Spring was in full swing along the Tanis River that day. It curved lazily through forest and wetland on its way to the Western Interior Seaway, a shallow sea several miles away that covered much of what is now North America’s Great Plains. Winter’s chill, when temperatures dipped to just above freezing, was a distant memory, but the full heat of summer had not yet arrived. Plants were budding or starting to bloom, and turtles rested along the river banks, taking what warmth they could from the sun. The river…
