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REPTILES OF THE TIMBER LAKE MEMBER (CRETACEOUS: MAASTRICHTIAN), FOX HILLS FORMATION, NORTH DAKOTA

HOGANSON, John W., North Dakota Geological Survey, 600 East Blvd., Bismarck, ND 58505
ERICKSON, J. Mark, and GETMAM, Myron R. C., Geology Dept., St. Lawrence University, Canton, NY 13617
   

Compared with invertebrates, vertebrate fossils are sparse in the Fox Hills Formation of North Dakota. The vertebrate fauna of this marine and lagoonal formation is therefore poorly known. Vertebrate fossils occur only as isolated skeletal elements in assemblages dominated by teeth from marine fishes. Reptile fossils are occasionally found associated with the fish.

In North Dakota, exposures of the Cretaceous (Maastrichtian) Fox Hills Formation occur in both the south-central and southwestern portions of the state. Reptile remains have been recovered from the marine near-shore sandstones and siltstones of the Timber Lake Member of the Fox Hills Formation from both areas at five localities (Emmons, Burleigh and Bowman counties). The reptilian fauna consists of a mix of marine and terrestrial taxa and includes teeth of the mosasaurs Mosasaurus dekayi, and Plioplatecarpus sp., two indeterminate mosasaur vertebrae, a row of ornately sculptured tubercles of the trionychoid turtle Basilemys sp., teeth of the crocodylian Leidyosuchus? sp., and a tooth of an indeterminate tyrannosaurid. Three additional specimens, perhaps representing a marine turtle, are as yet undetermined. None of these reptiles have been previously reported from the Fox Hills Formation of North Dakota. A Basilemys sp. has been reported from the formation in South Dakota, and A. G. Leonard reported a mosasaur tooth, presumed to be from the Fox Hills Formation, in the USGS Bismarck Folio of 1912. That specimen has not been found.

M. dekayi, Basilemys sp., Leidyosuchus? sp. and the tyrannosaurid tooth occur in the Jeletzkytes nebrascensis Western Interior ammonite Zone. This places them within the Globotruncana gansseri foraminiferal Zone of the Atlantic and Gulf Coasts and suggests they are of early Late Maastrichtian age.

   
 
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Updated: 08.11.06