Fossil vertebrates from a unique marine bonebed of the Upper Cretaceous Niobrara Chalk, western Kansas, U.S.A.: new insights into the Niobrara vertebrate paleoecology
Date of Award
Master of Science (MS)
Kenshu Shimada, PhD
The Smoky Hill Chalk Member of the Niobrara Chalk is a sedimentary deposit formed in the Western Interior Seaway of North America during the Late Cretaceous. In this study, I examined a unique fossiliferous bonebed from an uncertain horizon within the Smoky Hill Chalk in Gove County, Kansas, U.S.A. Over 40,450 taxonomically identifiable specimens were collected, where they consisted of at least four chondrichthyans, 24 osteichthyans, and two tetrapods, including taxa such as Nanocorax, Squalicorax, Rhinobatos, pycnodontids, Lepisosteidae, Protosphyraena, Pachyrhizodus, ichthyodectiforms, plethodids, Albulidae, Apateodus, Ichthyotringidae(?), cf. Stratodus, Cimolichthys, Enchodus, Acanthomorpha, Platecarpus, and Hesperornithiformes. The diversity of these vertebrates suggests the presence of a very complex ecosystem when the bonebed formed, which is determined to be of the latest Santonian in age possibly about 84.0 ± 0.3 Ma on the basis of biostratigraphic, geographic, and geologic evidence. Based on published literature and this new study, at least 117 vertebrate taxa are now known from the Smoky Hill Chalk of Kansas, comprising 18 chondrichthyans, 63 osteichthyans, and 36 tetrapods. Comparisons of faunal data from the bonebed with databases on vertebrate fossils from the Niobrara Chalk of Kansas in seven major museum collections indicate that the commonness of taxa by number of specimens in the bonebed and that in the museums are markedly different. The Niobrara fossil record based on museum collections appears to be biased towards large reptilian remains compared to osteichthyan fossils. In particular, this study indicates that Enchodus spp. were especially common when the bonebed formed. A major corollary from this study is that a more accurate reconstruction of the paleoecology of the Western Interior Seaway requires the need for more analyses on smaller vertebrate taxa.
Allen, Jonathan, "Fossil vertebrates from a unique marine bonebed of the Upper Cretaceous Niobrara Chalk, western Kansas, U.S.A.: new insights into the Niobrara vertebrate paleoecology" (2021). College of Science and Health Theses and Dissertations. 447.