Abstract

Metriorhynchoid crocodylians represent the pinnacle of marine specialization within Archosauria. Not only were
they a major component of the Middle Jurassic–Early Cretaceous marine ecosystems, but they provide further
examples that extinct crocodilians did not all resemble their modern extant relatives. Here, we use a varied toolkit
of techniques, including phylogenetic reconstruction, geometric morphometrics, diversity counts, discrete character
disparity analysis, and biomechanical finite-element analysis (FEA), to examine the macroevolutionary history of
this clade. All analyses demonstrate that this clade became more divergent, in terms of biodiversity, form, and
function, up until the Jurassic–Cretaceous boundary, after which there is no evidence for recovery or further
radiations. A clear evolutionary trend towards hypercarnivory in Dakosaurus is supported by phylogenetic
character optimization, morphometrics, and FEA, which also support specialized piscivory within Rhacheosaurus
and 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. loss
of the deltopectoral crest and retracted external nares). In addition, biomechanics, morphometrics, and characterdisparity
analyses consistently distinguish the two newly erected metriorhynchid subfamilies. This study illustrates
that together with phylogeny, quantitative assessment of diversity, form, and function help elucidate the
macroevolutionary pattern of fossil clades.