Life of the Cenozoic Era

Chapter 18 Life of the Cenozoic Era

Among the diverse Pliocene and Pleistocene • mammals of Florida were • 6 m long giant ground sloths • and armored mammals known as glypotodonts • that weighed more than 2 metric tons

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

Geologically Short • Although the Cenozoic • constitutes only 1.4% of all geologic time, • this comparatively brief episode • of 66 million years of Earth and life history • was brief only in the context of geologic time • From the human perspective • it was far longer than we can even conceive, • certainly long enough for many changes • to take place in Earth's biota

Evolution of Mammals • 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.

Other Biological Events • Other equally important biological events • were taking place • For instance, angiosperms • continued to dominate land plant communities • and now constitute more than 90% of all land plants • Birds evolved during the Jurassic, • perhaps earlier, 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

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 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.

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 in Nebraska, • Badlands National Park in South Dakota, • and John Day Fossil Beds National Monument in Oregon.

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

Eastern Mammal Fossils • Deposits with land-dwelling fossil mammals • are not nearly as common in the eastern part of the continent, • but Florida is a notable exception. • Furthermore, 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.

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. • Some of these fossil are truly remarkable • because even hair, feathers, and color • have been preserved.

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 invertebrates • were the foraminifera, radiolarians, corals, • bryozoans, mollusks, and echinoids

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 • Entire families of phytoplankton • became extinct at the end of the Cretaceous

Species Diversified • Only a few species in each major group • survived 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

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 • is present in several western States

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

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

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

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

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

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

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

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

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

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

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

Cenozoic Vegetation and Climate • During the Cenozoic, • Angiosperms, or flowering plants, • continued their diversification • 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 quite familiar to us today, • but their geographic distribution was very different

Changing Climatic Patterns • Changing climatic patterns • accompanied by shifting plant distributions • were occurring in the Cenozoic • The makeup of ancient floras • and the types of leaves • are good climatic indicators. • Some plants today are confined to the tropics, • whereas others have adapted to drier conditions

Leaf Structure • Leaf structure is a good climatic indicator • 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

Plant leaves as Climatic Indicators • Fossil floras with mostly • smooth-margined leaves with drip-tips • indicate the climate • was wet and warm • while small leaves with incised margins • indicate a cool, dry climate

Paleocene Flora • Paleocene rocks • in North America's western interior • have fossil ferns and palms, • both indicating a warm subtropical climate • In a recently discovered Paleocene flora • in Colorado • with about 100 species of trees, • nearly 70 percent of the leaves • had smooth margins and many had drip tips • This range of diversity is much like • that found in today's rain forests

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

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 encouraging • the temperature increase at this time

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 only in • the humid parts of Mexico and Central America

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 • had a considerably warmer climate • than it does now

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

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

Decrease in Precipitation • A general decrease in precipitation • over 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 savanna conditions • grasslands with scattered trees • and finally to steppe environments • short-grass prairie of the desert margin

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

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

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

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

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

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 • One early adaptation involved the evolution • of large, flightless predatory birds • 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

Diatryma • Restoration of Diatryma, • which lived during the Paleocene and Eocene • in North America and Europe

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 • during the Paleogene, • and in South America • they were the dominant predators • until about 25 million years ago • Eventually, they died out, • being replaced by carnivorous mammals

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, • whereas 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

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

The Age of Mammals Begins • Mammals coexisted with dinosaurs • for more than 140 million years, • yet during this entire time • they were neither abundant nor diverse, • and even the largest was only about 1 m long • Even at the end of the Cretaceous Period • only a few families of mammals existed, • a situation that was soon to change

Mammal Diversification • With the demise of dinosaurs and their relatives, • mammals quickly exploited the adaptive opportunities, • beginning a remarkable diversification • that continued throughout the Cenozoic Era • The Age of Mammals had begun

Life of the Cenozoic Era

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