Cenozoic

Mammals are the dominant terrestrial vertebrates of the Cenozoic.

The Cenozoic (also Caenozoic or Cainozoic) Era (pronounced /ˌsiːnəˈzoʊɪk/, /ˌsɛn-/) (meaning "new life" (Greek καινός (kainos), "new", and ζωή (zoe), "life"), is the most recent of the three classic geological eras and covers the period from 65.5 million years ago to the present. It is marked by the Cretaceous–Tertiary extinction event at the end of the Cretaceous that saw the demise of the last non-avian dinosaurs and the end of the Mesozoic Era. The Cenozoic era is ongoing.

Subdivision

The Cenozoic Era is divided into two periods, the Paleogene and Neogene, and they are in turn divided into epochs. The Paleogene consists of the Paleocene, Eocene, and Oligocene epochs, and the Neogene consists of the Miocene, Pliocene, Pleistocene, and Holocene epochs, the last of which is ongoing. Historically, the Cenozoic has been divided into periods (or sub-eras) named the Tertiary (Paleocene through Pliocene) and Quaternary (Pleistocene and Holocene).

Tectonics

Geologically, the Cenozoic is the era when the continents moved into their current positions. Australia-New Guinea split from Gondwana and drifted north and, eventually, adjacent to South-east Asia; Antarctica moved into its current position over the South Pole; the Atlantic Ocean widened and, later in the era, South America became attached to North America.

India collided with Asia between 55 and 45 million years ago; Arabia collided with Eurasia, closing the Tethys ocean, around 35 million years ago.^[4]

Climate

The Cenozoic Era has been a period of long-term cooling. In the early Cenozoic, particulate ejecta from the K-T boundary impact blocked incoming solar radiation . After the tectonic creation of Drake Passage, when Australia fully detached from Antarctica during the Oligocene, the climate cooled significantly due to the advent of the Antarctic Circumpolar Current which brought cool deep Antarctic water to the surface. Warm conditions returned in the Miocene due to uncovered gas hydrates releasing carbon dioxide. When South America became attached to North America creating the Isthmus of Panama, the Arctic region cooled due to the strengthening of the Humboldt and Gulf Stream currents, eventually leading to the Last Glacial Maximum or the last ice age.

Life

The Cenozoic Era is the age of new life. During the Cenozoic, mammals diverged from a few small, simple, generalized forms into a diverse collection of terrestrial, marine, and flying animals, giving this period its other name, the Age of Mammals. The Cenozoic is just as much the age of savannas, or the age of co-dependent flowering plants and insects. Grass also played a very important role in this epoch, shaping the evolution of the birds and mammals that fed on it. One group that diversified significantly in the Cenozoic as well were the snakes. Evolving in the Cenozic, the snakes evolved into a huge amount of forms, especially colubrids, following the evolution of their current prey source, the rodents.

In the earlier part of the Cenozoic, the world was dominated by the gastornid birds, terrestrial crocodiles like Pristichampsus, and a handful of primitive large mammal groups like uintatheres, mesonychids, and pantodonts. But as the forests began to receed and the climate began to cool, other mammals took over. The cenozoic is full of mammals both strange and familiar, including chalicotheres, oreodonts, whales, primates, entelodonts, saber-toothed cats, mastodons and mammoths, three-toed horses, giant rhinos like Indricotherium, and brontotheres, just to name a few.

See also

• Geologic Time Scale
• K-T Boundary

References

Bibliography

• British Caenozoic Fossils, 1975, The Natural History Museum, London.
• Geologic Time, by Henry Roberts.