For today, we're doing tiny big things! Does that seem like an oxymoron? It isn't really, because everything that does get big has to start somewhere.
With that said, let's go!
ELEPHANTS
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Bonus video!
RHINOS
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HIPPOS
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BEARS

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Bonus video 2!
Aw, aren't those kind of cute? You know what's coming up, though!
The largest spider (by mass, not size-) spider is the Goliath Birdeater Spider. Even though the Giant Huntsman spider is larger than it is, it can still grow up to a hefty 12 inches from toe to toe!

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Here's a picture of an adult on someone's hand. And as for the baby version:

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This little guy's a lot more awkward and spindly, isn't it? Seems like most youngsters of any species are like that.