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Evidence of Reworked Cretaceous Fossils and Their Bearing on the Existence of Tertiary Dinosaurs

Jeffrey G. Eaton, James I. Kirkland and Kentaro Doi
PALAIOS
Vol. 4, No. 3 (Jun., 1989), pp. 281-286
DOI: 10.2307/3514776
Stable URL: http://www.jstor.org/stable/3514776
Page Count: 6
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Evidence of Reworked Cretaceous Fossils and Their Bearing on the Existence of Tertiary Dinosaurs
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Abstract

The Paleocene Shotgun fauna of Wyoming includes marine sharks as well as mammals. It has been suggested that the sharks were introduced from the Cannonball Sea. It is more likely that these sharks were reworked from a Cretaceous rock sequence that included both marine and terrestrial deposits as there is a mixture of marine and freshwater taxa. These taxa have not been recorded elsewhere after the Cretaceous and are not known from the Cannonball Formation. Early Eocene localities at Raven Ridge, Utah, similarly contain teeth of Cretaceous marine and freshwater fish, dinosaurs, and Eocene mammals. The Cretaceous teeth are well preserved, variably abraded, and serve to cast doubts on criteria recently used to claim that dinosaur teeth recovered from the Paleocene of Montana are not reworked. Another Eocene locality in the San Juan Basin has produced an Eocene mammalian fauna with diverse Cretaceous marine sharks. Neither the nature of preservation nor the degree of abrasion could be used to distinguish reworked from contemporaneous material. The mixed environments represented by the fish taxa and recognition of the extensive pre-Tertiary extinction of both marine and freshwater fish were employed to recognize reworked specimens.

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