EARTH AND SPACE SCIENCE

Chapter 9 A View of Earth’s Past9.3 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/spaceweather/FTPRoot/Tellus/homerun/Update3-18/CoelophysisReference?M=A

• Thrinaxodon - http://cas.bellarmine.edu/tietjen/Evolution/triassic_dinosaurs.htm

• Ichthyosaurs - http://www.amnh.org/exhibitions/dinosaurs/gallery/extinction.php?image=6&p=volcanoes&a=foram

• Dinosaur Pelvis Comparison - http://www.txtwriter.com/backgrounders/Dinosaurs/dinoBG3.html

References• Stegosaurus -

http://www.sciotojvs.k12.oh.us/Teachers/Ryan%20Holbrook/NY%20Photo%20CD/NY%20Photos/4.%20The%20American%20Museum%20Of%20Natural%20History

• Pterosaur - http://planetdinosaur.com/non_dinosaurs/rulers_of_the_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/dinosaurs/questions/QnsAug00.shtml

• Cretaceous Impact Site - http://www.physics.uc.edu/~hanson/ASTRO/LECTURENOTES/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.html

• Purgatorius - http://www.paleocene-mammals.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.rhinos-irf.org/education/rhinofactsfiles/rhinofacts/extinctrhinos/woolly

• Mammoth - http://dsc.discovery.com/news/briefs/20051024/mammoth_din_zoom1.html

References• Cave Painting - http://www.artchive.com/artchive

/C/cave/cave_painting_horse.jpg.html• Egyptian Wheat Farmer -

http://www.wsu.edu:8001/vwsu/gened/learn-modules/top_agrev/5-Technology/technology3.html

• Grinnell Glacier Photos - http://www.southbaymobilization.org/newsroom/earth/articles/01.0901.GlacierNatlPark_NoGlaciersIn30Years.htm

• Sea Level Rise - http://pubs.usgs.gov/prof/p1634a/jk_11.htm