The evolution of Metriorhynchoidea (mesoeucrocodylia, thalattosuchia): an integrated approach using geometric morphometrics, analysis of disparity, and biomechanics

Metriorhynchoid crocodylians represent the pinnacle of marine specialization within Archosauria. Not only werethey a major component of the Middle Jurassic–Early Cretaceous marine ecosystems, but they provide furtherexamples that extinct crocodilians did not all resemble their modern extant relatives. Here, we use a varied toolkitof techniques, including phylogenetic reconstruction, geometric morphometrics, diversity counts, discrete characterdisparity analysis, and biomechanical finite-element analysis (FEA), to examine the macroevolutionary history ofthis clade. All analyses demonstrate that this clade became more divergent, in terms of biodiversity, form, andfunction, up until the Jurassic–Cretaceous boundary, after which there is no evidence for recovery or furtherradiations. A clear evolutionary trend towards hypercarnivory in Dakosaurus is supported by phylogeneticcharacter optimization, morphometrics, and FEA, which also support specialized piscivory within Rhacheosaurusand Cricosaurus. Within Metriorhynchoidea, there is a consistent trend towards increasing marine specialization,with the hypermarine Cricosaurus exhibiting numerous convergences with other Mesozoic marine reptiles (e.g. lossof the deltopectoral crest and retracted external nares). In addition, biomechanics, morphometrics, and characterdisparityanalyses consistently distinguish the two newly erected metriorhynchid subfamilies. This study illustratesthat together with phylogeny, quantitative assessment of diversity, form, and function help elucidate themacroevolutionary pattern of fossil clades.