the particular objectives of the research here presented.
The first section (chapter 1) shows the potential of the Iberian Permo-Triassic facies to preserve vertebrate remains, with specially emphasis on the Catalonian and Pyrenean basins. These basins have yielded unexpectedly abundant and diverse vertebrate assemblages, including actinopterygians, sarcopterygians, temnospondyls and reptiles from continental and marine environments. The re-evaluation of these localities and vertebrate diversity provide data towards an understanding of the evolutionary and palaebiogeographical history of the Permian and Triassic vertebrate Iberian faunas. Permian remains mainly correspond to footprints recovered from alluvial deposits; the osteological record is scarce in the Iberian Peninsula. Early Triassic vertebrate localities are unknown. Middle Triassic faunas are abundant and reflect the change from continental environments to a wide diversity of coastal and marine depositional environments. During the Anisian, faunas are represented by footprints and skeletal remains of amphibians (capitosaurs) and terrestrial reptiles (archosauromorphs and procolophonoids). Ichthyofauna, sauropterygians, thalattosaurs and protorosaurians are known through the late Anisian and Ladinian. Finally, Late Triassic localities representing coastal environments have also yielded marine reptiles (sauropterygians) and a diverse ichthyofauna.
The second section (chapters 2 and 3) provides new data on tetrapod footprints from the Permian of the Pyrenean basin and the systematic and phylogeny of new capitosaur genus from the Middle Triassic of the Catalonian basin.
About the Permian ichnites (chapter 2), new footprints from the Ribera d¿Urgellet area (South Pyrenees, Pyrenean basin) are reported. Two units are recognized in the region, separated by an angular unconformity. The lower unit yields tetrapod ichnites. It was dated as Upper Permian (Thuringian) by chronostratigraphic (palynology) studies, although further work is needed to confirm and precise this age. Four morphotypes are recognized, described and tentatively assigned to Chelichnus, Varanopus, Dromopus and Dimetropus. The potential trackmakers of these ichnites are caseids, captorhinomorphs, araeoscelidians and pelycosaurians. Future work should confirm the parataxonomical assignaments and the potential trackmakers.
Regarding the new capitosaur genus (chapter 3), the first capitosaur cranial remains found in the Iberian Peninsula were assigned to Parotosuchus; herein, a re-description of this material, together with information on other remains recovered from the same site, enabled to classify them as a new genus: Calmasuchus acri gen. et sp. nov. (Amphibia: Temnospondyli) from the early-to-middle Anisian (early Middle Triassic). This capitosaur had a combination of plesiomorphic and non-plesiomorphic characters, such as posterolaterally directed tabular horns, paired anterior palatal vacuities, and unique morphology of the lower jaw. By cladistic analysis, we propose a new phylogeny for the monophyletic capitosaurs. In the analysis, Capitosauria is supported by seven synapomorphies. Wetlugasaurus is the most basal member of the clade. The score of the Russian taxon Vladlenosaurus alexeyevi resulted in a clade including Odenwaldia and the latter taxa. The Madagascarian Edingerella is the sister taxon of Watsonisuchus. Finally, Calmasuchus acri, the new taxon described here, appears as a more derived form than Parotosuchus. The new genus is the sister taxon of the Cyclotosaurus-Tatrasuchus and Eryosuchus-Mastodonsaurus clades.
The third section of this PhD thesis correspond to the paleobiological and paleoecological implications that could be inferred to the group of temnospondyls (chapters 4 and 5) with the use of virtual paleontological techniques, such as Finite Element Analysis. In chapter 4, a biomechanical approach was made on the skull morphology of capitosaurs. This group of temnospondyls were one of the largest amphibians that have ever lived with a tendency to gigantism and their members displayed ecological convergence for an amphibious lifestyle. Capitosaurs are hypothesized to be `crocodilomorph¿ analogues during the Triassic period with direct bite on prey. The analysis provides new functional morphology data, using Finite Element Analysis (FEA) about the paleoeocology of the group: when feeding, capitosaurs showed a trend of concentrating the stress at the circumorbital region and cranial sutures probably play a key role in dissipating and absorbing the stress and energy resulting due to biting loads. Primitive forms were the weakest ones while the group radiated to different ecomorphotypes during all the Triassic period. Previous interpretations discussed a trend from open to closed otic notch by the (evolutionary) lateral movement of the tabular horns, but the analysis of the skull-raising system reveals that taxa exhibiting posteriorly directed tabular horns display similar results to those of closed otic notch taxa. The results suggest that various constraints besides otic notch morphology, such as the elongation of the tabular horns, snout length, skull width and position, and size of the orbits affect the functional morphology of the skull.
Regarding the chapter 5, the analysis of several clades of temnospondyls using geometric morphometrics, Finite Element Analysis (FEA), and comparative phylogenetic analysis are discussed. Temnospondyls were a successful group of early tetrapods that lived during the Paleozoic and Mesozoic periods. Different ecomorphotypes were present (terrestrial, amphibious, and fully aquatic) with a wide range of lifestyles. Some temnospondyli clades were ¿crocodilomorph¿ feeding analogues. The skull analysis reveals a concordance between form and feeding function, in amphibious and fully aquatic feeders. The form of terrestrial feeders could be consequence of adaptative or phylogenetical constraints. Basal temnospondyls, as edopoids, were able to leave the water and feed on land. Eryopids continued as terrestrial feeders, although some members showed a shift to increased aquatic feeding. The aquatic environment was especially occupied by archegosaurs during the Permian. After the Permo-Triassic extinction, trematosaurs and capitosaurs returned to the aquatic environment and their members were amphibious and fully aquatic feeders until their disappearance.
Finally, the chapter 6, focuses on computational methods to improve biomechanical results and pays specially attention to the generation of meshes used to make engineering analysis; in computational mechanics the theory says that smaller the size of the mesh, the more accurate the result will be. Although computers can mostly solve the large mathematical models created by automatically generated fine meshes, mesh generation for a Finite Element Analysis (FEA) should be done with a consistent criterion and cannot always be done automatically.
