1. www.geo.ucalgary.ca/~macrae/timescale/time_scale.gif Cenozoic Life

2. The Cenozoic was the time during which –Earth’s present-day fauna and flora evolved –trends established millions of years earlier continued Fewer skull and jaw bones during the transition –from fish to amphibians –and then to reptiles –and finally to mammals Cenozoic Life History

3. Cenozoic rocks are especially common –in western North America –also found along the Gulf and Atlantic coasts –horses, rhinoceroses, rodents, rabbits, and camels have very good fossil records Good Fossil Records

4. Changing climatic patterns –accompanied by shifting plant distributions characterize the Tertiary During the Paleocene and Eocene –mean annual temperatures were high –abundant precipitation fell –tropical to semitropical forests covered much of North America Changing Climatic Patterns

5. Leaf structure can give information about: –Paleoprecipitation –Paleotemperature Precipitation: drip tips –Reduces fungal infections –Reduces parasitic plant infections Temperature: degree of leaf serration –Correlation between big smooth leaves (entire margin) and warm climates Not clear why Leaf Structure

6. Climatic trends for four areas in North America Plant leaves as Climatic Indicators –based on the percentages of plant species with entire margin leaves

7. A major climatic change took place at the end of the Eocene Major Climatic Change –when mean annual temperatures dropped 7 degrees C in 3 million years

8. Since the Oligocene –mean annual temperatures have varied somewhat worldwide –overall have not changed much in the middle latitudes except during the Pleistocene Climatic Change

9. A general decrease in precipitation –over the last 25 million years –in the midcontinent region of North America As the climate became drier vast forests of the Oligocene –gave way first to savanna conditions grasslands with scattered trees –and finally to steppe environments short-grass prairie of the desert margin Decrease in Precipitation

10. With the demise of dinosaurs and their relatives –mammals adaptively radiated –remarkable diversification continued throughout the Cenozoic Era The Age of Mammals had begun Mammal Diversification

11. Marsupial mammals give birth to live young –born in a very immature, almost embryonic condition –undergo further development in the mother's pouch Marsupials probably migrated to Australia, –the only area in which they are common today, –via Antarctica before Pangaea fragmented completely Marsupial Mammals

12. Quite widespread in South America until a few millions of years ago Most South American marsupials died out –when a land connection was established between the Americas –and placental mammals migrated south Now the only marsupials –outside Australia and some nearby islands are species of opossums South American Marsupials

13. Like marsupials, placental mammals give birth to live young, –but their reproductive method –differs in important details In placentals, the amnion of the amniote Placenta –has fused with the walls of the uterus –forming a placenta

14. Nutrients and oxygen flow –from mother to embryo through the placenta –permitting the young to develop much more fully before birth marsupials also have a placenta –but it is less efficient –explaining why their newborn are not as fully developed Marsupial Placenta Less Efficient

15. A measure of the success of placental mammals –is partially related to their method of reproduction More than 90% of all mammals –fossil and extinct, are placentals Success of Placental Mammals

16. With the possible exception of camels, –no group of mammals has a better fossil record horse fossils are so common, –especially in North America –where most of their evolution took place –that their overall history and evolutionary trends are quite well known Fossil Record of Horses

17. Some evolutionary trends in horses –an increase in size –lengthening of the limbs –reduction in the number of toes –development of high- crowned teeth with complex chewing surfaces Horse Evolution

18. Size increase Legs and feet become longer: for running Lateral toes reduced to vestiges Straightening and stiffening of the back Adaptations for grinding abrasive grasses Larger, more complex brain Trends in Horses

19. Horse evolution proceeded along two distinct branches One led to three-toed browsing horses –all now extinct The other led to three-toed grazing horses –and finally to one-toed grazers The appearance of grazing horses –with high-crowned chewing teeth –coincided with the evolution and spread of grasses during the Miocene Horse Evolution Branched

20. Once grasses had evolved –many hoofed mammals became grazers –developed high-crowned, abrasion-resistant teeth Low- and High-Crowned Teeth Low-crowned teeth –typical of many mammals with varied diets High-crowned, cement-covered chewing teeth –are adapted for grazing

21. The most remarkable aspect –of the Pleistocene mammalian fauna –is that so many very large species existed Mastodons, mammoths, giant bison, –huge ground sloths, immense camels, beavers 2 m tall –present in North America Mammals of the Ice Age

22. Many smaller mammal species also existed –but obvious trend among Pleistocene mammals was large body size Perhaps this was an adaptation –to the cooler conditions Large animals have less surface area –compared to their volume –thus retain heat more effectively than do smaller animals –(but what about big dinosaurs?) Cooler Conditions—Larger Sizes

23. Some of the world's best-known fossils –come from Pleistocene deposits –frozen mammals found in Siberia and Alaska, –such as mammoths, bison, and a few others These extraordinary fossils, –although very rare, –provide much more information than most fossils do Frozen Mammals

24. Frozen baby mammoth found –in Siberia in 1971 Frozen Baby Mammoth –1.15 m long and 1.0 m tall –had a hairy coat Recovered from permafrost

25. Extinctions have occurred continually –at times of mass extinctions, Earth's biotic diversity sharply declined –as at the ends of the Paleozoic and Mesozoic eras In marked contrast, –the Pleistocene extinctions were rather modest –did have a profound effect on genera of large terrestrial mammals Pleistocene Extinctions

26. (1) What caused these extinctions? (2) Why did these extinctions eliminate mostly large mammals? (3) Why were extinctions more severe in Australia and the Americas? No completely satisfactory explanation exists –but two competing hypotheses are currently being debated Extinctions

27. Rapid climatic changes at the end of the Pleistocene Prehistoric overkill –holds that human hunters were responsible Extinction Hypotheses

28. Rapid changes in climate and vegetation –occurred over much of Earth's surface during the Late Pleistocene –as glaciers began retreating In North America and northern Eurasia –conifer and broadleaf forests replaced open- steppe tundras –warmer and wetter conditions prevailed Climate and Vegetation Changes

29. The southwestern U.S. region changed –from a moist area with numerous lakes where saber-toothed cats, giant ground sloths, and mammoths roamed –to a semiarid environment unable to support a diverse large mammalian fauna Climate and Vegetation Changes

30. Rapid changes in climate and vegetation –can certainly affect animal populations –but the climate hypothesis presents several problems First, why didn't the large mammals migrate to more suitable habitats as the climate and vegetation changed? –many other animal species did Why Didn't Large Mammals Migrate?

31. For example, reindeer and the Arctic fox –lived in southern France during the last glaciation –migrated to the Arctic when the climate became warmer Mammal Migration in Europe

32. The second argument against the climatic hypothesis –is the lack of correlation between extinctions and the earlier glacial advances and retreats throughout the Pleistocene Epoch Previous changes in climate –were not marked by episodes of mass extinctions Argument Against the Climatic Hypothesis

33. Proponents of the prehistoric overkill hypothesis –argue that the mass extinctions in North and South America and Australia coincided closely with the arrival of humans Perhaps hunters had a tremendous impact –on the faunas of North and South America –about 11,000 years ago because the animals had no previous experience with humans Arrival of Humans

34. The same thing happened much earlier in Australia soon after people arrived about 40,000 years ago No large-scale extinctions in Africa and most of Europe –because animals in those regions had long been familiar with humans Arrival of Humans

35. How could a few hunters decimate so many species of large mammals? Humans have caused major extinctions on oceanic islands –in a period of about 600 years after arriving in New Zealand, humans exterminated several species of the large, flightless birds called moas Extinctions on Oceanic Islands

36. A problem is that present-day hunters concentrate on smaller, abundant, and less dangerous animals –remains of horses, reindeer, and other small animals are found in many prehistoric sites in Europe –whereas mammoth and woolly rhinoceros remains are scarce Hunters Concentrate on Small Animals

37. Few human artifacts are found among the remains of extinct animals in North and South America –and there is usually little evidence that the animals were hunted Countering this argument –is the assertion that the impact on the previously unhunted fauna –was so swift as to leave little evidence Other Arguments

38. The reason for the extinctions –of large Pleistocene mammals is still unresolved It may turn out that the extinctions –resulted from a combination of different circumstances Populations that were already under stress from climatic changes –were perhaps more vulnerable to hunting –especially if smaller females and young animals were the preferred targets Multiple Reasons

39. How do we know we had ice ages? Geologic evidence: –Moraines –Poorly sorted sediments –Scratched rocks

40. Most important glacial deposits –chaotic mixtures of poorly sorted sediment deposited directly by glacial ice –An end moraine is deposited –when a glacier’s terminus remains stationary for some time Moraines Mt. Cook, 1999

41. If the glacier’s terminus –should recede and then stabilize once again –another end moraine forms –known as a recessional moraine Recessional Moraine

42. Features seen in areas once covered by glaciers glacial polish –the sheen striations –scratches? Glacial Features Devil’s Postpile National Monument, California

43. Glaciers typically deposit poorly sorted nonstratified sediment Glacial Sediment

44. How do we know how cold it got? Isotopes of oxygen! Oxygen: –All isotopes have 8 protons –Most common isotope has 8 neutrons –Extremely rare: 9 neutrons –Rare but detectable: 10 neutrons –(why are 10 and 8 more common than 9?)

45. Oxygen Isotope Ratio http://www.ngdc. noaa.gov/paleo/ ctl/about.html 18 O 16 O

46. Oxygen Isotope Ratio http://www.ngdc. noaa.gov/paleo/ ctl/about.html 18 O 16 O

47. Oxygen Isotope Ratio http://www.ngdc. noaa.gov/paleo/ ctl/about.html 18 O 16 O

48. QUATERNARY 60 Ma Today ~2 Ma - Northern Hemisphere 10,000 CENOZOIC ERA ~45 Ma - East Antarctic ~30 Ma - West Antarctic Cenozoic Glaciations Onset of the Ice Age

49. Why the Icehouse? Long-term climate drivers: –Plate tectonics Opening/closing of seaways –Ocean currents are our heat and AC Uplift and erosion of mountains –Weathering reduces atmospheric CO2 –Life: catastrophic evolution of new capabilities –O2 –Astronomical drivers Other bodies (moon, sun) pull on the Earth, changing its distance to the sun

50. Milutin Milankovic