Rounded and polished igneous or metamorphic pebbles that occur in sedimentary deposits generally are considered to be true gastroliths only when associated with the remains of vertebrate animals. In the Kansas Cretaceous, with the exception of two unusual specimens, a shark and a mosasaur, gastroliths are known to be associated only with the remains of extinct marine reptiles called plesiosaurs (Sauropterygia; Plesiosauroidea). Examples of non-associated, gastrolith-like stones are rare in the fossil record of Kansas. The recent discovery of rounded and polished stones from two localities in the basal Kiowa Shale (Albian, Early Cretaceous) coincides with the documented presence of plesiosaur remains in that formation, including one specimen associated with over 200 gastroliths. Similar sized stones collected from the underlying Cheyenne Sandstone were composed predominately of quartz and are lithologically distinct from the probable gastroliths. The rounded, polished appearance of these stones, including chert pebbles with distinctive conchoidal fractures, strongly suggests that the stones from the basal Kiowa Shale are gastroliths.
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Vol. 108 • No. 3