Setting the Stage The Mesozoic Era is the Age of the Dinosaurs
and lasted almost 180 million years from approximately 250 to 65
mya. This era includes 3 well known periods called the Triassic,
Jurassic, and Cretaceous periods. A mass-extinction marked the
beginning and end of the Mesozoic Era. The event that caused the
transition from the Paleozoic era to the Mesozoic era, The Permian
Extinction was the greatest extinction this earth has seen. This
extinction wiped out about 95% of all marine life and 70% of
land-life. This allowed the dinosaurs to diversify and enter niches
left unoccupied by the Permian Extinction. The era ended with "The
Great Extinction" which marked the end of the dinosaurs as the
Cenozoic era began.
Slide 3
Arrangement of Continents At the beginning of the Mesozoic, all
of the world's continents were combined into the supercontinent of
Pangaea, which rifted into Laurasia in the north and Gondwanaland
in the south. By the end of the era most of continents had
separated into their present form.
Slide 4
Estimated Global Temperatures in the Proterozoic Eon
Slide 5
Triassic During the Triassic, the Earth's land mass was a
single supercontinent called Pangaea ("all the land"). Pangaea was
surrounded by the world-ocean known as Panthalassa ("all the sea").
The global climate during the Triassic was mostly hot and dry, with
deserts spanning much of Pangaea's interior. However, the climate
shifted and became more humid as Pangaea began to drift apart. The
Earth's biosphere impoverished; it would take well into the middle
of the period for life to recover its former diversity. Therapsids
and archosaurs (reptiles) were the chief terrestrial vertebrates
during this time. Time 251 - 199 million years ago (Mesozoic
Era)
Slide 6
Triassic Biology The oceans teemed with the coiled- shelled
ammonites, mollusks, and sea urchins that survived the Permian
extinction and were quickly diversifying. The first corals
appeared, though other reef-building organisms were already
present. Giant reptiles such as the dolphin- shaped ichthyosaurs
and plesiosaurs preyed on fish and ancient squid. Pterosaurs, a
group of flying reptiles, took to the air. On firm ground, moss,
liverwort, and ferns carpeted forests of conifers, ginkgoes, and
palm-like cycads.
Slide 7
Triassic Biology - The First Mammals But perhaps the biggest
changes came with the evolution of dinosaurs and the first mammals
in the late Triassic, starting around 230 million years ago. One of
the earliest true mammals was the three-foot-long (one- meter-long)
Eozostrodon. The shrew-like creature laid eggs but fed its young
mother's milk - a monotreme like todays echidna or platypus. While
dinosaurs dominated many ecological niches, mammals remained small.
Therapsids - reptiles that had developed some mammalian
characteristics
Slide 8
Triassic Biology - The First Dinosaurs Among the first
dinosaurs was the two-footed carnivore Coelophysis, which grew up
to 9 feet (2.7 meters) tall, weighed up to a hundred pounds (45
kilograms), and probably fed on small reptiles and amphibians. It
showed up about 225 million years ago. A few million years later
came the 27.5-foot-long (8- meter-long) herbivore called
Plateosaurus.
Slide 9
Triassic Geology During the Triassic, almost all of the Earth's
land mass was combined into a single supercontinent called Pangaea
(All the Land) which straddled the equator From the east a vast
gulf entered Pangaea, the Tethys sea. Mean atmospheric O2 content
over period duration ca. 16 Vol % (80 % of modern level) Mean
atmospheric CO2 content over period duration ca. 1750 ppm (6 times
pre- industrial level) Mean surface temperature over period
duration ca. 17 C (3 C above modern level)
Slide 10
The End of the Triassic This period ended with another mass
extinction, followed by volcanic eruptions about 208-213 million
y.a. The suspected cause is global warming related to the increase
in volcanism. During this extinction, Pangaea began to break apart.
As a result of the extinction, 35% of all families died out.
Dinosaurs, however, survived and went on to dominate the
Jurassic.
Slide 11
Jurassic The Jurassic is named from the Jura Mountains of the
Alps. The Jurassic constitutes the middle period of the Mesozoic
Era. The start of the period is marked by the major Triassic
Jurassic extinction event. Two other small extinction events
occurred during the period Time 199 - 145 m.y.a (Mesozoic Era)
Slide 12
Jurassic Geology During the early Jurassic period, the
supercontinent Pangaea broke up into the northern supercontinent
Laurasia and the southern supercontinent Gondwana The Gulf of
Mexico opened in the new rift between North America and what is now
Mexico's Yucatan Peninsula. The Jurassic North Atlantic Ocean was
relatively narrow, while the South Atlantic did not open until the
following Cretaceous period, when Gondwana itself rifted
apart.
Slide 13
Jurassic Geology By subduction of the oceanic plates, mountains
began to form along the west coast of North America. Throughout the
Middle to Late Triassic, mountains continued to form along the
coast extending from Alaska to Chile. The Tethys Sea closed, and
the Neotethys basin appeared. Climates were warm, with no evidence
of glaciation. As in the Triassic, there was apparently no land
near either pole, and no extensive ice caps existed.
Slide 14
Jurassic Biology On land, the Triassic reptiles to one
dominated by dinosaurs alone. The first birds also appeared during
the Jurassic, having evolved from a branch of suarischian theropod
dinosaurs. Other major events include the appearance of the
earliest lizards, and the evolution of therian mammals, including
primitive placentals. Gymnosperms (plants with cones (Conifers))
appear.
Slide 15
Dinosaur Evolution Dinosaurs evolved along two lines - the
Ornithiscian or bird-hipped dinosaurs and the Saurischian or lizard
hipped dinosaurs. Predators such as Velociraptors and T. Rex, and
massive dinosaurs such as Brachiosaurs were Saurischians. Dinosaurs
such as Triceratops, Stegasaurus and horn-billed dinosaurs were
examples of Ornithischians Ironically, birds evolved from
Saurischians.
Slide 16
Jurassic Geology By the beginning of the Jurassic, Pangaea had
begun rifting into two landmasses, Laurasia to the north and
Gondwana to the south. This created more coastlines and shifted the
continental climate from dry to humid, and many of the arid deserts
of the Triassic were replaced by lush rainforests. Mean atmospheric
O2 content over period duration ca. 26 Vol % (130 % of modern
level) Mean atmospheric CO2 content over period duration ca. 1950
ppm (7 times pre- industrial level) Mean surface temperature over
period duration ca. 16.5 C (3 C above modern level)
Slide 17
Two Dinosaur Cladograms
Slide 18
Cretaceous The Cretaceous derived from the Latin "creta"
(chalk), usually abbreviated K for its German translation Kreide
(chalk). The Cretaceous is followed by the Cenozoic era. It is the
last period of the Mesozoic Era, and, spanning 79 million years,
the longest period of the Phanerozoic Eon. The Cretaceous was a
period with a relatively warm climate, resulting in high sea levels
and creating numerous shallow inland seas. This era was warm and
moist with excellent conditions for abundant life on land almost
from pole to pole. Extremely warm oceans may have lead to anoxic
conditions in deep water. (very low O2 levels toxic to marine life)
Time 145 - 65 million years ago (Mesozoic Era)
Slide 19
Cretaceous Biology The oceans and shallow inland seas were
populated with now-extinct marine reptiles, ammonites and rudists,
while dinosaurs continued to dominate on land. At the same time,
new groups of mammals and birds, as well as flowering plants,
appeared. Flowering plants (angiosperms) spread during this period,
although they did not become predominant until late in the
Cretaceous. The first representatives of many leafy trees appeared
in the Cretaceous.
Slide 20
Cretaceous Biology The evolution of plants was aided by the
appearance of bees; in fact angiosperms and insects are a good
example of coevolution. High oxygen levels produced giant insects.
However these may have gone extinct with the appearance of birds.
On land, mammals were a small and still relatively minor component
of the fauna. Early marsupial mammals evolved in the Early
Cretaceous, with true placentals emerging in the Late Cretaceous
period. An actual Velociraptor - much smaller, feathered compared
to the movie version
Slide 21
Cretaceous Dinosaurs Dinosaurs continue to diversify. Birds
evolve from the small therapod predators that we know as raptors.
These dinosaurs develop feathers (probably for insulation and
display) and gradually develop into gliders then fliers. The
Tyrannasaurus Rex appears in the late Cretaceous and exists until
the K-T extinction event.
Slide 22
Cretaceous Geology During the Cretaceous, the former
supercontinent of Pangaea completed its tectonic breakup into
present day continents, although their positions were substantially
different at the time. The Atlantic Ocean widened. Though Gondwana
was still intact in the beginning of the Cretaceous, it broke up
into South America, Antarctica and Australia rifted away from
Africa (though India and Madagascar remained attached to each
other)
Slide 23
Cretaceous Geology Thus, the South Atlantic and Indian Oceans
were newly formed. Such active rifting lifted great undersea
mountain chains along the welts, raising sea levels worldwide. To
the north of Africa the Tethys Sea continued to narrow. Broad
shallow seas advanced across central North America (the Western
Interior Seaway) and Europe, then receded late in the period,
leaving thick marine deposits sandwiched between coal beds. At the
peak of the Cretaceous, one-third of Earth's present land area was
submerged.
Slide 24
Cretaceous Geology During the Cretaceous Gondwana breaks into
South America, Antarctica, and Australia, Africa, India and
Madagascar. Laurasia breaks into North America, Europe and Asia.
The map of the Late Cretaceous shows most of todays continents.
Mean atmospheric O2 content over period duration ca. 30 Vol % (150
% of modern level) Mean atmospheric CO2 content over period
duration ca. 1700 ppm (6 times pre- industrial level) Mean surface
temperature over period duration ca. 18 C (4 C above modern
level)
Slide 25
The Cretaceous Extinction The K-T (Cretaceous - Tertiary)
extinction event is widely known as it marked the end of dinosaurs.
Two major geological upheavals occurred at this time approximately
65 million years ago - the volcanic event known as the Deccan Traps
flood basalts and the Chicxulub meteorite which struck the Yucatan
Peninsula in Mexico.
Slide 26
Deccan Traps The Deccan Traps formed between 60 and 68 million
years ago, at the end of the Cretaceous period. The major part of
this event occurs at the K-T boundary. This series of eruptions may
have lasted less than 30,000 years in total. The original area
covered by the lava flows is estimated to have been as large as 1.5
million km, approximately half the size of modern India. These
layered basalts are over a mile deep in places. The eroded sediment
from this rock is responsible for fertile soils.
Slide 27
Deccan Traps The Deccan Traps are an example of an LIP (Large
Igneous Province) where basalts have flooded over continental land
masses. There are several throughout the world (including the
Siberian traps and the Columbia Flood Basalts of the western USA)
These events are thought to release large amounts of CO2 and
atmospheric pollutants which could drastically change climate.
Slide 28
Evidence of the K-T extinction event The Cretaceous-Tertiary
extinction event, or the K-T event, is the name given to the
die-off of the dinosaurs and other species that took place some
65.5 mya. For many years, paleontologists believed this event was
caused by climate and geological changes that interrupted the
dinosaurs food supply. However, in the 1980s, father-and- son
scientists Luis (1911-88) and Walter Alvarez (1940-) discovered in
a distinct layer of iridiuman element found in abundance only in
spacethat corresponds to the precise time the dinosaurs died.
Walter and Luis Alvarez standing at the Gubbio Clay layer, the K-T
boundary rich in Ir and microtektites.
Slide 29
Chicxulub Crater This suggests that a comet, asteroid or meteor
impact event may have caused the extinction of the dinosaurs. In
the late 1980s, petroleum geologists working for PEMEX located an
arc shaped gravitational anomaly in the Gulf of Mexico. What they
had found was the massive Chicxulub Crater at the tip of Mexicos
Yucatn Peninsula, which dates to the K-T boundary.
Slide 30
Chicxulub Crater The crater is not visible at the Earths
surface as it is buried in 65 million years of new marine
sediments. Seismic and gravitational anomaly images taken in the
1990s give a clear picture of the location of the crater.
Additionally, it turns out that limestone sinkholes called cenotes
perfectly line the edge of the crater. Artists rendering of the
crater after it was formed
Slide 31
Alternate Theories Besides dinosaurs, many other species of
mammals, amphibians and plants died out at the same time. Over the
years, paleontologists have proposed several theories for this
extensive die-off. One early theory was that small mammals ate
dinosaur eggs, thereby reducing the dinosaur population until it
became unsustainable. Another theory was that dinosaurs bodies
became too big to be operated by their small brains. Some
scientists believed a great plague decimated the dinosaur
population and then spread to the animals that feasted on their
carcasses. Starvation was another possibility: Large dinosaurs
required vast amounts of food and could have stripped bare all the
vegetation in their habitat. But many of these theories are easily
dismissed. If dinosaurs brains were too small to be adaptive, they
would not have flourished for 160 million years. Also, plants do
not have brains nor do they suffer from the same diseases as
animals, so their simultaneous extinction makes these theories less
plausible.
Slide 32
K-T Extinction Videos
http://www.history.com/topics/why-did-the-dinosaurs-die-out History
Channel http://www.youtube.com/watch?v=ubBebEywNmE (KT Asteroid
& Dinosaurs Extinction) (7:05)
http://www.youtube.com/watch?v=ubBebEywNmE
http://www.youtube.com/watch?v=_COcHHvte-0 (2:25) (meteorite
strike) http://www.youtube.com/watch?v=_COcHHvte-0
http://www.youtube.com/watch?v=Dcp0JhwNgmE (Chicxulub Tsunami
(4:05)) http://www.youtube.com/watch?v=Dcp0JhwNgmE
http://www.youtube.com/watch?v=4WwJL25xVG8 (K-T extinction event -
44:44) http://www.youtube.com/watch?v=4WwJL25xVG8
http://www.youtube.com/watch?v=uTvFzm3jRCU (The Siberian Traps and
the Volcanic Mass Extinction Theory (Full Documentary) - Permian
extinction) http://www.youtube.com/watch?v=uTvFzm3jRCU