Section 7: Cenozoic Era
The Cenozoic Era, the most recent era, began about 65 million years ago. This era is divided into two periods, the Tertiary (ter-she-air-ee) and Quaternary (kwat‑er-nair-ee).
Today, geologists have divided the Tertiary Period into two new periods—the Paleogene and Neogene. The Tertiary Period lasted about 65 million years ago to about 1.8 million years ago, a time-span of about 64 million years.
The Cenozoic Era is sometimes called the “Age of Mammals” because after the dinosaurs became extinct, warm‑blooded mammals took over. For the first several million years of the Tertiary Period, the weather was quite warm with sea water continuing to advance and recede every few million years. Sharks and stingrays lived in North Dakota seas at that time.