New Age of Fishes initiated by the Cretaceous−Paleogene mass extinction

Ray-finned fishes (Actinopterygii) comprise nearly half of all modern
vertebrate diversity, and are an ecologically and numerically dominant
megafauna in most aquatic environments. Crown teleost fishes diversified
relatively recently, during the Late Cretaceous and early Paleogene,
although the exact timing and cause of their radiation and rise to
ecological dominance is poorly constrained. Here we use microfossil teeth
and shark dermal scales (ichthyoliths) preserved in deep-sea sediments to
study the changes in the pelagic fish community in the latest Cretaceous
and early Paleogene. We find that the Cretaceous−Paleogene (K/Pg)
extinction event marked a profound change in the structure of ichthyolith
communities around the globe: Whereas shark denticles outnumber ray-finned
fish teeth in Cretaceous deep-sea sediments around the world, there is a
dramatic increase in the proportion of ray-finned fish teeth to shark
denticles in the Paleocene. There is also an increase in size and
numerical abundance of ray-finned fish teeth at the boundary. These
changes are sustained through at least the first 24 million years of the
Cenozoic. This new fish community structure began at the K/Pg mass
extinction, suggesting the extinction event played an important role in
initiating the modern “age of fishes.”

辐鳍鱼（Actinopterygii）几乎占现生脊椎动物多样性的近一半，是绝大多数水生环境中生态地位突出、种群数量最为庞大的大型动物类群。冠群硬骨鱼的辐射演化发生于较近的地质时期，即白垩纪晚期与古近纪早期，但学界对其辐射演化及生态主导地位确立的确切时间与驱动机制仍知之甚少。本研究借助保存在深海沉积物中的微化石牙齿与鲨鱼真皮鳞片（ichthyoliths），探究晚白垩世至古近纪早期远洋鱼类群落的演化变迁。研究发现，白垩纪-古近纪（K/Pg）灭绝事件标志着全球范围内鱼硬组织化石群落结构发生了根本性转变：在全球白垩纪深海沉积物中，鲨鱼盾鳞的数量多于辐鳍鱼牙齿；而在古新世地层中，辐鳍鱼牙齿相较于鲨鱼盾鳞的占比出现了戏剧性的大幅提升。同时，白垩纪-古近纪界线处的辐鳍鱼牙齿在尺寸与个体数量上均出现显著增长。这些群落结构变化至少在新生代最初的2400万年中持续存在。这种全新的鱼类群落结构始于K/Pg大灭绝事件，表明该灭绝事件在催生现代"鱼类时代"的过程中发挥了关键作用。