New paddlefishes (Acipenseriformes, Polyodontidae) from the Late Cretaceous Tanis Site of the Hell Creek Formation in North Dakota, USA

The recently discovered mass mortality of fishes from the Tanis Site in the North Dakota portion of the Late Cretaceous Hell Creek Formation contains many well-preserved, three-dimensional skeletons. Among these are representatives of two acipenseriform families, Acipenseridae (sturgeons) and Polyodontidae (paddlefishes). This paper describes two new monotypic polyodontid genera, expanding our knowledge of polyodontid diversity. The first of the new species described here is +Parapsephurus willybemisi n. gen. n. sp. It is distinguished from all other known species by having a combination of posteriorly elongate parietals, the middle fenestra longitudinalis bordered medially by the parietal and frontal and laterally by the dermopterotic, slender and numerous dorsal caudal fulcra, an elongate hyomandibula that is not hourglass shaped, and gill rakers that are short and widely spaced. The second polyodontid species described here is dagger Pugiopsephurus inundatus n. gen. n. sp. It is diagnosed by a combination of having stellate bones that are exceptionally poorly developed or absent and having a dermopalatine with a medial expansion and lacking an ectopterygoid process. The two species of paddlefishes described in this paper add to the morphological and taxonomic diversity of Polyodontidae. The presence of these taxa within the Hell Creek Formation hints at substantial diversity of polyodontids at this stage of their evolutionary history.

Automated summary

The recent discovery of mass fish mortality in the Tanis Site in the Late Cretaceous Hell Creek Formation in North Dakota has yielded well-preserved, three-dimensional fish skeletons. Two new species of paddlefishes, belonging to the families Acipenseridae and Polyodontidae, are described in this paper, expanding our knowledge of paddlefish diversity. These new species display unique characteristics, such as elongated parietals, slender dorsal caudal fulcra, and poorly developed stellate bones, adding to the morphological and taxonomic diversity of Polyodontidae. The presence of these species in the Hell Creek Formation suggests a significant diversity of paddlefishes during this stage of their evolutionary history.