Data from: New Cretaceous lungfishes (Dipnoi, Ceratodontidae) from western North America

Ceratodontid lungfishes are generally rare, poorly-represented elements of North America’s Mesozoic ecosystems, with previously-known maximum diversity in the Late Jurassic. Herein we describe four new species of the form genus Ceratodus, from the Cretaceous of the Western Interior, considerably expanding fossil representation of post-Triassic dipnoans in North America. To model taxonomic and morphologic diversity, we adopt a four-fold system of phenetically-based species groups, named for exemplars from the Morrison Formation. Ceratodus kirklandi n. sp. (Potamoceratodus guentheri group) and C. kempae n. sp. (C. frazieri group) represent a hitherto unsampled time interval, the Valanginian. Ceratodus nirumbee n. sp. and C. molossus n. sp. extend the temporal ranges of the C. fossanovum and C. robustus groups upward to the Albian and Cenomanian, respectively. These new occurrences show that ceratodontids maintained their highest diversity from the Late Jurassic through the mid-Cretaceous (Albian–Cenomanian), an interval of some 60 Myr. The existing record suggests that some of the later (mid-Cretaceous) ceratodontids may have been tolerant of salt water; to date, there is no evidence that they aestivated. Only a few occurrences are known from horizons younger than Cenomanian; demise of ceratodontids appears to be part of a broader pattern of turnover that occurred at the Cenomanian-Turonian boundary in North America.

角齿鱼目肺鱼（Ceratodontid lungfishes）通常是北美中生代生态系统中较为稀有、化石记录匮乏的类群，此前已知的最大多样性出现于晚侏罗世。本文记述了产自北美西部内陆白垩系的4个隶属于形态属（form genus）角齿鱼属（Ceratodus）的新种，大幅扩充了北美三叠纪后肺鱼类的化石记录。为构建分类学与形态多样性模型，本文采用基于表型特征的四级物种群划分体系，以莫里逊组（Morrison Formation）的代表类群命名各组。其中，基尔坎迪角齿鱼新种（Ceratodus kirklandi n. sp.，隶属于冈瑟河角齿鱼群Potamoceratodus guentheri group）与肯帕角齿鱼新种（C. kempae n. sp.，隶属于弗雷泽角齿鱼群C. frazieri group）代表了此前未被采样的凡蓝今阶（Valanginian）地质时段；尼伦比角齿鱼新种（C. nirumbee n. sp.）与莫洛苏斯角齿鱼新种（C. molossus n. sp.）则分别将福萨诺瓦姆角齿鱼群（C. fossanovum group）与粗壮角齿鱼群（C. robustus group）的地层延限上限延伸至阿尔布阶（Albian）与森诺曼阶（Cenomanian）。这些新发现表明，角齿鱼目肺鱼的高多样性状态从晚侏罗世一直延续至白垩纪中期（阿尔布阶-森诺曼阶），时长约60百万年（60 Myr）。现有化石记录显示，部分白垩纪中期的角齿鱼目类群可能已适应咸水环境；截至目前，尚无证据表明它们存在夏眠行为。仅在少量晚于森诺曼阶的地层中发现过该类群的化石记录，角齿鱼目的灭绝似乎与北美地区森诺曼阶-土仑阶界线处发生的大规模生物更替事件密切相关。