Terry Schaeffer
Kirk R. Johnson
Douglas J. Nichols
John P. Hunter
Dean Pearson
2002
<p><span>Field surveys of the Upper Cretaceous </span>Hell<span> </span>Creek<span> </span>Formation<span> </span>in<span> </span>southwestern<span> </span>North<span> </span>Dakota<span> since 1986 have produced a total of 10124 specimens from 42 </span>vertebrate<span> microsites and an additional 41 dinosaur skulls or partial skeletons or skulls from separate sites representing 61 taxa of vertebrates dominated by fish, dinosaurs, turtles, and crocodilians. Common elements of this diverse fauna occur to within 2.37 m of the Cretaceous-Tertiary (K-T) boundary. The stratigraphically highest fossil </span>in<span> the study is a partial ceratopsian skeleton 1.77 m below the K-T boundary </span>in<span> the basal Fort Union </span>Formation<span>. All dinosaurs that occur at more than two sites also occur at the highest level that yielded more than 500 specimens (8.40 m below the K-T boundary). The fine-grained uppermost 2 m of the </span>Hell<span> </span>Creek<span> is nearly devoid of all fossils, including taxa known to occur </span>in<span> the overlying </span>formation<span>. The absence of channel deposits </span>in<span> this part of the </span>formation<span> may be the reason for the absence of fossil localities. The presence of marine-tolerant taxa suggests that the study area may have been adjacent to a previously unidentified seaway of latest Cretaceous age. Rarefaction analysis indicates no evidence for a decline </span>in<span> </span>vertebrate<span> diversity through the </span>formation<span> or dinosaurian diversity </span>in<span> the 3 m below the K-T boundary. Our results are not compatible with gradual </span>vertebrate<span> extinction at the end of the Cretaceous.</span></p>
application/pdf
10.1130/0-8137-2361-2.145
en
Geological Society of America
Vertebrate biostratigraphy of the Hell Creek Formation in southwestern North Dakota and northwestern South Dakota
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