title: A large aberrant stem ichthyosauriform indicating early rise and demise of ichthyosauromorphs in the wake of the end-Permian extinction.
abstract: Contrary to the fast radiation of most metazoans after the end-Permian mass extinction, it is believed that early marine reptiles evolved slowly during the same time interval. However, emerging discoveries of Early Triassic marine reptiles are questioning this traditional view. Here we present an aberrant basal ichthyosauriform with a hitherto unknown body design that suggests a fast radiation of early marine reptiles. The new species is larger than coeval marine reptiles and has an extremely small head and a long tail without a fluke. Its heavily-built body bears flattened and overlapping gastral elements reminiscent of hupehsuchians. A phylogenetic analysis places the new species at the base of ichthyosauriforms, as the sister taxon of Cartorhynchus with which it shares a short snout with rostrally extended nasals. It now appears that ichthyosauriforms evolved rapidly within the first one million years of their evolution, in the Spathian (Early Triassic), and their true diversity has yet to be fully uncovered. Early ichthyosauromorphs quickly became extinct near the Early-Middle Triassic boundary, during the last large environmental perturbation after the end-Permian extinction involving redox fluctuations, sea level changes and volcanism. Marine reptile faunas shifted from ichthyosauromorph-dominated to sauropterygian-dominated composition after the perturbation.
authors.affiliation: Laboratory of Orogenic Belt and Crustal Evolution, Ministry of Education; Department of Geology and Geological Museum, Peking University, Yiheyuan Street. 5, Beijing 100871, People's Republic of China.
authors.forename: Da-Yong
authors.initials: DY
authors.lastname: Jiang
authors.affiliation: Department of Earth and Planetary Sciences, University of California, Davis, One Shields Avenue, Davis, California 95616, United States of America.
authors.forename: Ryosuke
authors.initials: R
authors.lastname: Motani
authors.affiliation: Department of Research, Anhui Geological Museum, Jiahe Road 999, Hefei, Anhui 230031, People's Republic of China.
authors.forename: Jian-Dong
authors.initials: JD
authors.lastname: Huang
authors.affiliation: Dipartimento di Scienze della Terra, Università degli Studi di Milano, Via Mangiagalli 34-20133 Milano, Italy.
authors.forename: Andrea
authors.initials: A
authors.lastname: Tintori
authors.affiliation: Department of Research, Anhui Geological Museum, Jiahe Road 999, Hefei, Anhui 230031, People's Republic of China.
authors.forename: Yuan-Chao
authors.initials: YC
authors.lastname: Hu
authors.affiliation: Center of Integrative Research, The Field Museum, Chicago, IL 60605-2496, United States of America.
authors.forename: Olivier
authors.initials: O
authors.lastname: Rieppel
authors.affiliation: National Museums Scotland, Chambers Street, Edinburgh EH1 1JF, United Kingdom.
authors.forename: Nicholas C
authors.initials: NC
authors.lastname: Fraser
authors.affiliation: Key Laboratory of Economic Stratigraphy and Palaeogeography, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, 39 East Beijing Road, Nanjing 210008, People's Republic of China.
authors.forename: Cheng
authors.initials: C
authors.lastname: Ji
authors.affiliation: Smithsonian Institution, National Museum of Natural History, Washington, DC 20560-0121, United States of America.
authors.forename: Neil P
authors.initials: NP
authors.lastname: Kelley
authors.affiliation: Laboratory of Orogenic Belt and Crustal Evolution, Ministry of Education; Department of Geology and Geological Museum, Peking University, Yiheyuan Street. 5, Beijing 100871, People's Republic of China.
authors.forename: Wan-Lu
authors.initials: WL
authors.lastname: Fu
authors.affiliation: Department of Research, Anhui Geological Museum, Jiahe Road 999, Hefei, Anhui 230031, People's Republic of China.
authors.forename: Rong
authors.initials: R
authors.lastname: Zhang
mesh_terms: D000818:Animals; D059001:Aquatic Organisms / Q000145:classification*; D005075:Biological Evolution; D005580:Fossils; D010802:Phylogeny; D012104:Reptiles / Q000033:anatomy & histology* / Q000145:classification*