Mesozoic Era
(Age of the Dinosaurs)
225,000,000 years ago to 65,000,000 years ago
Warm Climate
Three Periods
Triassic
Jurassic
Cretaceous
Mesozoic Era
Triassic Period (225-180 MYA)
Pangaea (supercontinent) formed
Mesozoic Era
Triassic Period (225-180 MYA)
First Dinosaurs
(small in size)
Pisanosaurus
Length:3 feet
Height:1 foot
Weight:15 pounds
Eoraptor:
Length:3 feet
Height: 1 foot
Weight:20
pounds
Mesozoic Era
Triassic Period (225-180 MYA)
Conifers and Cycad Forests Dominate (Gymnosperms)
Mesozoic Era
Jurassic Period (180-135 MYA)
Pangaea starts to separate
Mesozoic Era
Jurassic Period (180-135 MYA)
1st mammals (small rodents).
Mesozoic Era
Jurassic Period (180-135 MYA)
1st birds (Archaeopteryx).
• Jaws and bone structure
like dinosaurs
• Bones are hollow, like birds
• Had feathers
Mesozoic Era
Jurassic Period (180-135 MYA)
Reptiles in the sea - Icthyosaurs – 8 m;
Plesiosaurs – 15 m.
Mesozoic Era
Jurassic Period (180-135 MYA)
Dinosaurs Dominate: Allosaurus,
Diplodocus, Brachiosaurus, Stegasaurus.
Mesozoic Era
Cretaceous Period (135-65 MYA)
Continents in modern positions
Mesozoic Era
Cretaceous Period (135-65 MYA)
Flower plants
(angiosperms) evolve
& dominate
Mesozoic Era
Cretaceous Period (135-65 MYA)
Dinosaurs still dominate: T. rex (carnivore);
Triceratops (horned); Trachadon (duckbilled)
Mesozoic Era
Cretaceous Period (135-65 MYA)
Mass Extinction: 50% of all plant and animal
groups die out
Alvarez’s Meteor Impact Theory- 10 km wide
meteorite hits Earth
Mesozoic Era
Cretaceous Period (135-65 MYA)

Evidence of Impact: Iridium



An element that is very rare in Earth rocks and
very common in meteorites
The layer of rocks above the last dinosaur bones
contain ~ 160x normal levels of iridium
Called the K/T Boundary
How could a meteorite impact
cause a mass extinction?
The impact caused shock waves, tidal
waves, and sent a tremendous amount
of dust into the atmosphere
 As the dust re-entered the Earth’s
atmosphere, it would have instantly
heated the atmosphere causing
tremendous forest fires
 Dust from impact blocked out the sun and
caused major climate change and plants
to die
 Plants, animals, etc. went extinct due to
the climate changes and competition
between organisms

Cenozoic Era
(Age of the Mammals)
65,000,000 years ago to Present Day
Two Periods
Tertiary
Quaternary
Cenozoic Era
Tertiary Period
(65 MYA to 1.8 MYA)

Warm and humid climate

Mammals dominate: increasing in size

Earliest prehistoric humans (approx. 4 MYA).

Flowering plants (angiosperms) dominate

Grasses develop, grazing animals become even
larger
Animals of the Tertiary
Organisms that have been found in
the La Brea tar pits of Los Angeles
Megatherium, a giant ground
sloth (20 ft long).
Animals of the Tertiary
Indricotherium, measured up to 13 ft
at the shoulder.
Diatryma, a giant predatory bird.
The Great
Ice Age
Cenozoic Era
Quaternary Period (1.8 MYA to Present)

The “Great Ice Age”, ice sheets covered 30% of all
land

Land & ice bridges connected many continents
allowing animal migration

North American elephants (mastodons, mammoths),
giant sloths & armadillos, and saber-toothed cats go
extinct.

Modern humans evolve, maybe causing the above
extinctions from over hunting.
A Sixth Mass Extinction?
• Are we the cause of a sixth mass extinction that
is currently taking place?
– Round Table Discussion