TYRANNOSAURUS AND TRICERATOPS IN LOWER HELL CREEK BONE BED

Bone beds in the Hell Creek Formation (Maastrichian) of northeast Montana are rare. Rarer still are bone beds of mixed specimens. In 2006 we discovered a bone bed in lower Hell Creek Formation containing parts of Triceratops and T. rex lying together. The site is in the Snow Creek drainage northwest of Jordan, Montana. Recent erosion has exposed a continuous section of Bear Paw shale, Fox Hills sand and lower Hell Creek sands and clays. Lowest Hell Creek is a thick channel sand incised into Fox Hills beach sands. Resting on top of the channel sand is a sequence of alternating clay and sand units typical of the Hell Creek Formation.

The bone bed is in the middle of the first clay unit on top of the basal Hell Creek channel sand. The bones rest on a dark gray, tough clay containing abundant plant fragments. The bones are encased in a light gray clay containing carbonized roots in growth position and other plant remains. Quality of preservation in the bone bed ranges from excellent to some elements that appear to have been weathered or crushed prior to burial. The upper surface of some bones appear to have been burned prior to burial and a thin charcoal layer is present in the clay at the bone level.

Most of the fossils are from a sub-adult T .rex. However, two Triceratops brow horns and a right dentary were with the T. rex elements. Specimens include disarticulated skull bones, cervical ribs, dorsal ribs, ilia, ischia, a tibia, fibulae, femurs, one dorsal vertebra, one caudal vertebra and as yet unidentified fragments. At the same level and approximately 100 meters away was the overturned top of an adult Triceratops skull with both brow horns and attached parietal. All specimens are in preparation at the St. Louis Science Center.