In the history of life on Earth, evolutionary forces have pushed some species to become incredibly large. After most dinosaurs died off 66 million years ago, some mammals and marsupials grew bigger and bigger, taking the dinos' place.
What's so great about living large? A size advantage can help you escape predators or attack prey, and crowd out others for resources. During cooler periods, larger animals may find it easier to stay warm. And, interestingly, giants tend to need to eat much less, relative to their size, than pipsqueaks.
In other words:
The past is packed with monsters! Behemoths by the dozen!Let's meet these fossils (and their less colossal modern cousins). The capybara's now the largest rodent on the planetBut Earth once housed a mighty mouse ten times more titanicWith twelve-inch-long incisors — J. monesi wins the prizeIt truly was a rodent of a most unusual size You think this hog is homely? Well you'd better brace yourself!Cause here's a hippo relative they call the pig from hellAs burly as a big bad wolf, with emphasis on bigThe Daeodon had all the strength of thirty little pigs The wombat is Australian. It has a rock-hard rearIn combat with its ancient kin it wouldn't win, I fearBoth wonders from Down Under raised their young inside of pouchesBut only one marsupial is bigger than most couches Behold the crafty crocodile complete with toothy grinNow see a Sarcosuchus smile — five feet from cheek to chinAnd speaking of dentition this big shark's name means big teeth*So its "now extinct" condition should be a huge relief If sloth's a sin then someone hurry up and call a priestCause here's a Megatherium — four tons of sloth, at leastWith jumbo tongue, colossal claws, and tail braced on the groundIt grazed for leaves high in the trees where modern sloths are found The rhino you and I know weighs at least a couple tonsBut if you dare — compare a ParaceratheriumThe largest vegetarian you'd ever care to seeIt was hornless and quite harmless ... unless you were a tree And that's just the beginning. There's more — I could go on!Stupendous Stupendemys! Don't forget Procoptodon!The armoured Doedicorus! Meganeura's footlong wings!The plus-size penguin from Peru they call the Water King! But there's one beast that bests them all; in fact it breaks the scale:Balaenoptera musculus. Its common name? Blue whale!Four hundred thousand pounds — the largest creature known to scienceAnd so today we still can say we share the Earth with giants
Many of the huge animals in this video lived in the Pleistocene, roughly 2.5 million to 11,000 years ago. Their extinction over the past 60,000 years has been linked to early human hunters and to a changing climate. You can see all these species in infographic form on our tumblr.
*Megalodon means "big teeth."
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