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Deformed teeth are found as rare components of the dentitions of both modern and fossil chondrichthians. Tooth deformities occur as bent or twisted tooth crowns, missing or misshaped cusps, atypical protuberances, perforations, and abnormal root structures. Deformed tooth files consisting of unusually overlapped or small teeth, or teeth misaligned in the jaw also occur in modern forms, but deformed tooth files generally are not recognizable in fossils due to post‐mortem dissociation of teeth and jaws. A survey of 200 modern lamniform and carcharhiniform sharks as well as literature sources indicate that such deformities are produced by feeding‐related injury to the tooth‐forming tissue of the jaws, particularly by impaction of chondrichthian and teleost fin and tail spines. Tooth counts for several late Cretaceous genera, based on material recovered from coastal plain sites from New Jersey to Alabama, suggest that the frequency of occurrence of deformed teeth in a species varies from about 0.015% in Squalicorax kaupi to about 0.36% in Paranomotodon sp. Tooth counts for modern lamniform and carcharhiniform sharks yield a comparable range in frequency of tooth deformities. Variation in frequency of tooth deformity may reflect interspecific differences in feeding behavior and dietary preferences. There is no suggestion in our data of any strong patterns of temporal variation in tooth deformity frequency, or of patterns ­reflecting chondrichthian phylogenetic history and evolution. Skeletal components of the probable prey of the Cretaceous species are preserved in the same horizons as the deformed teeth, and also are found within co‐occurring chondrichthian coprolites.

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DeGrey facies…………………………………………………………. 15 Verendrye facies………………………………………………………. The Campanian-Maestrichtian boundary unconformity………….. Virgin Creek facies…………………………………………………… Mobridge facies………………………………………………………. Elk Butte facies ………………………………………………………. Fox Hills Formation……………………………………………………………. The Cretaceous-Tertiary boundary in Badlands National Park………………………………. A historical perspective on the Interior Zone ………………………………….. The Disturbed Zone……………………………………………………………………… Conata Creek locality…………………………………………………………. Grassy Tables Overlook locality………………………………………………. Wilderness Access Trailhead locality………………………………………. Buffalo Gap National Grasslands locality…………………………………… Dry Creek locality………………………………………………………………. Unnamed marine facies (upper Fox Hills Formation)………………………………. Tertiary Geology of Badlands National Park…………………………………………………… Historical overview of the White River Group………………………………………… The Yellow Mounds and Interior paleosols……………………………………………. Chamberlain Pass Formation……………………………………………………………49 Chadron Formation………………………………………………………………………. Brule Formation……………………………………………………………………………51 The Pig Dig site………………………………………………………………… Sharps Formation………………………………………………………………………… The Quaternary Landscape………………………………………………………………………. Three rivers over time…………………………………………………………………….54 Stream terraces: can they tell us about past climatic conditions?………………….. Quaternary and late Tertiary time scale (stages and stades)………………………..55 Weathering, mass wasting, and erosion………………………………………………. Castles, monuments, sod tables, and hoodoos………………………………………. Acknowledgments…………………………………………………………………………………. Selected Internet links…………………………………………………………………………….. Selected references………………………………………………………………………………..