Paleocene

American  

[pey-lee-uh-seen, pal-ee-] / ˈpeɪ li əˌsin, ˈpæl i- /

adjective

1. noting or pertaining to an epoch of the Tertiary Period, from 65 to 55 million years ago, and characterized by a proliferation of mammals.

---

noun

1. the Paleocene Epoch or Series.

Paleocene Scientific  

/ pā′lē-ə-sēn′ /

1. The earliest epoch of the Tertiary Period, from about 65 to 58 million years ago. During this time, the Rocky Mountains formed and sea levels dropped, exposing dry land in North America, Australia, and Africa. Many new types of small mammals evolved and filled the niches left empty after the extinctions that ended the Cretaceous Period. Soft-bodied squid replaced the ammonites as the dominant form of mollusk.

2. See Chart at geologic time

---

Etymology

Origin of Paleocene

First recorded in 1875–80; paleo- + -cene

Example Sentences

The same temperature-related patterns that once defined dinosaur ecosystems continued into the Paleocene epoch, guiding how life recovered after the disaster.

From Science Daily • Oct. 26, 2025

The majority of known Podonominae fossils originate from the Northern Hemisphere, with only two prior exceptions documented from the Southern Hemisphere: an Eocene specimen from Australia and a Paleocene record from India.

From Science Daily • Oct. 15, 2025

These tracks might have been made by a creodont, a predatory mammal about the size of a house cat, which flourished in the Paleocene and Eocene in Europe, Africa and North America.

From Seattle Times • Sep. 15, 2023

Scientists have debated these questions since the 1870s, when the first fossils of Paleocene placental mammals emerged in New Mexico.

From Scientific American • May 17, 2022

“An act? No. If anybody is acting, it’s us. She’s as real as”—he looked around; he picked up the tiny, wedgelike skull of Barney, a 60-million-year-old Paleocene rodent, and held it up—“as real as Barney.”

From "Stargirl" by Jerry Spinelli