Ecomorphological diversifications of Mesozoic marine reptiles: the roles of ecological opportunity and extinction

—Mesozoic marine ecosystems were dominated by several clades of reptiles, including sauropterygians, ichthyosaurs, crocodylomorphs, turtles, and mosasaurs, that repeatedly invaded ocean ecosystems. Previous research has shown that marine reptiles achieved great taxonomic diversity in the Middle Triassic, as they broadly diversified into many feeding modes in the aftermath of the Permo-Triassic mass extinction, but it is not known whether this initial phase of evolution was exceptional in the context of the entire Mesozoic. Here, we use a broad array of disparity, morphospace, and comparative phylogenetic analyses to test this. Metrics of ecomorphology, including functional disparity in the jaws and dentition and skull-size diversity, show that theMiddle to early Late Triassic represented a time of pronounced phenotypic diversification in marine reptile evolution. Following the Late Triassic extinctions, diversity recovered, but disparity did not, and it took over 100Myr for comparable variation to recover in the Campanian and Maastrichtian. Jurassicmarine reptiles generally failed to radiate into vacated functional roles. The signatures of adaptive radiation are not seen in all marine reptile groups. Clades that diversified during the Triassic biotic recovery, the sauropterygians and ichthyosauromorphs, do show early diversifications, early high disparity, and early burst, while less support for these models is found in thalattosuchian crocodylomorphs andmosasaurs. Overall, the Triassic represented a special interval inmarine reptile evolution, as a number of groups radiated into new adaptive zones. Thomas L. Stubbs and Michael J. Benton. School of Earth Sciences, University of Bristol, Bristol BS8 1RJ, U.K. E-mail: [email protected] Accepted: 14 March 2016 Published online: 17 May 2016 Supplemental materials deposited at Dryad: doi:10.5061/dryad.5890r