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GIANT SLOTH

When it went extinct: About 11,000 years ago

How: Hunting by humans

Where it lived: The Americas

Size: As long as 20 feet, up to 9,000 pounds

Diet: Ate plants but also scavenged for meat

Random fact: Had claws as long as 20 inches

Why we might be able to bring it back: DNA samples found in fossil dung in Utah

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CUBAN RED MACAW

When it went extinct: Last sightings in the late 1800s

How: Hunting, nesting trees felled to capture young birds for the pet trade

Where it lived: Cuba

Size: Approximately 20 inches long

Diet: Seeds

Random fact: Even though its meat was said to smell and taste bad, people still dined on red macaw.

Why we might be able to bring it back:Specimens in Cuba contain DNA samples.

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NEW ZEALAND GIANT MOA

When it went extinct: Circa A.D. 1400

How: Hunting

Where it lived: New Zealand

Size: As tall as 8 feet, up to 500 pounds

Diet: Probably fed on plants

Random fact: The moa did not have wings.

Why we might be able to bring it back: DNA found in fossil eggs and feathers in New Zealand

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TASMANIAN TIGER (ALSO KNOWN AS A THYLACINE)

When it went extinct: Last recorded sighting in the 1930s

How: Hunting, habitat loss

Where it lived: Tasmania, Australia, and New Guinea

Size: Over 4 feet long, around 75 pounds

Diet: Preyed on kangaroos, small rodents, birds

Random fact: People who saw the animal reported that it could open its jaw nearly 180 degrees wide.

Why we might be able to bring it back:Cloning is a possibility with preserved DNA from a specimen at the Australian Museum.

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SABER-TOOTHED CAT

When it went extinct: Circa at 10,000 B.C.

How: Probably hunting by humans

Where it lived: North and South America

Size: Around 6 feet long, up to 900 pounds

Diet: Preyed on such mammals as bison, deer, horses

Random fact: It's the official state fossil of California.

Why we might be able to bring it back: DNA is preserved in bones at the La Brea Tar Pits in Los Angeles.

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PASSENGER PIGEON

When it went extinct: 1914

How: Hunting, habitat destruction

Where it lived: North America

Size: About 15 to 17 inches long

Diet: Seeds, worms, insects

Random fact: The last known bird, named Martha, died at the Cincinnati Zoo.

Why we might be able to bring it back: There are some 1,500 preserved passenger pigeon specimens with extractable DNA.

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DODO

When it went extinct: Late 1600s

How: Mainly because on the island where it lived, newly introduced species like dogs ate chicks and eggs.

Where it lived: Mauritius

Size: About 3 feet tall

Diet: Fruit, seeds

Random fact: Lived only on the small island of Mauritius, east of Madagascar in the Indian Ocean

Why we might be able to bring it back: Two skeletons have been found containing DNA samples.

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WOOLLY MAMMOTH

When it went extinct: About 3,700 years ago

How: Hunting, habitat loss due to climate change

Where it lived: Parts of northern Asia, Europe, and North America

Size: 9 to 11 feet tall, about 1,400 pounds

Diet: Grass and other plants

Random fact: Remains of a 37,000-year-old woolly mammoth calf were found in Russia.