Some scientists think that Meganeura were actually too big to be able to survive in the current atmosphere, citing the higher oxygen concentration in the prehistoric world as the only way an insect its size would be able to breathe in enough to support its massive body. By all accounts, this makes Meganeura one of the biggest bullets ever dodged by the human race, because if one of them collided with a bug zapper the resulting inferno would probably burn down your entire backyard.

Why it's a Good Thing They're Dead:

That.

"Giant scorpion" was all this thing needed in its name to be pretty f*****g terrifying. Jaekelopterus rhenaniae, the largest bug on record, managed to up the ante by being an ancient giant scorpion from beneath the waves. It may just be us, but that makes it way worse somehow.

Jaekelopterus lived in freshwater lakes and streams, unleashing all eight-feet of its anthropodic rage on unsuspecting victims. Though referred to as a sea scorpion, it was really more of an oversized lobster, a fact which does nothing to decrease its hideousness. Or its claws, which were the size of a grown man's head.

Why it's a Good Thing They're Dead:

We already depend on fresh water as an alternative to swimming in the ocean, because rivers tend to be relatively free of massive lurking predators. Having six or seven prehistoric death lobsters crawling around in the silt would seriously affect the "wow" factor of that weekend at your uncle's lake house. Also, the amount of food a scavenging beast like Jaekelopterus would need to consume would reduce fishing trips to a level of boredom the human mind can barely comprehend.

We as humans are already pretty envious of birds--they can fly around and s**t on anything they want, something we'd need both a jetpack and precision diarrhea to accomplish.

As if answering the dare to make us feel more inadequate, the world gave us Argentavis magnificens, the largest flying bird in recorded history. These beasts possessed a wingspan between 19- and 26-feet, and a wing area of 75-feet, which you may notice is only slightly smaller than a Lear Jet. In addition to its staggering size and 240-pound weight, the bird is believed to have swallowed prey as large as cattle in one fell swoop.

Why it's a Good Thing They're Dead:

Backyards would not be fenced. They'd be caged. Blue skies wouldn't be a beacon of hope so much as a grim reminder of your own mortality. Say good bye to bicycles, convertibles, outdoor sporting events. When birds the size of a Volkswagen are patrolling the skies, anything that doesn't involve a sky-raptor resistant roof over your head officially falls under the category of "not f*****g worth it." Half of the Gross National Product would need to be devoted to the construction of giant scarecrows, which depending on how gullible they were, would only work on the birds who'd seen Voltron.

Why it's a Good Thing They're Dead:

Like most extinct mammals from the Ice Age, Arctodus competed pretty heavily with human beings for the same natural resources (food and water). We really only came out on top because we figured out how to make weapons first, so if these bears were still hanging around, it's entirely possible we'd still be competing with them, only instead of trout and berries it would be for waterfront property and lucrative employment opportunities.

Also, it could knock your goddamn head off with one blow, and who needs that kind of stress.

Josephoartigasia monesi, the largest rodent ever discovered, was roughly the size of a hippopotamus and every bit as adorable. These beasts were five-feet high, 10-feet long and likely weighed over a ton--large enough to have towed Cinderella to her prom without any of that "bibbidy-bobbidy" bullshit.

Their mouths packed incisors that were over a foot long, and though their diet was most likely vegetarian, teeth that size could easily deliver a bite worse than Christian Slater in a nightclub.

Why it's a Good Thing They're Dead:

Rodents are fairly irritating pests as it is, so imagine the damage one the size of a pygmy elephant could do to the community. The amount of vegetation (and cheese) necessary to sustain a monsei for just one day would probably be more than an entire family of people eat in a week, and considering the rate at which rats reproduce, thinning out the ranks of a whole oversized colony would become part of your daily routine just to keep from starving to death.

Much more impressive was Carcharodon megalodon, the largest fish in history and the star of more made-for-cable movies than Lorenzo Lamas and Casper Van Dien combined. At 70-feet long, this magnificent bastard was more than three times the size of an average great white shark and large enough to swallow an average sedan.

Why it's a Good Thing They're Dead:

We shouldn't really have to explain this. Between great whites, moray eels and 160-foot long Voltron-jellyfish already in the ocean, it's scary enough to go swimming without a beast from the Old Testament sniffing around for your blood.

The largest anaconda on record stretches a considerable 27-feet at its proudest moments.

However, its ancestor Titanoboa cerrejonensis (yes, it is actually called the Titanoboa) grew to lengths anywhere between 40- and 50-feet, weighed in at two and a half thousand pounds, and could probably crush you to death with a harsh glance. Without dispute, it is the most ass-blastingly enormous snake that has ever existed.

The Titanoboa lived about 60 million years ago and actually survived the extinction event that killed all the dinosaurs, effectively curling up its tail and smacking natural selection directly in the testicles, staving off death for several more millennia.

Why it's a Good Thing They're Dead:

Despite the unmitigated supervillain awesomeness of its name, the Titanboa could probably eat the entire student body of an elementary school in an afternoon, which could be seriously damaging to the future of the fast food industry. On the plus side, the careers of Casper Van Dien and Lorenzo Lamas would create enough tax revenue to end world hunger.

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We aren't finished frightening you yet. Check out Nature's 6 Most Diabolical Predators and The 5 Most Horrifying Bugs in the World.

Stop by our Top Picks (Updated 3.8.2010) Seanbaby wrestling the last Meganeura in existence.

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