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  • Digital Humanities and Cultural Heritage
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  • DRYAD

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  • Open Access
    Authors: 
    Lee, Michael S. Y.; Yates, Adam M.;
    Publisher: Dryad Digital Repository
    Country: Netherlands
    Project: ARC | Discovery Projects - Gran... (DP160103005), ARC | Discovery Projects - Gran... (DP160103005)

    Simultaneously analysing morphological, molecular and stratigraphic data suggests a potential resolution to a major remaining inconsistency in crocodylian evolution. The ancient, long-snouted thoracosaurs have always been placed near the Indian gharial Gavialis, but their antiquity (ca 72 Ma) is highly incongruous with genomic evidence for the young age of the Gavialis lineage (ca 40 Ma). We reconcile this contradiction with an updated morphological dataset and novel analysis, and demonstrate that thoracosaurs are an ancient iteration of long-snouted stem crocodylians unrelated to modern gharials. The extensive similarities between thoracosaurs and Gavialis are shown to be an almost ‘perfect storm’ of homoplasy, combining convergent adaptions to fish-eating, as well resemblances between genuinely primitive traits (thoracosaurs) and atavisms (Gavialis). Phylogenetic methods that ignore stratigraphy (parsimony and undated Bayesian methods) are unable to tease apart these similarities and invariably unite thoracosaurs and Gavialis. However, tip-dated Bayesian approaches additionally consider the large temporal gap separating ancient (thoracosaurs) and modern (Gavialis) iterations of similar long-snouted crocodyliforms. These analyses robustly favour a phylogeny which places thoracosaurs basal to crocodylians, far removed from modern gharials, which accordingly are a very young radiation. This phylogenetic uncoupling of ancient and modern gharial-like crocs is more consistent with molecular clock divergence estimates, and also the bulk of the crocodylian fossil record (e.g. all unequivocal gharial fossils are very young). Provided that the priors and models attribute appropriate relative weights to the morphological and stratigraphic signals—an issue that requires investigation—tip-dating approaches are potentially better able to detect homoplasy and improve inferences about phylogenetic relationships, character evolution and divergence dates. DataAndResultFilesThis is a zipped file containing (1) The stratigraphic dates and sources in folder TableS1-StratAges (2) the executable PAUP, MrBayes and BEAST files for the following analyses: Morphology Only Morphology and DNA Morphology and DNA (additional sensitivity analyses) Parsimony bootstrap partition frequencies (for all partitions, not just those found in the bootstrap consensus). The BEAST files were written for BEAST 1.8.2 and will need slight edits to run on BEAST 1.8.3 onwards. We have left the files “as is” as these represent the exact files and BEAST version used.Appendix1_includingTableS2Appendix 1 CONSTRUCTION OF THE MORPHOLOGICAL MATRIXAppendix2APPENDIX 2: PHYLOGENETIC ANALYSES AND RESULTSFigsS1-9_andCaptionsFigures S1 to S9 with captions