1. The Cenozoic Era Geology 103

2. Following the Mesozoic extinctions, – marine invertebrates diversified giving rise to the present-day familiar marine fauna Overall, we can think of the Cenozoic Era – as a time during which Earth's flora and fauna became increasingly familiar Cenozoic rocks are more easily accessible – at or near the surface, so we know more about Earth and life history for this time than for any previous eras. Increasingly Familiar

3. Cenozoic rocks are especially widespread in western North America – although they are also found along the Gulf and Atlantic coasts As a result, we have a particularly good fossil record for many organisms – Several of national parks and monuments in the West feature displays of fossil mammals, including: Agate Fossil Beds National Monument in Nebraska, Badlands National Park in South Dakota, John Day Fossil Beds National Monument in Oregon Hagerman Fossil Beds National Monument in Idaho Good Fossil Records

4. Mammals evolved during the Late Triassic, – and some Mesozoic mammals retained characteristics of their ancestors, the cynodonts. By Cenozoic time, mammals had clearly differentiated from their ancestors. Evolution of Mammals

5. Angiosperms (flowering plants) continued to dominate land plant communities and now constitute more than 90% of all land plants Birds evolved during the Jurassic, perhaps earlier – the families now common appeared during the Paleogene and Neogene, reached their maximum diversity during the Pleistocene Epoch, and have declined slightly since then Other Biological Events

6. What periods are in the Cenozoic? The basic problem is that there aren’t many “big” mass extinctions in this era!

7. Zuni transgression ends; Tejas begins

8. Antarctica separates from Australia, heads to the South Pole (Eocene)

9. Eocene thermal maximum Around 55 my ago, temperatures worldwide increased to levels similar to the early Mesozoic Cause is uncertain, but may have involved increased atmospheric methane due to warming of ocean floor releasing methane from methane clathrates Caused many reptilian and mammalian orders to go extinct

10. Climate story of the Cenozoic is cooling

11. Grasses: a new type of photosynthesis C4 plants evolved in the Oligocene as a response to lowering CO 2 levels, drought conditions and other environmental stresses. Arose in many families of plants simultaneously; a good example of convergent evolution

12. Whales: another study of convergent evolution Eocene hippo-like terrestrial mammals to Oligocene marine mammals Evolution of whales stumped Darwin Molecular biology and discovery of transitional forms helped explain history

13. Cope’s rule Edwin Drinker Cope (1870) proposed this rule to describe the changes in size of organisms as they evolved As time progresses, organisms of the same clade increase in size Horses over the Cenozoic are a good example

14. Himalayan orogeny occurs in Pliocene and continues today India detaches from Gondwana and heads north Collides with Asia about 10 my at a (tectonically) rapid rate Raises Himalayas, Tibetan Plateau, Tien Shan Causes northern subtropical jet stream to split around the uplift, and repositions the high and low pressure areas over the Pacific

15. Cenozoic climate trend is drier 5.96 my – Strait of Gibraltar closes 5.96 – 5.33 my – Messinian salinity crisis 5.33 my – Zanclean flood event

16. Closing of Panama isthmus Subduction-related volcanism closes isthmus about 3 my Allowed ice sheets in Northern hemisphere to form More salty water in Atlantic Water sinks because it cools as it heads north Releases heat as it sinks, so polar oceans never get warmer water

17. Ice ages start up about 2 my ago Why then? Several factors need to be in place: polar continent, north/south-oriented oceans, split in the sub-tropical jet stream At that point, subtle factors can determine whether the glaciers build up or not

18. Milankovitch cycles Milutin Milankovitch (University of Belgrade, Serbia) proposes that “orbital parameters” that vary in a cyclic fashion over tens of thousands of years will determine that amount of solar insolation that reaches the Earth’s surface

19. Evidence of Pleistocene glaciations