Eocene-Oligocene 1
- paradise lost Jarðsaga 2
- Saga Lífs og Jarðar Ólafur Ingólfsson
Háskóli Íslands
Climate started cooling
towards the end of Eocene
Global climate during the Late Eocene was still warm, but
on a cooling trend. Glaciers begun to form in Antarctica.
Oligocene (“almost recent”)
• The Oligocene is the third epoch of the Cenozoic, 34 -23
MY.
• Global cooling marked the start of the Oligocene, an
environmental shift that led to changes in the flora and
fauna. Global temperature dropped as much as 10° C,
shrinking forests and introducing the grassy plains that
would come to dominate in the Miocene.
•Herbivorous species adapted to eating grass and
carnivores adapted to hunting out in the open. Both groups
evolved better eyesight to see predators and prey as well
as elongated limbs to increase speed over open terrain.
• During this epoch archaic species of the early Cenozoic
were replaced by modern herbivores, such as horses,
camels and deer, and carnivores such as cats and dogs.
Oligocene World
Oligocene Ocean Currents
When Antarctica became isolated in a South Pole position, the coastal
seas of Antarctica began to freeze, changing the ocean currents
dramatically. Cold water and icebergs flowed north. Warm currents
circulated around the equatorial continents.
Oligocene climate
During the Oligocene, glacial ice covered the South Pole but
not the North Pole. Seasonal sea ice may have formed
there. Increased pole-equator temperature gradients.
Oxygen
isotope
records show
cooling and
growth of
glaciers
Mammals go
marine
Whales evolved and
diversified during the
Eocene and Oligocene,
and the two groups of
Mysticetes (“skíðhvalir”) and Odontocetes (“tannhvalir”)
originated between
40-35 MY ago
Mesonychide – ancestors
of whales and hippos
Whales evolved from wolf-like creatures which 60-55
MY ago began searching for food in the water.
Andrewsarchus, the biggest mesonychid,
has a skull of about 83cm which would
make it about 1.8m high and 5m long the largest meat-eating land mammal
ever.
Lived in Asia, Europe and America. The Mesonychians
were a group of carnivorous hoofed animals. These
animals might have been solitary hunters/scavengers
along river banks and tide lines.
http://www.visindavefur.hi.is/svar.asp?id=3556
http://www.pbs.org/wgbh/evolution/library/03/4/quicktime/l_034_05.html
Archaeocetes: Early Whales,
Dolphins/Porpoises
Six families (ættir) of cetaceans
(hvalir) are commonly included in
Archaeocetes (fornhvalir):
These archaeocete families
document that the Eocene
- Pakicetidae
cetacean evolution is
- Ambulocetidae
characterized by increasing
- Remingtonocetidae
aquatic adaptations, starting
- Protocetidae
at amphibious early whales
- Basilosauridae
(pakicetids, ambulocetids) to
more marine protocetids
- Dorudontidae
(frumhvalir).
Pakicetidae
- Early-to-middle Eocene, ca. 50 MY ago, in India and
Pakistan. Fossils found in fresh-water deposits, most
represent shallow streams in arid climate
- Although pakicetids were land mammals, they are
related to whales and dolphins based on a number of
specializations of the ear.
Skeletons of Pakicetus and Ichthyolestes
- Dozens of fossils known, but none consist of complete
skeletons. Mostly skulls, teeth, and jaw fragments.
How do we know this animal was
“a whale”?
A 50 million year old earbone of
Pakicetus lies between poppy
seeds that show its tiny size.
Photo taken with a scanning
electron microscope.
The hearing organ of Eocene whales was not specialized as that of modern cetaceans. Instead it
represents a compromise of adaptations relating
to underwater sound reception and a hearing
system used for listening to sounds in air.
Ambulocetidae
- Known from Eocene (49 MY) rocks in northern India
and Pakistan
- Fewer than 10 described fossils; one nearly
complete skeleton (Ambulocetus natans).
- A. natans skeleton suggest it was probably slow on
land and an ambush hunter which attacks prey in or
near shallow water (like modern crocodiles).
- Only known from nearshore marine environments,
including bays and estuaries.
Ambulocetidae
in action
Copyright Carl Buell
Remingtoncetidae
Illustration by Carl Buell and taken from
http://www.neoucom.edu/Depts/Anat/Remi.html.
- Only known from India and Pakistan, ca 46-43 MY
(middle Eocene). It was a small animal, no bigger than a
river otter.
- Dozens of fossils described, most document
morphology of skull and lower jaw
- Most fossils known from marine, nearshore deposits;
may have lived in bays and saltwater swamps
Birthplace of
whales: The
Tethys Seaway
Protocetidae
Some protocetids were probably the ancestor of all later
cetaceans (including the modern groups). They are the
first whales found outside of Indo-Pakistan, and are
known from Africa and North America. Protocetids are
only found in sediments deposited in shallow seas.
Protocetids were the first whale group to develop tail
flukes and most were probably agile and quick aquatic
hunters who preyed on small animals.Their teeth were
reduced and most prey was probably swallowed whole.
Protocetidae
- frumhvalir An artist's rendering of a
largely aquatic early
whale of the genus Rodhocetus. This mammal,
which was the size of a
sea lion, lived near the
shores of the Tethys
Sea, between Asia and
the South Asian subcontinent, about 47 MY
ago. J. Klausmeyer
/Science
http://www.pbs.org/wgbh/evolution/library/03/4/quicktime/l_034_05.html
Basilosauridae (“king Lizzard”)
Reconstruction of Basilosaurus cetoides .From:
http://darla.neoucom.edu/DEPTS/ANAT/BasilAndDor.htm
A Carnivorous early whale - ate fish,
sharks and molluscs. It was huge, 1518 m long. This Eocene whale (40-36
MY ago) is well known from a large
number of fossils. It must have been
common in the warm shallow sea
between Africa and Europe, and
around North America.
Basilosaurus
The narrow skull contained 44 teeth of various shapes:
pointed, conical teeth in front, and saw-edged teeth in
the back. This configuration made it possible for Basilosaurus to catch and eat fish, hard-shelled mollusks, and
crustaceans. One fossil had a ball of fish and sharks
inside it, the remains of its last meal. The skeletons also
show a pair of tiny legs.
Dorudontidae (“spear-toothed”)
Basilosaurids and Dorudontids lived at
the same time, and fossils are mainly
known from the eastern USA and from
Egypt (but were probably worldwide in
their distribution). While Basilosaurids
had snake-like bodies, with a tail fluke,
Dorudontids were proportionally more
like dolphins.
An Eocene killer Whale
The Dorudontides were carnivorous, ate fish and molluscs.
They were ca 5 m long. A famous fossil locality in Egypt
has preserved many of them in ancient shallow-bay sediments, along with their babies. Perhaps they calved in bays
for protection like some modern whales.
Family tree of Whales
Not only whales grew large and
vicious...
Tropical rainforests withdraw towards
the equatorial regins; conifers and later
grasslands/steppes expand at higher
latitudes
Coling and shrinking tropical
forests towards
the end of the
Eocene opened up
the landscape.
This created
space for larger
herbivores and,
consequently,
larger carnivores
Oligocene vegetation
• By the Oligocene the major evolution and
dispersal of modern types of angiosperms had
occurred.
•The vegetation of the higher latitudes in the
northern hemisphere changed from tropical
evergreen forest such as had typified the
Eocene, to a temperate deciduous woodland of
evergreen and broad-leaved trees.
• Grasses, which appeared for the first time as
plants of water margins in the Eocene, became
more common in open habitats.
Laurasian fauna
Herds of large, herbivorous
(shrubs, tree branches, soft
vegetation) brontotheres
(“Thunder beast”) lived on the
N American and Asian plains.
The brontotheres were
common and widespread
40 MY ago, when warm
forests were opening
into drier plains. They
are related to rhinos,
tapirs and horses.
Indricothere (“indrik beast”)
The indricotheres (30-25 MY) were huge herbivores browsing on upper branches of deciduous trees. Their
closest living relatives are the Rhinos. The largest males
were 4.5m at the shoulder, weighing 15 tonnes.
The largest land mammals – ever!
Indricotheres were
the largest land
mammals ever to live.
The indricotheres had very large nasal passages meaning
they had a very good sense of smell. They were related to
the Rhinoceros, but browsed the tops of trees like a
giraffe.
Another strange giant...
...the Chaligotherium
(“pebble beast”), 453 MY.
Chalicotheres had the face of a horse, the neck of
an ox, the arms and shoulders of a massive ape,
the front claws of an anteater and short rear legs
to support its massive bulk.
A Tertiary “Panda”
Fossils of a Chalicotherium
are found in the Oligocene
of Asia, but fossils are rare.
They had no front teeth in
the upper jaw, and even the
back teeth show little wear
from use. They must have
been fussy eaters – picking
only the freshest shoots
and putting them straight
into the back of their
mouths like modern pandas.
Hebivorous - Soft shoots
only, thank you!
Closest living relatives are
Rhinos, tapirs and horses
http://www.pbs.org/wgbh/evolution/library/03/4/quicktime/l_034_04.html
References used for this lecture
Stanley: Earth System History. Arnold, London
Fortey: Life. A Natural History of the First Four Billion Years on Earth. Vintage, New York.
http://www.sci.tamucc.edu/tmmsn/extinct/archaeocetes.html
http://www.cetaceen.de/images/zeichnungen/EvolutionWale.png
http://www1.thdo.bbc.co.uk/beasts/factfiles/index_all.shtml
http://www.palaeos.com/Vertebrates/Units/520Cetartiodactyla/520.120.html#Georgiacetus
http://www.sciencenews.org/20010922/fob1.asp
http://www.kokogiak.com/megafauna/strange.asp
http://darla.neoucom.edu/DEPTS/ANAT/BasilAndDor.htm
http://www.pbs.org/wgbh/evolution/library/03/4/quicktime/l_034_05.html
http://www.ucmp.berkeley.edu/mammal/eutheria/creodonta.html
http://www.flmnh.ufl.edu/natsci/vertpaleo/fhc/mesoh1.htm
http://www.copyrightexpired.com/earlyimage/prehistoriclifeafterkt/index.html
http://www.ucmp.berkeley.edu/tertiary/oli/olilife.html
http://www.clas.ufl.edu/users/emartin/GLY3074S03/lecturenotes/cenozoicclimate.htm
http://www.palaeoentomolog.ru/Publ/PALJ153.pdf
http://www.pbs.org/wgbh/evolution/library/03/4/quicktime/l_034_04.html
http://www.nature-source.com/turtles.htm
http://sorcerer.ucsd.edu/tauxe/pdfs/shackleton00.pdf