Reworking of Cretaceous dinosaurs into Paleocene channel, deposits, upper Hell Creek Formation, Montana
Dinosaur teeth from Paleocene channel fills have been interpreted as indicating dinosaur survival into the Paleocene. However, enormous potential for reworking exists because these records are restricted to large channel fills that are deeply incised into Cretaceous strata. Identification of reworked fossils is usually equivocal. This problem is illustrated by the Black Spring Coulee channel fill, a dinosaur-bearing Paleocene deposit in the upper Hell Creek Formation of eastern Montana. In this example, the reworked nature of well-preserved dinosaur bones is apparent only after detailed sedimentological and palynological analysis. Because of the potential for reworking, dinosaur remains derived from Paleocene fluvial deposits should not be assigned a Paleocene age unless they (1) are found in floodplain deposits, (2) are articulated, (3) are in channels that do not incise Cretaceous strata, or (4) are demonstrably reworked from Paleocene deposits. To date, reports of "Paleocene" dinosaurs do not fulfill any of these criteria. Thus, the proposal that dinosaurs persisted into the Paleocene remains unsubstantiated.