Paleoecology
Edmontosaurus was a wide-ranging genus in both time and space. The rock units from which it is known can be divided into two groups by age: the older Horseshoe Canyon and St. Mary River formations, and the younger Frenchman, Hell Creek, and Lance formations. The time span covered by the Horseshoe Canyon Formation and equivalents is also known as Edmontonian, and the time span covered by the younger units is also known as Lancian. The Edmontonian and Lancian time intervals had distinct dinosaur faunas.
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