Paleogene

Lecture 25

Copyright © 2012 Joe Marx.

Cenozoic Era• Third of the three eras

that comprise the Phanerozoic.– From 65 mya to now.

• Named for its “new life”—recognizably modern.– Often called “The Age of

Mammals.”• Noted for the movement

of the modern continents into their current positions.

Paleogene Image courtesy of U.S. Geological Survey. Page 2

Paleogene Period• The first of the two Cenozoic periods.

– Began 65 mya with the end-Cretaceous extinction and ended—somewhat arbitrarily—23 mya.

– Subdivided into three epochs:• Paleocene, Eocene and Oligocene.

– The name means “ancient born,” due to changes in European marine fossils from the Paleogene to the Neogene.

• Highlights:– Mammals and angiosperms dominated

the land, while whales and sharks dominated the sea.

• All of today’s continents existed but generally lay closer together than now.

Paleogene Image courtesy of Wikipedia. Page 3

The Paleogene Environment• The atmospheric O2 content declined from about

130% to about 100% of current levels, while CO2 content was about twice that of today.

• The mean surface temperature, at 62° F, was about four degrees warmer than today’s.– Climates heated up considerably at the start of the

period but then became steadily cooler and drier.• Sea levels remained relatively high throughout

the period.– Epicontinental seas were widespread.

• Calcite seas shifted to aragonite seas at the end of the Eocene, enabling large modern coral reefs to form.

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Paleogene Marine Life• Populated, as they are today, by the survivors of

the end-Cretaceous extinction:– Benthic and planktonic foraminifera—protozoa that

secrete calcium carbonate tests.– Calcareous nannoplankton and diatoms—plant-like

protists encased in carbonate and silica tests.– Dinoflagellates, which are cyst-producing protists,

half of which are plant-like, half animal-like.– Hexacorals.– Bryozoans.– Sea urchins.– Crabs, snails and bivalves.– Teleosts, sharks and whales.

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Whales• Descendants of even-toed hoofed mammals that

moved from the land to the sea.– First adapted to the sea during the Early Eocene,

about 50 mya, becoming fully aquatic by 40 mya.– The top marine predators by the Late Eocene.

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Indohyus, a raccoon-sized mammal of the Middle Eocene possibly ancestral to

whales. Indohyus was adapted to aquatic life although it fed on land plants.

Left-hand image courtesy of Frederic Hilpert.Right-hand image courtesy of Pavel Riha.

Rhodocetus, a Middle Eocene aquatic predator that had

characteristics of both hoofed mammals and whales.

Image courtesy of Virginia Museum of Natural History and Karen Carr.

Sharks• Throughout the Paleogene, modern-type sharks

evolved and flourished as marine predators.

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C. megalodon pursuing two early baleen whales, each 35 feet long.

– Toward the end of the Paleogene, huge sharks joined whales at the top of the food web.• The largest, C. megalodon,

was among the biggest and most powerful predators ever.

– Megalodon lived 25 to 1.5 mya.

– The largest specimens are estimated to have been 67 feet long and to have weighed 114 tons.

Image courtesy of Nobu Tamura.

• The Paleogene saw the rise and spread of two important new marine lifestyles: – A pair of existing groups expanded onto sand:

• Bivalves, which had previously avoided sandy areas.• Sand dollars, which are flattened, burrowing sea urchins

that live atop or just beneath sandy or muddy substrates.– A– A new type of bird took emerged

as flightless divers:• The penguin lineage originated

near the end-Cretaceous, although the earliest penguins could still fly.

• The oldest known flightless penguin is Waimanu from Paleocene New Zealand.

New Marine Life Styles

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Waimanu manneringi.

Angiosperms• The dominant land flora during the Paleogene.

– Flowering plants first replaced cycads and ferns in the understory, and then conifers in the canopy.• About half of the modern genera of flowering plants had

developed by Oligocene time.– Grasses, a new kind of flowering plant, became

prominent by the end of the Paleogene.• The grass family originated near the end of the

Cretaceous.– The last major group of plants to evolve.– Confined at first to wooded or swampy areas.

• The continuous growth of grass leaves from the base evolved in the Late Oligocene, when ecosystems dominated by grasses first appeared.

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Image courtesy of Wikimedia Commons.

Paleogene Birds• Most Paleogene birds were

large and lived near water.– A good example is

Presbyornis, a genus in the early lineage of ducks, geese and swans:• Lived during the Paleocene and

Eocene.• Was the size and shape of a

goose but with longer legs.• Lived in colonies around shallow

lakes.• Filtered small plants and animals

from the water with its broad, flat bill.

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Reconstruction of Presbyornis pervetus.

Gastornis• A large flightless bird, often called

Diatryma, that lived during the Late Paleocene and Eocene.– Grew up 6½ feet tall.– Had a huge beak with a slightly

hooked top, and powerful legs with big, taloned feet.

– May have been carnivorous, although the fossil evidence is not conclusive.• Often pictured devouring ancestral

horses.• Modern birds of its size feed on plants

and small animals.

Paleogene Page 11Upper image courtesy of Monika Betley.Lower image courtesy of Wikimedia Commons.

Mammal Evolution• In a remarkable adaptive radiation, most modern

orders of mammal appeared relatively quickly in the Late Paleocene and Early Eocene.– The new mammals included:

• Carnivora.• Bats.• Primates.• Rodents.• Rabbits.• Even-toed ungulates (pigs, deer, camels, goats and

cattle).• Whales.• Elephants and their extinct relatives.• Odd-toed ungulates (horses, tapirs and rhinoceroses).

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Paleocene Mammals• Following the end-Cretaceous mass extinction,

mammals became the dominant fauna on land.– Mammals remained relatively small and archaic for

most of the Paleocene.• By the end of the epoch, however, they were diversifying

into all the niches vacated by the non-avian dinosaurs.

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Titanoides primaevus was a rhinoceros-sized Paleocene

herbivore.

Skull and restoration of Ptilodus, a squirrel-sized Paleocene multituberculate. The latter, now extinct, were

rodent-like mammals that gnawed on seeds and nuts.

Left-hand image courtesy of Dmitry Bogdanov. Middle image courtesy of Nobu Tamura.Right-hand image from Scott, W.B., A History of Land Mammals in the Western Hemisphere, 1913.

Eocene Mammals• Most Eocene mammals were relatively small.

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Early Eocene Hyracotherium, the oldest ancestor of horses, about two feet long.

Icaronycteris index, Early Eocene bat, about

six inches long.

Moeritherium, Late Eocene relative of elephants, about three feet tall.

A pair of 1½ feet tall Diacodexis pakistanensis, the oldest known even-toed ungulate, confronted by a Pakicetus inachus, a direct ancestor of whales, during the

Early Eocene.

Images courtesy of Wikimedia Commons.

Mesonychids• An extinct order of

medium to large-sized even-toed carnivorous ungulates.– “Wolves on hooves.”– Diversified through

the Paleocene and Eocene, but became extinct in the Early Oligocene.• The dominant

terrestrial predators during the Paleocene and Eocene.

PaleogeneUpper image courtesy of Stanton Fink.

Lower image courtesy of Wikimedia Commons. Page 15

Hapalodectes serus, a Middle Eocene mesonychid from Mongolia.

Andrewsarchus mongoliensis, an Eocene mesonychid from Mongolia. Eleven feet long and six feet tall, it may have been the largest

carnivorous mammal ever to exist.

Brontotheres• An Eocene family of odd-toed ungulates.

– Started small but evolved to massive size before going extinct.

– Browsing animals that may have lived in herds.

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Megacerops, a Late Eocene brontothere, was sixteen feet long and weighed two tons.

Left-hand image courtesy of Dimitry Bogdanov.Right-hand image courtesy of Stanton Fink.

Embolotherium andrewsi, a Late Eocene brontothere, was

about eight feet tall.

Early Primates• The primate lineage probably originated in the

Middle or Late Cretaceous.– Its nearest relatives are rodents and rabbits. – The oldest known primate fossil is Late Paleocene.– Primates diversified as tree and shrub dwellers

throughout the Paleogene.

PaleogeneLeft-hand image courtesy of Nobu Tamura.

Right-hand image courtesy of Wikimedia Commons. Page 17

Early Eocene Smilodectes gracilis. Note the hands and feet.

Reconstruction of Late Paleocene Plesiadapis, the oldest known

fossilized primate.

Image courtesy of American Museum of Natural History.

Oligocene Mammals• During the Oligocene, mammals grew larger and

evolved closer to modern forms:– The species of even-toed ungulates, like deer, pigs

and antelopes, began to outnumber the species of odd-toed ungulates, like horses and rhinos.

– Elephants became larger and acquired their trunks and tusks.

– Modern carnivores expanded, including dogs, cats and weasels.

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Image courtesy of Dimitry Bogdanov.

Paraceratherium• A gigantic hornless Oligocene rhinoceros, the

largest land mammal known.– About 39 feet in length and 26 feet high with the

head raised.– Browser that lived on the leaves and twigs of trees

and large shrubs.

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Aegyptopithecus• An ancestor of Old World monkeys and apes.

– Lived during the Late Eocene and Early Oligocene.– Probably an arboreal quadruped that fed on fruit.– About one foot long, it was arboreal and slow-

moving.

PaleogeneLeft-hand image courtesy of Nobu Tamura.

Right-hand image courtesy of Wikimedia Commons. Page 20

Reconstruction of Aegyptopithecus zeuxis. Reconstruction of head of A.zeuxis.

Eocene Paleogeography• India was starting to

collide with Asia.• Australia had rifted

from Antarctica.• The East Pacific Rise

extended the length of the Americas.

• Seaways separated the northern from the southern continents, and Europe from Asia.

• Europe and Greenland had rifted, joining the Arctic to the Atlantic.

• A Bering land bridge connected North America with Asia.

Paleogene Page 21Image courtesy of C.R. Scotese, http://www.scotese.com (PALEOMAP website).

Paleogene Climate• Began notably warm but then cooled steadily.

– The Paleocene was much warmer than today.• Palm trees grew in Greenland and Patagonia.

– An abrupt shift in 13C and 18O ratios in deep-sea forams mark a Paleocene-Eocene warming pulse.• Methane release may have boosted the change.

– The Early Eocene was the warmest interval of the Cenozoic.• Alligators and redwoods thrived near the North Pole.

– The rest of the Eocene saw progressive cooling, but climates were still warm compared to today.

– The Oligocene was slightly warmer than today.• For the first time, ice covered much of Antarctica.

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Early Eocene Climate• Average global temperatures were about 11° F

hotter than today.– England was covered with a tropical jungle.– Primates, ungulates, opossums and palm trees

migrated across the Bering land bridge to North America.

• The extended warmth was likely due to a nearly complete coverage of land surfaces by forest:– Evaporated and transpired water vapor acted as a

greenhouse gas, trapping the Sun’s heat.– Thick clouds carried warmth from the Equator to

the poles.

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Early Eocene Arctic• Ellesmere Island had a diverse subtropical biota

of terrestrial plants and vertebrates.– Coastal areas near the pole were warm, humid and

swampy, like today’s eastern North Carolina, with ancestral cypresses, redwoods and sycamores.

Paleogene Page 24Left-hand image courtesy of American Museum of Natural History.

Right-hand image courtesy of NASA.

Museum diorama of an Ellesmere Island summer scene during the Early Eocene.

A summer scene on today’s Ellesmere Island, about 690 miles from the North Pole.

Image courtesy of David Pape.

The Southern Ice Cap• Climatic change marked the end of the Eocene.

– A Circumpolar Current formed as soon as Australia and South America had rifted from Antarctica.• T

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• The powerful west-to-east current blocked warm water and air from moving southward.

• Cold, dense water trapped in the current sank, forming a deep frigid layer that cooled the surface water.

• Reduced oceanic evaporation then cooled and dried climates worldwide, particularly in Antarctica.

• The modern glacial age began about 34 mya, when a massive glacier gradually covered all of Antarctica.

Images courtesy of U.S. Geological Survey.

Laramide Orogeny• The third deformational episode in the evolution

of the North American Cordillera.– Lasted from the Late Cretaceous to the Eocene.– Caused by subduction along the Pacific coast.

• Arc volcanism and eastward folding and thrusting occurred from Idaho northward and Arizona southward.

• In between, the inland Precambrian basement was elevated from Montana to New Mexico.

– Caused by an extremely shallow angle of subduction.

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◄ Lewis thrust at Altyn Peak, Glacier NP, Montana. The tree line marks the

fault trace.

“Buoyant” or “flat slab” subduction.►

Image courtesy of Wikimedia Commons.

Laramide Uplifts and Basins• Nearly overlap the modern central and southern

Rockies, which are post-Laramide.– Possibly caused by a slight clockwise rotation of

the Colorado Plateau, which remained rigid.– Most of the uplifts were anticlines bounded by

steeply dipping thrust faults.

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◄ The Big Horn Mountains (background) and the Powder River Basin (foreground) originated as a Laramide uplift and basin.

Green River Formation• The world’s most extensive lacustrine deposits.

– Amassed during six million years of the Eocene.– Three Laramide intermontane basins were filled

with thin, cyclic layers of sediment.– The formation is noted for plant and animal fossils,

as well as the world’s largest oil shale deposits.

Paleogene Page 28Images courtesy of The Virtual Fossil Museum, www.fossilmuseum.net.

Surface outcrop area of the Green River Formation. Fossil bat from the

Green River Formation.Fossil palm frond from the

Green River Formation.

Olympic Mountains• An accretionary wedge of ocean-floor sediments

and pillow lavas piled into a Pacific embayment.– Primarily Eocene sandstones, turbidites and

basalts.

Paleogene Left-hand image courtesy of Ron Blakey, Northern Arizona University.Right-hand image courtesy of Wikimedia Commons.

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Mid-Eocene North America showing the embayment in

which the Olympics formed.

►

Mount Olympus, Olympic National Park, Washington.

Image courtesy of Wikimedia Commons.

Mississippi Embayment• A structural basin, up to 1½ miles deep, filled

mostly with Paleogene sediment.– Slices through the Alleghenian-Ouachita orogen.– M

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– Most likely mode of origin: • About 95 mya, during the Cretaceous,

the region passed over the Bermuda hotspot, then unusually active.

• Upwelling and thermal swelling lifted the crust by as much as 10,000 feet.

• The uplift eroded rapidly and, when the hotspot moved on, the cooling crust subsided into a trough that was flooded by the Gulf of Mexico.

• The Mississippi and other streams turned toward the trough and filled it.

Images courtesy of U.S Geological Survey.

Chesapeake Bay Impact Crater• Formed by a bolide that struck NE of Norfolk,

Virginia, in the Late Eocene, about 36 mya.

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– The largest impact crater in the U.S. and the 6th-largest on Earth.

– The bolide was 2 to 3 miles wide.– The crater, now buried under

younger sediments, is 85 miles wide and about seven miles deep.

– The impact incinerated everything within hundreds of miles and triggered gigantic tsunamis.• The bolide may have been part of an

extended comet shower that triggered an end-Eocene extinction.