1. 17-3 Evolution of Multicellular Life
Photo credit: ©D.W. Miller
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Precambrian Time
Precambrian Time
Few fossils exist from Precambrian time because the animals were all________________________.
Life existed only in the___________.
Paleozoic Era
Rich fossil evidence shows that early in the Paleozoic Era, there was a diversity of________life.
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Paleozoic Era
The Paleozoic Era is divided into the following periods:
Cambrian
Ordovician
Silurian
Devonian
Carboniferous
Permian
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Paleozoic Era
Cambrian Period 
The diversification of life at this time is called the “____________________________.”
For the first time, many organisms had_______parts.
The first known representatives of most animal phyla evolved. These included:
_________________(jellyfish, worms, sponges)
___________(small two-shelled animals)
____________(arthropods)
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Paleozoic Era
Ordovician and Silurian Periods
The ancestors of modern octopi and squid appeared.
Some arthropods became the first land animals.
The first vertebrates appeared: _____________which had sucker-like mouths.
The first land plants evolved from aquatic ancestors.
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Paleozoic Era
Devonian Period 
Some plants,__________, adapted to drier areas and invaded more habitats.
Insects, which are_____________, appeared on land.
The Devonian is often called the Age of___________ because many groups of fishes were present in the oceans.
Most fishes had jaws, bony skeletons, and scales.
_____________appeared in the late Devonian.
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Paleozoic Era
During the Devonian, vertebrates began to invade the land.
Fish developed the ability to crawl on leglike fins.
Some of these early four-legged vertebrates evolved into the first____________________.
An amphibian is an animal that lives part of its life in land and part of its life in water.
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8. Carboniferous and Permian Periods
Paleozoic Era
Carboniferous and Permian Periods 
Reptiles evolved from certain________________.
Reptiles have scaly skin and lay eggs with tough, leathery shells.
Winged insects evolved into many forms including dragonflies and______________________.
Giant ferns and other plants formed vast swampy forests.
Remains of ancient plants formed thick deposits of sediment that changed into________over millions of years.
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Paleozoic Era
At the end of the Permian Period, there was a mass extinction in which many living things became extinct at the same time.
The mass extinction at the end of the Paleozoic affected both plants and animals on land and in the seas. As much as_________of the complex life in the oceans disappeared.
Trilobites and many amphibians became extinct, but this mass extinction did not affect many fishes or _______________.
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Mesozoic Era
Mesozoic Era
During the Mesozoic Era, _______________ became dominant. The Mesozoic is also marked by the appearance of ______________________.
The Mesozoic Era is often called the Age of_______.
Triassic Period 
Organisms that survived the Permian mass extinction became the main life forms early in the Triassic.
These organisms included fishes, insects, reptiles, and cone-bearing plants.
___________first appeared during the late Triassic.
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Mesozoic Era
Jurassic Period 
Dinosaurs became the dominant animals on land.
One of the first birds,________________, appeared.
Many paleontologists think that birds are close relatives of dinosaurs.
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Mesozoic Era
Cretaceous Period  
Dominant animals during this period included: reptiles, birds, turtles, crocodiles, fishes, and marine invertebrates.
____________became extinct during the Cretaceous.
New forms of plant life included leafy trees, shrubs, and small flowering plants.
The Cretaceous Period ended with a mass extinction.
More than half of all plant and animal groups were wiped out, including all of the dinosaurs.
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Cenozoic Era
Cenozoic Era
During the Cenozoic, mammals evolved adaptations that allowed them to live in various environments— on land, in water, and even in the air.
The Cenozoic often is called the Age of_________.
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Cenozoic Era
Tertiary Period  
The climate was generally ____________________.
Marine mammals such as whales and dolphins evolved.
On land, flowering plants and insects flourished.
Grasses evolved, providing food for grazing mammals.
Some mammals became very large, as did some birds.
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Cenozoic Era
Quaternary Period   
Earth’s climate cooled, causing a series of_________.
About 20,000 years ago, Earth’s climate began to warm and sea levels began to rise.
In the oceans, algae, coral, mollusks, fishes, and mammals thrived.
Insects, birds, and land mammals were common.
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Cenozoic Era
The fossil record suggests that the early ancestors of our species appeared about______million years ago.
The first fossils of Homo sapiens may have appeared as early as_______________years ago in Africa.
According to one hypothesis, members of our species migrated from Africa and ultimately colonized the world.
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