Paleocene

The Paleocene IPA: /ˈpæli.əsiːn, -i.oʊ-, ˈpeɪli-/ PAL-ee-ə-seen, -⁠ee-oh-, PAY-lee-), or Palaeocene, is a geological epoch that lasted from about 66 to 56 million years ago. It is the first epoch of the Paleogene Period in the modern Cenozoic Era. The name comes from Ancient Greek words meaning "old" and "new", translating to "the old part of the Eocene".

This time period began after the K–Pg extinction event, when an asteroid hit Earth and caused many species to disappear, including the non-avian dinosaurs. The Paleocene was a time of recovery and change on Earth. The climate was warm, with no ice sheets at the poles, and forests grew even at high latitudes.

During the Paleocene, the continents were still moving. The Rocky Mountains were beginning to form, and the Indian Plate was moving toward Asia. In the oceans, life was also changing. Mammals began to diversify, and the first placental and marsupial mammals appeared. The end of the Paleocene was marked by a major climate event called the Paleocene–Eocene Thermal Maximum (PETM), which changed the Earth's climate.

Etymology

The word "Paleocene" was first used in 1874 by French scientist Wilhelm Philipp Schimper. It comes from Ancient Greek words meaning "old" and "new", specifically referring to "the old part of the Eocene". The Eocene epoch is when modern life began, and the Paleocene comes right before it.

Over time, scientists have agreed on how we divide Earth's history. In 1978, the Paleocene was officially named the first epoch of the Paleogene Period, along with the Eocene and Oligocene. Today, we use the spelling "Paleocene" in North America and mainland Europe, while "Palaeocene" is used in the UK.

Geology

The Paleocene Epoch was the time right after the K–Pg extinction event. This event ended the Cretaceous Period and the Mesozoic Era. The Paleocene lasted for about 10 million years, from 66 to 56 million years ago. It was the first part of the Cenozoic Era and the Paleogene Period. During this time, the Earth changed a lot. Important coal and natural gas formed.

Geologists split the Paleocene into three main ages: the Danian, Selandian, and Thanetian. These ages help scientists study the rocks and fossils from this time. The end of the Paleocene had a big warming event called the Paleocene–Eocene thermal maximum. This changed the oceans and affected many sea creatures.

Paleogeography

During the Paleocene, the continents kept moving toward where they are today. In the north, land bridges linked North America and Eurasia. These included Beringia between North America and East Asia, and paths through Greenland and Scandinavia.

The Rocky Mountains in North America were still growing because of earth movements. Volcanism in the North Atlantic made a big area of lava, which may have helped create the North Atlantic Ocean and changed the climate. In the south, the continents of Gondwanaland kept splitting apart, with Antarctica still linked to South America and Australia. Africa moved closer to Europe, and the Indian subcontinent was heading toward Asia.

Climate

The Paleocene climate was warm and tropical. The poles were temperate, and there were no ice caps. The average global temperature was around 24–25 °C (75–77 °F), much warmer than today’s average.

Different parts of the world had varied climates. Some areas were tropical, others arid, and some had humid weather. The oceans were warm, too. There were changes in climate during this time, influenced by things like volcanic activity.

Flora

The warm, wet climate of the Paleocene helped tropical and subtropical forests grow. These forests had conifers and broad-leafed trees. In places like Patagonia, there were tropical rainforests, cloud rainforests, mangrove forests, swamp forests, savannas, and sclerophyllous forests. Fossils from Colombia and North Dakota show that many modern plant families, like palm trees, legumes, and aroids, existed then, just as they do today.

With large herbivorous dinosaurs gone, forests grew thicker. Plants found new ways to survive, such as growing taller to reach sunlight or making larger seeds to help seedlings. Wildfires happened less because there was less oxygen in the air. After the mass extinction event that ended the age of dinosaurs, many plant species died out, but ferns were often the first to grow back, helping to restore the forests. Over time, flowering plants became more common, evolving with the insects that pollinated them and the animals that ate their fruits.

Fauna

In the K–Pg extinction event, all land animals larger than 25 kg were lost. This opened up space for new animals to live.

Mammals

Mammals first appeared in the Late Triassic. They stayed small and active at night during the time of dinosaurs, to avoid being eaten. By the Middle Jurassic, they lived in many different places. In general, Paleocene mammals stayed small until the end of the time period. After the K–Pg extinction event, mammals changed quickly and filled the empty places. Modern mammals are split into three groups: placentals, marsupials, and monotremes. All three groups began in the Cretaceous. Paleocene marsupials include Peradectes, and monotremes Monotrematum. This time saw the start of many groups such as the earliest afrotherian Ocepeia, xenarthran Utaetus, rodent Tribosphenomys and Paramys, early primates the Plesiadapiformes, the first carnivorans Ravenictis and Pristinictis, and possible early pangolins Palaeanodonta. After the K–Pg extinction event, mammals grew larger and started to eat fruit and other foods.

Birds

According to DNA studies, modern birds changed quickly after the other dinosaurs went extinct in the Paleocene. Almost all modern birds began in this time, except for fowl and palaeognaths. This was one of the fastest changes for any group, likely because of new fruit trees and insects. The fossil record for birds in the Paleocene is not very strong, with most being waterbirds like the early penguin Waimanu. The earliest arboreal bird known is Tsidiiyazhi, a mousebird from about 62 million years ago. The fossil record also includes early owls such as Berruornis from France, and Ogygoptynx from the United States.

Reptiles

It is believed all non-avian dinosaurs went extinct at the K–Pg extinction event 66 million years ago. After this event, many lizards and snakes went extinct, but most groups had already existed by the Cretaceous. Only small squamates are known from the early Paleocene—the largest snake Helagras was 95 cm long—but the late Paleocene snake Titanoboa grew to over 13 m long, the longest snake ever known. Kawasphenodon peligrensis from South America is the youngest record of Rhynchocephalia outside of New Zealand.

Freshwater crocodilians survived the K–Pg extinction event, likely because freshwater areas were not as affected as ocean areas. One example is Borealosuchus, which averaged 3.7 m in length. Turtles were not greatly affected by the K–Pg extinction event, and many species survived.

Amphibians

There is little evidence that amphibians were greatly affected by the K–Pg extinction event, likely because the freshwater areas they lived in were not as impacted as ocean environments. The true toads evolved during the Paleocene.

Fish

The small pelagic fish population recovered quickly, and few sharks and rays went extinct. Overall, only 12% of fish species were lost. After the K–Pg extinction event, ray-finned fish became more common and larger, and rose to dominate the open oceans. Acanthomorphs—a group of ray-finned fish—changed quickly and became a large part of marine life by the end of the Paleocene.

Insects and arachnids

Insect recovery changed depending on the place. The middle-to-late Paleocene French Menat Formation had many beetles—such as weevils, jewel beetles, leaf beetles, and reticulated beetles—as well as other insects like pond skaters, cockroaches, orthopterans, hymenopterans, butterflies, and flies.

Marine invertebrates

Among marine invertebrates, plankton and those with a planktonic stage were most affected by the K–Pg extinction event. However, the quick change in large fish species shows that plankton populations were healthy through the Paleocene. Marine invertebrate diversity may have taken about 7 million years to recover. Sand dollars first evolved in the late Paleocene.