Life of the Cenozoic Era

1. Chapter 18 Life of the Cenozoic Era

2. This mural from the Smithsonian Institution depicts what life was like at Agate Beds National Monument, Nebraska, during the Miocene Epoch

3. Cenozoic Biota • Recall that when Earth formed • it was hot, barren, and waterless, • the atmosphere was noxious, • it was bombarded by meteorites and comets • and no organisms existed • During the Precambrian, and Paleozoic and Mesozoic eras, • Earth and its organisms • took on their • present-day appearance

4. Geologically Short • Even though the Cenozoic • constitutes only 1.4% of all geologic time, • this comparatively brief episode • of only 66 million years of Earth and life history • was certainly long enough for considerable change to take place • Earth’s biota continues to change, • although most of the changes are minor • from our perspective, • but nevertheless important

5. Evolution of Mammals • Mammals evolved during the Late Triassic, • so they were contemporaries with dinosaurs • Some of the earliest mammals • differed little from their ancestors, • the cynodonts • but as they evolved they became increasingly familiar • During the Cenozoic, • they diversified into numerous types • that adapted to nearly all terrestrial habitats • as well as aquatic environments, • and one group, the bats, became fliers

6. Other Biological Events • Other equally important biological events • were taking place • Angiosperms, or flowering plants, • evolved during the Cretaceous • and soon became the dominant land plants, • and now constitute more than 90% of all land plant species • Their geographic distribution varied during the Cenozoic, • depending on changing climates • The first birds evolved during the Jurassic, • but the families now common • appeared during the Paleogene and Neogene, • reached their maximum diversity during the Pleistocene Epoch, • and have declined slightly since then

7. Increasingly Familiar • 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 more and more like what it is today • 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

8. Good Fossil Records • 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 our national parks and monuments in the west • feature displays of fossil mammals, • including Agate Fossil Beds National Monument, Nebraska, • Badlands National Park in South Dakota, • and John Day Fossil Beds National Monument in Oregon

9. early rhinoceroses tapirs Titanotheres standing 2.5m high at the shoulder ancient horses carnivores John Day Fossil Restoration • Restoration of Clarno Formation fossils • from Eocene age rocks in John Day Fossil Beds National Monument Oregon • The climate at this time was subtropical • and the lush forests of the region were occupied by

10. Eastern Mammal Fossils • Terrestrial deposits with land-dwelling fossil mammals • are not nearly as common in the east, • but Florida is a notable exception • Nevertheless, some eastern and southern states • such as Maryland, South Carolina, and Alabama • have deposits with the fossils • of Cenozoic marine mammals • as well as fossil invertebrates and sharks • The Alabama state fossil is Basilosaurus cetoides, • a fossil whale that lived during the Eocene

11. Messel Fossil Beds • Mammal fossils are found on other continents, too, • but certainly one of the most remarkable fossil sites • anywhere in the world • is the Messel fossil beds in Germany

12. Marine Invertebrates and Phytoplankton • The Cenozoic marine ecosystem • was populated mostly • by those plants, animals, • and single-cell organisms • that survived the terminal Mesozoic extinction • Gone were the ammonites, rudists, • and most of the planktonic foraminifera • Especially prolific Cenozoic invertebrate groups • were the foraminifera, radiolarians, corals, • bryozoans, mollusks, and echinoids

13. More Provincial • The marine invertebrate community • in general became more provincial • during the Cenozoic • because of changing ocean currents • and latitudinal temperature gradients • In addition, the Cenozoic marine invertebrate faunas • became more familiar in appearance

14. Species Diversified • Entire families of phytoplankton • became extinct at the end of the Cretaceous • with only a few species in each major group • surviving into the Paleogene • These species diversified and expanded • during the Cenozoic, • perhaps because • of decreased competitive pressures • Coccolithophores, diatoms, and dinoflagellates • all recovered from • their Late Cretaceous reduction in numbers • to flourish during the Cenozoic

15. Diatoms • Diatoms were particularly abundant • during the Miocene, probably • because of increased volcanism during this time • Volcanic ash provided • increased dissolved silica in seawater • which diatoms used to construct their skeletons • Massive Miocene diatomite rocks • are present in several western States

16. Diatomite • Outcrop of diatomite from the Miocene • Monterey Formation, Newport Lagoon, California

17. Diatoms • A pinnate diatom • and a centric diatom • from the Monterrey Formation, California

18. Foraminifera • The foraminifera were a major component • of the Cenozoic marine invertebrate community • Although dominated by relatively small forms, • it included some exceptionally large forms • that lived in the warm waters • of the Cenozoic Tethys Sea • Shells of these larger forms accumulated • to form thick limestones, • some of which ancient Egyptians used • to construct the Sphinx and the Pyramids of Giza

19. Cenozoic Foraminifera • Benthonic foraminifera of the Cenozoic Era • Cibicides americanus • Early Miocene, California

20. Cenozoic Foraminifera • A planktonic form • Globigerinoides fistulosus • Pleistocene, • South Pacific Ocean

21. Cenozoic Foraminifera • The numerous disc-shaped objects are Nummulites, • a benthonic foraminifera in the limestone • used to construct the pyramids on the Giza Plateau, Egypt

22. Corals—Reef Builders Again • Corals were perhaps the main beneficiary • of the Mesozoic extinctions • Having relinquished their reef-building role • to rudists during the mid-Cretaceous, • corals again became the dominant reef builders • They formed extensive reefs • in the warm waters of the Cenozoic oceans • and were especially prolific in the Caribbean • and Indo-Pacific regions

23. Coral • The dominant reef-building animals • of the Cenozoic Era are corals • such as this modern colonial scleractinian

24. Other Suspension Feeders • Other suspension feeders • such as bryozoans and crinoids • were also abundant and successful • during the Paleogene and Neogene • Bryozoans, in particular, were very abundant • Perhaps the least important • of the Cenozoic marine invertebrates • were brachiopods, • with fewer than 60 genera surviving today • Brachiopods never recovered • from their reduction at the end of the Paleozoic

25. Mollusks • Just as during the Mesozoic, • bivalves and gastropods • were two of the major groups • of marine invertebrates during the Cenozoic, • and they had a markedly modern appearance • After the extinction of ammonites and belemnites • at the end of the Cretaceous, • the Cenozoic cephalopod fauna • consisted of nautiloids and shell-less cephalopods • such as squids and octopuses

26. Bivalves • encrusted with barnacles • from the Miocene of Virginia • The bivalve Chlamya sp.

27. Gastropods • from Pliocene rocks in Florica • The gastropod Busycon contrarium

28. Echinoids • in the infaunal habitat • and were particularly prolific • during the Cenozoic • Echinoids continued their expansion • New forms such as this sand dollar • evolved during this time • from biscuit-shaped ancestors

29. Cenozoic Vegetation and Climate • Angiosperms continued to diversify • during the Cenozoic • as more and more familiar types of plants evolved • although seedless vascular plants and gymnosperms were also present in large numbers • In fact, many Paleogene plants • would be familiar to us today • but their geographic distribution was not • what it is now because changing climatic conditions • along with shifting plant distributions were occurring

30. Changing Climatic Patterns • Climate was a strong control • on plant distribution in the past • Furthermore, leaves with entire or smooth margins, • many with pointed drip-tips, • are dominant in areas with abundant rainfall • and high annual temperatures • Smaller leaves with incised margins • are more typical of cooler, drier areas

31. Leaf Structure • For instance, leaves with entire or smooth margins, • many with pointed drip-tips, • are found mostly in areas with abundant rainfall • and high annual temperatures • Smaller leaves with incised margins • are more typical of cooler, drier areas

32. Plant Leaves as Climatic Indicators • Fossil floras with mostly • smooth-margined leaves with drip-tips • indicate warm, wet conditions • while predominance of small leaves • with incised margins and no drip-tips • indicate a cool, dry climate

33. Paleocene Flora • Paleocene rocks in the western interior of North America • have fossil ferns and palms, • both indicating a warm, subtropical climate • In a Paleocene flora in Colorado • with about 100 species of trees, • nearly 70 percent of the leaves • are smooth margined and many have drip-tips • This nature of these leaves • coupled with the diversity of plants • is much like that in today’s rain forests • Early Oligocene fossil plants indicate • that a warm, wet climate persisted then

34. Late Paleocene Thermal Maximum • Seafloor sediments and geochemical evidence • indicate that about 55 million years ago • an abrupt warming trend took place • During this time, • known as the Paleocene-Eocene Thermal Maximum, • large-scale oceanic circulation was disrupted • so that heat transfer from equatorial regions • to the poles diminished or ceased • As a result, • deep oceanic water became warmer, • resulting in extinctions • of many deep-water foraminifera

35. Release of Methane • Some scientists think • that this deep, warm oceanic water • released methane • from seafloor methane hydrates, • contributing a greenhouse gas • to the atmosphere • and either causing or contributing • to the temperature increase at this time

36. Subtropical Conditions • Subtropical conditions persisted • into the Eocene in North America, • probably the warmest of all the Cenozoic epochs • Fossil plants in the Eocene John Day Beds in Oregon • include ferns, figs, and laurels, • all of which today live in much more humid regions, • as in parts of Mexico and Central America

37. Warm Eocene Climate • Yellowstone National Park in Wyoming • has a temperate climate now • with warm dry summers and cold snowy winters, • certainly not an area where one would expect • avocado, magnolia, and laurel trees to grow • Yet their presence there • during the Eocene indicates the area then • had a considerably warmer climate • than it does now

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

39. Climatic Change • Since the Oligocene, • mean annual temperatures • have varied somewhat worldwide, • but overall have not changed much • in the middle latitudes except • during the Pleistocene Epoch

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

41. Herbivores Adapted Quickly • Many herbivorous mammals • quickly adapted to these new conditions • by developing chewing teeth suitable • for a diet of grass

42. Cenozoic Birds • Birds today are diverse and numerous, • making them the most easily observed vertebrates • But the first members • of many of the living orders, including • owls, hawks, ducks, penguins, and vultures, • evolved during the Paleogene • Beginning during the Miocene • a marked increase in the variety of songbirds • took place, and by 5 to 10 million years ago • many of the existing genera of birds were present

43. Recently Birds’ Diversity Decreased • Birds adapted to numerous habitats • and continued to diversify into the Pleistocene, • but since then their diversity • has decreased slightly

44. Birds Vary Considerably • Today, birds vary considerably • in habitat, adaptations, and size • Nevertheless, their basic skeletal structure • has remained remarkably constant • throughout the Cenozoic

45. Adaptations for Flying • Given that birds evolved from a creature very much like Archaeopteryx • this uniformity is not surprising • because adaptations for flying • limit variations in structure

46. Other Adaptations • Penguins adapted to an aquatic environment, • and in some large extinct and living flightless birds • the skeleton became robust • and the wings shrank to vestiges • Many authorities on prehistoric life are now convinced • that birds are so closely related to dinosaurs • that they refer to them as avian dinosaurs • In fact, following the demise of the non-avian dinosaurs • at the end of the Mesozoic, • the dominant large, land-dwelling predators • during the Paleocene and well into the Eocene • were flightless birds

47. Diatryma • Among these predators were giants • such as Diatryma • This remarkable bird stood more than 2 m tall, • had a huge head and beak, toes with large claws, • and small vestigial wings

48. Diatryma and Related Genera • Its massive, short legs • indicate that Diatryma was not very fast, • but neither were the early mammals it preyed on • This extraordinary bird and related genera • were widespread in North America and Europe • and in South America • they were the dominant predators • until replaced by carnivorous mammals • during the Oligocene Epoch

49. Moas and Elephant Birds • Two of the most notable large flightless birds • were the now extinct moas of New Zealand • and elephant birds of Madagascar • Moas were up to 3 m tall, • elephant birds were shorter • but more massive, weighing up to 500 kg • They are known only • from Pleistocene-age deposits, • and both went extinct shortly after • humans occupied their respective areas

50. Fliers • Large flightless birds are truly remarkable creatures, • but the real success among birds belongs to the fliers • Even though few skeletal modifications • occurred during the Cenozoic, • a bewildering array of adaptive types arose • If number of species and habitats occupied • is any measure of success, • birds have certainly been • at least as successful as mammals