Abstract Temporal changes in the diversity of euselachians (e.g., sharks and rays) across the Cretaceous-Paleogene (K-Pg) boundary are not well understood, particularly from freshwater ecosystems. Here, we quantitatively analyze euselachian diversity during the last ca. 2 Ma of the Cretaceous using 1518 teeth from 40 vertebrate microfossil localities within the nonmarine facies of the Hell Creek Formation, northeastern Montana, USA. We identify 10 euselachians including one hybodont, five orectolobiforms, one lamniform, one sclerorhynchiform, and two rajiforms. Among these, two are novel and described herein. Diversity metrics reveal an increase in species richness and heterogeneity from the lower to middle portions of the Hell Creek Formation. Thereafter, diversity remained elevated and stable with no turnover until ~5 m below the K-Pg boundary. Above this horizon, including the last ~50 kyr of the Cretaceous, raw species richnesses dropped precipitously, and all euselachians (except possibly Myledaphus) went locally extinct across the boundary. Preceding this drop in richness, changes in euselachian community structure occurred, including steady declines in the relative abundances of M. pustulosus. These patterns do not support regression of the Western Interior Seaway as the single proximal cause of euselachian extinctions across the K-Pg boundary. Rather, euselachian local extinctions likely were the result of the multiple environmental perturbations occurring just before (volcanism, climate change) and at the K-Pg boundary (bolide impact). This high-resolution temporal pattern of euselachian diversity adds to those from other local taxa (e.g., mammals, lissamphibians) to present a more complex view of the K-Pg mass extinction of the continental biota.

中文翻译：

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通过美国蒙大拿州加菲尔德县白垩纪地狱溪组最上层的 Euselachian 多样性，对淡水环境中白垩纪-古近纪大灭绝的影响

摘要 跨白垩纪-古近纪 (K-Pg) 边界的真鲨类（例如鲨鱼和鳐鱼）多样性的时间变化尚不清楚，尤其是淡水生态系统。在这里，我们定量分析了最后一个 ca 期间的 euselachian 多样性。2 Ma 使用来自美国蒙大拿州东北部地狱溪组非海相内 40 个脊椎动物微化石位置的 1518 颗牙齿。我们确定了 10 种euselachians，包括一种舌齿动物、5 种 orectolobiforms、一种 lamniform、一种 sclerorhynchiform 和两种 rajiforms。其中，有两个是新颖的并在此描述。多样性指标显示，从地狱溪组的下部到中部，物种丰富度和异质性有所增加。此后，多样性保持升高和稳定，直到 K-Pg 边界以下约 5 m 才发生周转。在这个地平线之上，包括白垩纪的最后约 50 kyr，原始物种丰富度急剧下降，所有真鲨类（可能除了 Myledaphus）在边界上局部灭绝。在丰富度下降之前，euselachian 群落结构发生了变化，包括 M. pustulosus 的相对丰度稳步下降。这些模式不支持西部内陆海道的回归作为跨 K-Pg 边界的真鲨类灭绝的单一近端原因。相反，euselachian 局部灭绝可能是之前（火山作用、气候变化）和 K-Pg 边界（火流星撞击）发生的多重环境扰动的结果。这种真鲨目多样性的高分辨率时间模式增加了来自其他地方分类群（例如，哺乳动物、