The Lower Clayton Limestone Unit (LCLU) of the Midway Group (Paleocene) near Malvern, Arkansas, USA contains an assemblage of chondrichthyans recently exposed by excavation for highway stabilization. Chondrichthyan teeth in this assemblage belong to at least 12 taxa including: Ginglymostoma subafricanum, Carcharias cf. whitei, Carcharias sp., Odontaspis winkleri, Palaeohypotodus rutori, Palaeogaleus vincenti, Dasyatis cf. hexagonalis, Dasyatis sp., Hypolophites sp., Myliobatis sp., Rhinoptera sp., and an indeterminate chimaerid. Locally, these chondrichthyans occur within a stratigraphic section directly above the Cretaceous–Paleogene (K/Pg) boundary that also contains chondrichthyans. This occurrence is uncommon in the global fossil record and provides an opportunity to (1) assess chondrichthyan diversity across the K/Pg boundary in the Malvern region and Gulf Coastal Plain of southwestern Arkansas and (2) evaluate the timing of marginal to shallow marine chondrichthyan faunal turnover and extinction at a proximal location ≈ 1500 km from the Chicxulub, Mexico, K/Pg impact site. Observed patterns within this K/Pg stratigraphic section indicate that changes in chondrichthyan assemblages are primarily the result of sea-level cyclicity and habitat losses that occurred across several million years.

中文翻译：

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来自美国阿肯色州马尔文附近的中途岛群（古新世）下克莱顿灰岩单元的软骨鱼类，并评论了K / Pg边界

美国阿肯色州马尔文附近的中途集团（古新世）的下克莱顿石灰岩单元（LCLU）包含一群软骨鱼类，最近因开挖而被暴露以稳定公路。在此组合Chondrichthyan齿属于至少12类群包括：Ginglymostoma subafricanum，噬人鲨比照 whitei，Carcharias sp。，Odontaspis winkleri，paleohypotodus rut​​ori，paleeogaleus vincenti，Dasyatis参见。六角形，Dasyatis sp。，Hypolophites sp。，Myliobatis sp。，Rhinopterasp。和不确定的chimaerid。在本地，这些软骨鱼类发生在白垩纪-古近界（K / Pg）边界正上方的地层剖面中，该边界也包含软骨鱼类。这种情况在全球化石记录中并不常见，并提供了一个机会（1）评估阿肯色州西南部马尔文地区和墨西哥湾沿岸平原的跨K / Pg边界的软骨鱼类多样性，以及（2）评价边缘到浅海软骨鱼类的时间动物群的更新和灭绝在距墨西哥奇克卢布（Chicxulub），K / Pg撞击点约1500 km的近端位置。在该K / Pg地层剖面中观察到的模式表明，软骨鱼类组合的变化主要是几百万年来发生的海平面周期性变化和栖息地丧失的结果。