ABSTRACT We report on new collections of cephalopods (ammonites and nautilids) from the Cretaceous-Paleogene (K-Pg) successions of the Corsicana and Kincaid formations exposed along the Brazos River in Falls County, Texas. An abundant fauna of eight species comprising four genera of ammonites is described from the Corsicana Formation, including Discoscaphites mullinaxorum n. sp. The presence of abundant aptychi (probably lower jaws) of Discoscaphites and Eubaculites, as well as juvenile specimens, indicates a living population that experienced little postmortem drift. The lytoceratid genus Gaudryceras is also reported for the first time from the Brazos River area. Presence of the index taxon Discoscaphites iris (Conrad, 1858) indicates that the fauna belongs to the D. iris Range Zone, the highest ammonite range zone in North America. Correlation with new and existing microfossil data indicates that the fauna represents the uppermost Maastrichtian, and comparison with published records further suggests that this is the most diverse D. iris Zone fauna yet reported from the Gulf and Atlantic Coastal Plains of North America. Three ammonite genera are recorded from the basal units of the K-Pg event deposit at Brazos, which likely represents deposition in the immediate aftermath of the Chicxulub impact event. A single specimen of the nautilid Eutrephoceras is reported from the Danian Kincaid Formation, less than 300 kyr after the K-Pg boundary. These data provide new information on the differing fate of these cephalopod groups during the K-Pg mass extinction and add to the picture of diverse and abundant Maastrichtian ammonite faunas prior to the Chicxulub impact event.

中文翻译：

---

德克萨斯州布拉索斯河白垩纪-古近纪 (K-Pg) 边界区间的头足类动物和菊石的灭绝

摘要 我们报告了来自德克萨斯州福尔斯县布拉索斯河沿岸的 Corsicana 和 Kincaid 地层的白垩纪-古近纪 (K-Pg) 序列的头足类动物（菊石和鹦鹉螺）的新收藏。科西嘉组描述了包含 4 个菊石属的 8 个物种的丰富动物群，包括 Discoscaphites mullinaxorum n。sp. 存在大量 Discoscaphites 和 Eubaculites 的 aptychi（可能是下颌），以及幼年标本，表明活着的种群几乎没有死后漂移。lytoceratid 属 Gaudryceras 也是首次从布拉索斯河地区报道。指数分类群 Discoscaphites iris (Conrad, 1858) 的存在表明该动物群属于 D. iris Range Zone，这是北美最高的菊石分布区。与新的和现有的微化石数据的相关性表明，该动物群代表了最上层的马斯特里赫特，与已发表的记录的比较进一步表明，这是北美海湾和大西洋沿岸平原报告的最多样化的 D. iris 区动物群。在布拉索斯的 K-Pg 事件沉积物的基础单元中记录了三个菊石属，这可能代表了希克苏鲁伯撞击事件之后立即发生的沉积。据报道，在距离 K-Pg 边界不到 300 kyr 的 Danian Kincaid 组中发现了一个鹦鹉螺类 Eutrephoceras 的标本。这些数据提供了关于 K-Pg 大灭绝期间这些头足类群的不同命运的新信息，并增加了希克苏鲁伯撞击事件之前多样化和丰富的马斯特里赫特菊石动物群的图景。