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-白垩纪过渡时期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，但鲜有古生物学研究聚焦于此，以及探究驱动该时期动物群更替的潜在气候与生物因子。因此，绝大多数类群的演化模式仍未得到充分阐明。我们依托一套全新的大型形态学数据集，对海洋四足类群蛇颈龙目（Plesiosauria）的类群多样性与形态差异度（形态多样性格局）展开分析，并将该类群的演化模式与其他生物类群进行对比。尽管此前有假说认为共有7支蛇颈龙类类群跨越了侏罗纪-白垩纪界线，但我们得到的最简约拓扑结构显示，实际仅存在3支。此次研究稳健恢复出一个包含绝大多数白垩纪蛇颈龙超科类群的新演化支（Xenopsaria，新演化支），这一结果对本研究结论起到关键支撑作用。侏罗纪-白垩纪界线时段内蛇颈龙类发生了显著的类群更替：上龙科与隐锁龙科的多样性与形态差异度大幅缩减，随后Xenopsaria演化支在早白垩世发生辐射演化。此次类群更替的潜在物理驱动因子包括影响海洋生产力与多样性的气候波动：晚侏罗世全球气候以广泛分布的季风系统为特征，且有更多营养盐输入至正在张开的大西洋-特提斯洋，进而引发水体富营养化，形成生产力旺盛但分类群极度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，导致海洋环境转为贫营养化，使得放射虫、钙质超微浮游生物乃至菊石类的分类群多样性显著提升。然而，对鱼龙类与海洋鳄形类等其他海洋四足类群的研究发现其灭绝模式与蛇颈龙类并不一致，这表明在侏罗纪-白垩纪界线时段的动物群更替驱动机制中，类群特异性因子可能比全局性外在因子发挥了更为关键的作用。