After the dinosaurs died, sharks ruled the seas and jungles reached the poles
When an asteroid ended the age of dinosaurs 66 million years ago, it opened the Cenozoic, the era we still live in. Early on, the planet warmed until jungles spread to the poles and oversized birds dominated the food web. Mammals only later grew to enormous sizes.
The Cenozoic, meaning new life, covers the last 66 million years and follows the Mesozoic and Paleozoic. It began with the Cretaceous-Paleogene extinction, which most experts blame on the Chicxulub impactor. The British geologist John Phillips proposed the name in 1840, spelling it Kainozoic. With the non-avian dinosaurs gone, mammals and birds diversified rapidly, which is why the era is nicknamed the Age of Mammals: placentals dominated the north, marsupials the south. The continents also drifted into their present positions.
It is divided into the Paleogene, Neogene and Quaternary periods; the old Tertiary was formally replaced in 2004. During the Paleocene, from 66 to 56 million years ago, modern placental mammals appeared. The loss of big herbivores let dense but species-poor forests spread. India and every continent stood apart, a Tethys Sea divided Africa from Eurasia, and no land bridge yet joined the Americas. With large marine reptiles extinct, sharks dominated the oceans, while archaic predators called creodonts roamed on land.
The Eocene, from 56 to 33.9 million years ago, opened hot, with carbon dioxide around 1,400 parts per million and little difference in temperature between pole and equator. Early primates, whales and horses lived in the forests, and huge birds such as Paracrax sat at the top of food chains. Then, in the mid-Eocene, a current began circling Antarctica, disrupting ocean circulation and cooling the globe. Jungles shrank, seasons returned, grasses evolved, and mammals such as Andrewsarchus and nearly aquatic whales grew very large. An extinction closed the epoch, known in Europe as the Grande Coupure.
Grasslands spread in the Oligocene, from 33.9 to 23.03 million years ago, and the first elephants, cats and dogs appeared. The long trend was cooling and drying, capped by the Quaternary ice ages. Because its rocks are young and well preserved, the Cenozoic is known in more detail than any other era.
Source: Cenozoic
