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What do the dinosaurs, the dodo bird and the Tasmanian tiger all have in common? They're all extinct. Countless species have come and gone in the history of our planet, some leaving more of a mark than others. Sometimes the cause of a species' extinction is unknown. To understand and explain these deaths, scientists often work with numerous hypotheses and constantly hunt for more data to unravel the mysteries.
From the fearsome megalodon to the awkward elephant bird, here are some of history's most puzzling extinctions.
Rocky Mountain LocustSlide 2 of 15
Rocky Mountain Locust
When thinking about extinctions, dinosaurs, dodos and other large creatures typically come to mind. But insects can also disappear — and in a relatively short amount of time, too. Between 1873 and 1877, huge swarms of the Rocky Mountain locust (Melanoplus spretus) reportedly caused hundreds of millions of dollars in damage as they ravaged crops throughout the Midwestern United States. Less than 30 years later they were extinct.
So what happened? Many theories point to large-scale environmental changes, such as the disappearance of the buffalo and their locust-breeding wallow habitats. But evidence suggests that innumerable locust eggs may have succumbed to plowing and irrigation used by the very farmers the insects terrorized. Some scientists think that the lack of genetic variation may have added to the locusts' troubles.Slide 3 of 15
MegalodonSlide 4 of 15
Between 28 million and 1.5 million years ago, megalodon ruled Earth's oceans. This terrifyingly large shark, which dined on giant whales with its 7-inch-long (18 cm) teeth, reached a maximum length of over 60 feet and weighed as much as 100 tons. For comparison, great white sharks — megalodon's closest living relative — rarely reach the 20-foot (6 m) mark.
So what could cause a monster at the top of the food chain to sputter out of existence? Theories abound. One idea posits that megalodon couldn't handle the oceanic cooling and sea level drops that came with the ice ages of the late Pliocene and early Pleistocene epochs. On the other hand, another explanation ties the shark's demise to the disappearance of the giant whales it fed on.Slide 5 of 15
Woolly MammothSlide 6 of 15
For 250,000 years, the woolly mammoth (Mammuthus primigenius) enjoyed an expansive range that covered parts of North America, Europe and Asia. A small population survived on Wrangel Island in the Arctic Ocean until 3700 years ago, while the rest of the hairy giants disappeared from their Siberian habitat some 10,000 years ago.
A long-standing theory proposes that early humans hunted the woolly mammoth to extinction. On the other hand, some scientists believe a global shift toward freezing temperatures did the beasts in. But perhaps no single culprit should be blamed. A study detailed online June 12, 2012, in the journal Nature Communications claims that a combination of factorscontributed to the mammoth's downfall.Slide 7 of 15
Broad-Faced PotorooSlide 8 of 15