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EARTH AND
SPACE SCIENCE
Chapter 9 A View of Earth’s Past
9.3 The Mesozoic and Cenozoic
Eras
9.3 The Mesozoic and Cenozoic
Eras Objectives
• List the periods of the Mesozoic and
Cenozoic Eras.
• Identify two major geologic and biological
developments during the Mesozoic Era.
• Identify two major geologic and biological
developments during the Cenozoic Era.
Introduction
• The greatest extinction event known to have occurred
marks the boundary between the Paleozoic and
Mesozoic Eras.
• The Permian-Triassic mass extinction claimed 90% of
marine species and 70% of terrestrial species.
• The surviving life forms had a number of niches
available to exploit as a result of the loss of so many
species.
• Adaptive radiation of surviving species into newly
vacated niches resulted in an abundance of new life
forms appearing on Earth at this time.
• Some of these life forms flourished while others went
extinct.
The Mesozoic Era
• The Mesozoic Era of time spans from about 251
million years ago to 65 million years ago.
• As Pangaea broke into smaller continents, plates
drifted and collided.
• The Sierra Nevada (California) and Andes (South
America) began to form.
• In general, the climate for much of the Mesozoic was
warm and humid with many shallow seas and
marshes.
• The Mesozoic is known as the Age of the Reptiles
due to the diversification and abundance of many
forms of reptiles – including the dinosaurs!
The Mesozoic Era
• The Triassic was the first period of the Mesozoic.
• Dinosaurs first appear in the fossil record in
Triassic rocks.
• Dinosaurs ranged in size from smaller than a
chicken to 30 m long weighing over 15 tons,
though most Triassic dinosaurs were 4 m to 5 m
long and moved quickly.
• Lush forests with cone bearing trees and cycads
dominated much of the landscape, though there
were arid regions more like today’s deserts.
The Mesozoic Era
• The Triassic oceans contained ichthyosaurs
(marine reptiles that had adapted a fish-like
shape) and invertebrate cephalopods called
ammonites.
• Ammonites diversified so rapidly, were
widespread, and readily identified so they are
often used as Mesozoic index fossils.
• Small, rodent-like forest dwellers also
appeared during the Triassic.
The Mesozoic Era
• Two major groups of dinosaurs had evolved
to become the dominant form of life by the
Jurassic Period.
• The hip-bone structure is used to distinguish
the two major groups of dinosaurs.
• The saurischians (lizard-hipped dinosaurs)
include herbivores, and carnivores.
• The sauropods, like Apatosaurus – 50 tons
and 25 m long, were among the largest of the
dinosaurs.
The Mesozoic Era
• The ornithischians (bird-hipped
dinosaurs) included only herbivores.
• Stegosaurus (9 m long, 3 m tall) was
one of the better known ornithischians.
• Pterosaurus, a flying reptile, was
common in the Jurassic skies.
• Archaeopterix, one of the earliest
undisputed birds, dates back to the
Jurassic Period.
The Mesozoic Era
• The most popular of all dinosaur species,
Tyranosaurus rex, lived during the late Cretaceous
Period.
• T. rex stood up to 6 m tall and was about 15 m long.
• Ankylosaurs, ceratopsians, and hadrosaurs were also
common during this final period of the dinosaurs’
reign.
• The earliest angiosperms (flowing plants) appeared
during the Cretaceous.
• Magnolias and willows were among the most
common of these early flowering plants.
The Mesozoic Era
• The Cretaceous Period (last of the Mesozoic Era)
ended with a mass extinction that brought about the
end of the dinosaurs and many large marine reptiles.
• Some scientists have credited the movement of
continents (plate tectonics) and volcanic activity for
this mass extinction.
• A more popular explanation among many scientists is
the impact hypothesis which credits the mass
extinction to a meteorite impact.
• The impact raised dust which blocked much of the
sun’s light for months or even years.
The Mesozoic Era
• The lack of sunlight reaching the Earth
caused obvious problems for most plant life
and cooled the Earth’s climate considerably.
• The rapid climate change and destruction of
much vegetation precipitated a domino effect
among the animals on Earth.
• An iridium layer is found in the very last layer
of Cretaceous rocks to be deposited at may
sites globally.
• Iridium is a common element in meteorites,
but very rare on Earth.
The Cenozoic Era
• The Cenozoic Era is the unit of geologic time that
began about 65 million years ago and continues
through modern day.
• The continents have migrated to their current position
and mountain chains such as the Alps in Europe and
the Himalayas have been uplifted.
• Major climate changes have occurred throughout the
Cenozoic.
• At times, continental ice sheets have covered nearly
33% of the Earth’s land mass.
• Mammals have reached an amazing degree of
diversity during this time, also known as the Age of
Mammals.
The Cenozoic Era
• The Tertiary Period
of the Cenozoic Era
spans time from 65
million years ago up
to the time before
the last series of ice
ages (about 2.6
million years ago).
• The Quaternary
Period includes the
last 2.6 million
years of Earth’s
history – ice ages
and the modern
Holocene Epoch.
The Cenozoic Era
• During the
Paleocene, the
earliest epoch of
the Cenozoic,
many new
mammals evolved
such as small
rodents and early
primates.
• These Paleocene
primates were
much like today’s
prosimian
primates.
Purgatorius
The Cenozoic Era
• Many mammal
forms diversified in
the Eocene epoch
including whales,
bats, and the
earliest known
horses.
• Alabama’s state
fossil is the Eocene
whale Basilosaurus
cetoides (left).
The Cenozoic Era
• Worldwide, the climate became significantly
cooler and dryer in the Oligocene Epoch.
• In this cooler climate (average temperature
had already dropped an average of 4°C by
the end of the preceding Eocene Epoch),
grasses, hardwoods, and conifers flourished.
• Many early species of mammals became
extinct as larger mammals became more
predominant such as deer, horses, pigs,
camels, cats, and dogs.
• Marine invertebrates continued to diversify.
The Cenozoic Era
• During the Miocene Epoch, the Antarctic
icecap began to form as circumpolar currents
began to form around the continent.
• Tectonic forces and falling sea levels caused
the Mediterranean Sea to dry up and fill
several times.
• The largest of land mammals, the
Paraceratherium transouralicum (4.5 m tall,
15 tons), lived during this time.
• The earliest of the saber-toothed cats date
back to the Miocene Epoch.
Paraceratherium transouralicum
The Cenozoic Era
• Predators such as bear, dog, and cat families evolved
into modern form.
• Large herbivores, such as the giant ground sloth
flourished during this time.
• Giant ice sheets began to spread near the end of the
Pliocene Epoch – a drop in sea level occurred as a
consequence of water being trapped in ice.
• The Bering land bridge was exposed between
Eurasia and North America and the isthmus of
Panama formed between Central America and South
America.
• The presence of the bridges allowed for migration of
species to previously inaccessible land.
The Cenozoic Era
• The Pleistocene Epoch began about 1.8
million years ago and lasted until about
11,500 years ago.
• Many ice ages occurred during the
Pleistocene Epoch.
• Some animals adapted to cooler weather with
thick fur coats while others migrated.
• Fossils of the earliest modern humans are
found in Pleistocene deposits.
• Some early humans in the late Pleistocene
left cave paintings.
The Cenozoic Era
• The Holocene Epoch (a.k.a. Recent Epoch)
began about 11,500 years ago around the
end of the last glacial episode.
• During that time, ice sheets have melted and
sea level has risen about 140 m.
• Homo sapiens developed agricultural
methods and metal tools.
• Compared to the history of life on Earth,
human history is rather brief.
References
• Triassic Scene (Coelophysis) http://earth.rice.edu/Space_Update/updating/spacew
eather/FTPRoot/Tellus/homerun/Update318/CoelophysisReference?M=A
• Thrinaxodon http://cas.bellarmine.edu/tietjen/Evolution/triassic_din
osaurs.htm
• Ichthyosaurs http://www.amnh.org/exhibitions/dinosaurs/gallery/ext
inction.php?image=6&p=volcanoes&a=foram
• Dinosaur Pelvis Comparison http://www.txtwriter.com/backgrounders/Dinosaurs/di
noBG3.html
References
• Stegosaurus http://www.sciotojvs.k12.oh.us/Teachers/Ryan%20Ho
lbrook/NY%20Photo%20CD/NY%20Photos/4.%20Th
e%20American%20Museum%20Of%20Natural%20H
istory
• Pterosaur http://planetdinosaur.com/non_dinosaurs/rulers_of_th
e_sky/pterosaurs.htm
• Archaeopteryx http://people.eku.edu/ritchisong/554notes1.html
• Tyrannosaurus rex (both images) http://www.michaelcovel.com/trex.html
References
• Triceratops http://www.sdgs.usd.edu/fossil.html
• Cladogram of Land Plants http://www.enchantedlearning.com/subjects/di
nosaurs/questions/QnsAug00.shtml
• Cretaceous Impact Site http://www.physics.uc.edu/~hanson/ASTRO/L
ECTURENOTES/F01/Lec17/Page5.html
• Impact Illustration http://www.wa.gov.au/tiac/forum/2001/hocking
/famous/chixpic3.htm
References
• Ice Age Move Image http://www.impawards.com/2002/ice_age.htm
l
• Purgatorius - http://www.paleocenemammals.de/primates.htm
• Basilosaurus cetoides http://www.mheine.com/pbasilo.html
• Horse Evolution http://pharyngula.org/index/weblog/comments
/iconic_horse_evolution
References
• Eocene Bat http://www.uvm.edu/~jdecher/Lecture11.html
• Indricothere http://www.cgnetworks.com/story_custom.php
?story_id=395&page=
• Wooly Rhino - http://www.rhinosirf.org/education/rhinofactsfiles/rhinofacts
/extinctrhinos/woolly
• Mammoth http://dsc.discovery.com/news/briefs/2005
1024/mammoth_din_zoom1.html
References
• Cave Painting http://www.artchive.com/artchive/C/cave/cave_pai
nting_horse.jpg.html
• Egyptian Wheat Farmer http://www.wsu.edu:8001/vwsu/gened/learnmodules/top_agrev/5Technology/technology3.html
• Grinnell Glacier Photos http://www.southbaymobilization.org/newsroom/e
arth/articles/01.0901.GlacierNatlPark_NoGlaciersI
n30Years.htm
• Sea Level Rise http://pubs.usgs.gov/prof/p1634a/jk_11.htm