The Pterosauria of the Early to Late Jurassic: contributions to the understanding of the origin and global radiation of the Monofenestrata

Eugénio Fernandes, Alexandra (2024): The Pterosauria of the Early to Late Jurassic: contributions to the understanding of the origin and global radiation of the Monofenestrata. Dissertation, LMU München: Fakultät für Geowissenschaften

Abstract

Pterosaurs, the first group of tetrapods to have achieved powered flight, originated in the Triassic and survived though the Jurassic and up to the Cretaceous/Paleogene extinction. However, for all of their abundance during that prolific time span, they continue to be relatively elusive, with a remarkable amount still remaining to be understood about their paleobiology and evolution, as most of the mechanisms driving their staggering diversity and morphological disparity remain unknown. Much of this is due to their inherently thin, hollow bones, which have a very low preservational potential, except under exceptional circumstances (as seen in Konservat-Lagerstätten). However, pterosaurs, representing an early offshoot of the avian lineage of archosaur, exemplify the idea that many of their special adaptations (many of which evolved during their early evolution) evolved to maximize their flight efficiency, which, in turn, led to their subsequent radiations. Most of the deductions that paleontologists have made thus far about the evolutionary history of pterosaurs have been based on specimens that largely originate in the northern hemisphere (which are much more abundant due to their longer and more intensive collection history). This has predetermined any inferences made, with the unintentional bias of excluding Gondwanan pterosaur taxa from the larger picture, and thus making it impossible to discern true biogeographic differences for Gondwana from the more dominant Laurasian faunas, or determine any role that Gondwanan pterosaurs might have played in Jurassic pterosaur evolution. More data collection from the southern hemisphere is therefore crucial in disentangling our biases, and for understanding the true role of this landmass in pterosaur evolution and pterodactyloid origins. Historically, pterosaurs were subdivided into two main groups, the “Rhamphorhynchoidea” and the Pterodactyloidea, with the pterodactyloids’ first proliferation happening during the Late Jurassic, before going on to become the most speciose group. However, recent discoveries have also shown the additional presence of several discrete lineages of closely related, non-pterodactyloid pterosaurs that were present during the Early to Middle Jurassic period, with several lines of evidence also implying a similar and concurrent origination time for the pterodactyloids, earlier than the fossil record currently marks. Part of this inference is based on the presence of an Oxfordian ctenochasmatid (a clade well nested within Pterodactyloidea), as such an earlier origin would also account for the wide diversity of pterodactyloid forms that are already known by the Late Jurassic. The aim of the current thesis is therefore to obtain a better and more comprehensive insight into several facets of the evolution and diversification of the pterosaur lineage and its surrounding paleoenvironmental implications (namely surrounding what was happening to them during the Middle-Late Jurassic), while contributing new data from the southern hemisphere as well. With this aim in mind, a new non-pterodactyloid monofenestratan from the latest Early Jurassic of Gondwana is here introduced, representing an early step in the transition between “rhamphorynchids” and pterodactyloids and identifying some potentially key morphological features in this transition, such as a vestigial ascending process of the maxilla. A special focus is then put on several additional later new species of ctenochasmatids, in a worldwide context, in an attempt to unravel their role as early pterodactyloids, investigating the timeline of their potential origins, dispersion story, and what novel characteristics made them such successful paleoecological players in surviving the Jurassic-Cretaceous transition. A new gnathosaurine taxon from Brunn, Germany, marks the earliest occurrence of this subfamily of the Ctenochasmatidae and displays novel tooth characteristics, such as a veined dental enamel. Other ctenochasmatid fossils studied herein include both an extraordinarily-sized specimen, as well as microscopic fossils from Lourinhã, Portugal, and material from a new pterosaur site from Soria, Spain, whose specialized morphological features implied a flourishing diversity at a time when biodiversity was traditionally thought to have been dwindling. Altogether, the results of these academic inquiries showcase the diversity of body sizes, rostrum shapes and dentitions shown by these filter-feeding specialists. Pterosaurs play an important role in the evolutionary history of life on earth, having been present for all of the Mesozoic, where they reached a worldwide dispersion. Better understanding their evolutionary history and their interactions with their Mesozoic environments can thus provide important insights into the evolution of terrestrial vertebrates and their environments during that time. The new data presented in this thesis provides additional evidence for this, and for the anatomical transformations that were key to the success of the Pterosauria, with new information and inferences that contribute towards unraveling several of the open questions that still linger in respect to this topic.

• Dokumententyp: Dissertationen (Dissertation, LMU München)
• Themengebiete: 500 Naturwissenschaften und Mathematik ; 500 Naturwissenschaften und Mathematik > 550 Geowissenschaften
• Fakultäten: Fakultät für Geowissenschaften
• Sprache der Hochschulschrift: Englisch
• Datum der mündlichen Prüfung: 5. Dezember 2024
• 1. Bericht­erstatter:in: Rauhut, Oliver