Data from: Faunal turnover of marine tetrapods during the Jurassic–Cretaceous transition

Marine and terrestrial animals show a mosaic of lineage extinctions and diversifications during the Jurassic–Cretaceous transition. However, despite its potential importance in shaping animal evolution, few palaeontological studies have focussed on this interval and the possible climate and biotic drivers of its faunal turnover. In consequence evolutionary patterns in most groups are poorly understood. We use a new, large morphological dataset to examine patterns of lineage diversity and disparity (variety of form) in the marine tetrapod clade Plesiosauria, and compare these patterns with those of other organisms. Although seven plesiosaurian lineages have been hypothesised as crossing the Jurassic–Cretaceous boundary, our most parsimonious topology suggests the number was only three. The robust recovery of a novel group including most Cretaceous plesiosauroids (Xenopsaria, new clade) is instrumental in this result. Substantial plesiosaurian turnover occurred during the Jurassic–Cretaceous boundary interval, including the loss of substantial pliosaurid, and cryptoclidid diversity and disparity, followed by the radiation of Xenopsaria during the Early Cretaceous. Possible physical drivers of this turnover include climatic fluctuations that influenced oceanic productivity and diversity: Late Jurassic climates were characterised by widespread global monsoonal conditions and increased nutrient flux into the opening Atlantic-Tethys, resulting in eutrophication and a highly productive, but taxonomically depauperate, plankton. Latest Jurassic and Early Cretaceous climates were more arid, resulting in oligotrophic ocean conditions and high taxonomic diversity of radiolarians, calcareous nannoplankton and possibly ammonoids. However, the observation of discordant extinction patterns in other marine tetrapod groups such as ichthyosaurs and marine crocodylomorphs suggests that clade-specific, factors may be more important than overarching extrinsic factors in driving faunal turnover during the Jurassic–Cretaceous boundary interval.

海洋与陆生动物在侏罗纪-白垩纪之交呈现出类群灭绝与辐射演化交织的镶嵌式演化格局。尽管该时段对动物演化的塑造具有潜在重要意义，但古生物学研究中极少聚焦于此时段，以及该时期动物群更替可能的气候与生物驱动因素。因此，绝大多数类群的演化模式至今仍鲜为人知。本研究依托全新的大型形态学数据集，探究海洋四足类群蛇颈龙目（Plesiosauria）的类群多样性与形态差异度（即形态多样性），并将这些模式与其他生物类群进行对比。此前有假说认为共有7个蛇颈龙类支系跨越了侏罗纪-白垩纪界线，但本研究最简约的系统发育拓扑结构显示，这一数量仅为3个。包含绝大多数白垩纪蛇颈龙超科类群的全新支系（Xenopsaria，新支系）的稳健恢复，是得出该结论的关键所在。侏罗纪-白垩纪界线时段内发生了显著的蛇颈龙类群更替：包括上龙科（Pliosauridae）与隐锁龙科（Cryptoclididae）的多样性及形态差异度大幅丧失，随后Xenopsaria支系在早白垩世发生辐射演化。该更替事件的潜在物理驱动因素包括影响海洋生产力与多样性的气候波动：晚侏罗世气候以全球广泛分布的季风条件为特征，且向正在扩张的大西洋-特提斯洋输入的营养物质通量增加，由此引发富营养化，形成生产力极高但分类学多样性匮乏的浮游生物群落。晚侏罗世末期至早白垩世气候更为干旱，形成寡营养海洋环境，放射虫（radiolarians）、钙质超微浮游生物（calcareous nannoplankton）以及可能的菊石类（ammonoids）的分类学多样性显著升高。然而，在鱼龙目（ichthyosaurs）与海洋鳄形类（marine crocodylomorphs）等其他海洋四足类群中观察到的灭绝模式并不一致，表明在侏罗纪-白垩纪界线时段的动物群更替驱动因素中，支系特异性因素可能比全局性外在因素更为重要。