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Gradual Dinosaur Extinction and Simultaneous Ungulate Radiation in the Hell Creek Formation
Robert E. Sloan, J. Keith Rigby, Leigh M. Van Valen and Diane Gabriel
New Series, Vol. 232, No. 4750 (May 2, 1986), pp. 629-633
Published by: American Association for the Advancement of Science
Stable URL: http://www.jstor.org/stable/1696921
Page Count: 5
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Dinosaur extinction in Montana, Alberta, and Wyoming was a gradual process that began 7 million years before the end of the Cretaceous and accelerated rapidly in the final 0.3 million years of the Cretaceous, during the interval of apparent competition from rapidly evolving immigrating ungulates. This interval involves rapid reduction in both diversity and population density of dinosaurs. The last dinosaurs known are from a channel that contains teeth of Mantuan mammals, seven species of dinosaurs, and Paleocene pollen. The top of this channel is 1.3 meters above the likely position of the iridium anomaly, the Cretaceous/Tertiary boundary.
Science © 1986 American Association for the Advancement of Science