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Title: A multi-disciplinary approach to the analysis of crocodylian phylogeny, diversity and biogeographic history in Deep Time
Author: Groh, Selina
ISNI:       0000 0004 7660 6586
Awarding Body: UCL (University College London)
Current Institution: University College London (University of London)
Date of Award: 2019
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Crocodylomorpha are one of the oldest extant clades on the planet, having originated over 200 million years ago in the Triassic. Their large fossil diversity stands in contrast to only 23 living species, providing a rich source for evolutionary study. In addition, they illustrate the influence of homoplasy on phylogenetic reconstruction: an elongated snout form ('longirostry') arose multiple times throughout their history, causing erroneous clade clustering inconsistent with the stratigraphic record in phylogenetic analyses. For this thesis, the largest dataset to date was assembled for Neosuchia, a crocodylomorph clade consisting of all extant and several extinct families. 569 characters (82 continuous and 487 discrete) were scored for 106 taxa and analysed using Bayesian and parsimony methods (with and without Extended Implied Weighting (EIW)). The resulting phylogenies were evaluated using stratigraphic congruence, dated with four different methods (cal3, FBD, sGLA and Extended Hedman), and analysed for their biogeographical patterns. The results show that using both EIW and continuous characters successfully resolves the issue of homoplasy, producing the most stratigraphically congruent trees. They confirm the position of Diplocynodontinae, Goniopholididae and Tethysuchia as non-eusuchian neosuchians and resolve the three major eusuchian superfamilies, Crocodyloidea, Gavialoidea and Alligatoroidea, although Alligatorinae emerge as non-monophyletic. Character tracing reveals that similar modifications in the anterior of the skull underpin the evolution of longirostry in all clades, coupled with more clade-specific modifications of the posterior skull. Divergence age estimation places the emergence of Neosuchia in the late Triassic, confirming that all three major eusuchian clades were present before the K/Pg-boundary. Cal3 and FBD emerged as the most accurate divergence age estimation methods. Biogeographical analyses showed that neosuchian biogeography is complicated, but most clades emerged on the Laurasian continents, with a definite European origin for Alligatoroidea. Founder event speciation and transoceanic dispersal played an important role in neosuchian evolution.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available