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Title: Taxonomy, systematics and ecomorphological diversity of Teleosauroidea (Crocodylomorpha, Thalattosuchia), and the evaluation of the genus 'Steneosaurus'
Author: Johnson, Michela Maria Angeline
ISNI:       0000 0004 8508 9138
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 2019
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Teleosauroidea represented an extraordinary group of crocodylomorphs that thrived in predominately shallow marine environments during the Mesozoic Era. While they have previously been considered as 'marine gharials' of the Jurassic, teleosauroids were in fact morphofunctionally diverse and evolved a bizarre body-plan (which included proportionally enlarged heads and femora). During the Jurassic, they attained a near-global distribution, expanded into various palaeoenvironments and became the first crocodylomorphs to grow to truly large sizes (> 7 m in length). In addition, teleosauroids were one of the first fossil crocodylomorphs to be described (1758) and named (1814), making them a historically important fossil group. Despite an increase in research over the past decade (particularly for the well-known clade Machimosaurini), the ecology and systematics of Teleosauroidea are still poorly understood and little studied. The question "What is 'Steneosaurus'?", a waste-basket genus that nearly every teleosauroid species has been placed into at some point, is a taxonomic conundrum that has hampered previous attempts to elucidate and examine teleosauroid evolutionary relationships. To rectify these issues, I examined approximately 550 specimens from 12 countries, and using this material, I created the largest and most comprehensive teleosauroid phylogenetic dataset to date; this dataset includes 502 characters and 153 crocodylomorph taxa (twenty-seven of which are teleosauroids), and was run in both TNT 1.5 and MrBayes 3.2.6. The results of both the parsimony and Bayesian analyses are consistent with one another, with two large subclades (Teleosauridae and Machimosauridae) within Teleosauroidea recovered; each one is morphologically distinct, with differing biogeographic distributions (one being Laurasian and the other Sub-Boreal European-Gondwanan) and feeding strategies. In addition, there was a significant divergence in ecomorphological characters between these subclades. While the SubAbstract Boreal subclade attained larger body-sizes (≥ 5 m) and evolved durophagy, the Laurasian subclade was more phenotypically plastic (including an east- Asian freshwater clade, a near-pelagic clade, and a heavily armoured clade). Based on my first-hand comparative anatomical and phylogenetic results, I propose major taxonomic revisions to Teleosauroidea, including: (1) redefining Teleosauridae and introducing Machimosauridae; (2) the resurrection of several historical genera; (3) erecting seven new genera; and (4) referring to the infamous genus 'Steneosaurus' as a nomen dubium. With this improved teleosauroid phylogenetic framework and updated alpha taxonomy (which allows thorough examination of their anatomical and ecological diversity), a new window has been opened on our understanding of these historically important crocodylomorphs.
Supervisor: Brusatte, Stephen ; Young, Mark ; Wood, Rachel Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: fossil crocodylomorphs ; thalattosuchians ; teleosauroids ; teleosauroid evolution ; taxonomy