The dinosaurian fauna of the Niobrara Chalk Formation constitutes the best known assemblage from the middle Santonian-early Campanian interval of the Late Cretaceous of North America. The fauna consists of both hadrosaurid ornithopods and nodosaurid ankylosaurs. The nodosaurid specimens from the Smoky Hill Chalk Member of the Niobrara Chalk Formation include the holotype of Hierosaurus sternbergii (here regarded as nomen dubium), material of " Hierosaurus" coleii (herein designated the type species of the new genus Niobrarasaurus) and two specimens that may belong to N. coleii, but are better interpreted as Nodosauridae incertae sedis. Claosaurus agilis, the sole hadrosaurid from the Niobrara Chalk Formation, constitutes a poorly known, but distinct species having a basal relationship among remaining hadrosaurids.
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