Human goddamn beings.
Every time I hear somebody say things like "Oh humans are rubbish, we don't have any natural weapons and we're all squishy and so easy to kill how have we even survived" I am compelled to sit them down and explain how human beings are the best damn animal in the world. For the purposes of this thread I will assume you said the above phrase, and go get a cup of tea. Do sit down and let me introduce you to Alan, a prehistoric human.
First point, the lack of natural weapons. Sure, claws are cool, a spiked club on the end of your tail would be badass, and everybody somewhere deep down inside wants to be able to spit acid at people they don't like. We've got stubby little blunt instruments on the end of our limbs, and I guess we could headbutt stuff with our unusually large head? That must be what it's for, right? Dear me no. See, we've got a big well-protected head because our giant brain is damn clever. In particular, for tool-using.
For example, there's some food up in a tree. Now for a wolf or something, that'd be the end of it and they'd go on with their day. For a goat I guess they could take the time to climb up and get it, but that'd waste valuable energy and they might get et. Now imagine a creature with long, rigid extrusions on the end of it's arms. It could easily reach up and whack the food out of the tree. Alan can't reach. However, he spies a branch nearby, picks it up, and whacks the food out of the tree, just as well as the imaginary creature with sticks on it's arms.
Lets have another example, a more carnivorous one perhaps.
There's a deer sleeping in a field near a copse of trees. Here, the imaginary creature won't do so well. It'd have to stand far away to get a good swing with it's long spindly extrusions, and if the trees were close together it'd be bloody hard to quietly move among the trees. Alan spies a nearby rock, picks it up, sneaks through the trees with his lack of large appendages and soft feet, and bashes the deer's head in.
Perhaps you can see what I'm getting at. Human hands aren't a weapon, they're a weapons platform. We have, effectively, all the weapons, rather than being restricted to just one or two. We don't have claws, we made swords and various other sharp pointy weapons. We don't have clubs, we...well, made clubs. Metal clubs! Suck on that, ankylosaurus. It took us a while, but we do now have acid sprays and flamethrowers and lasers and all manner of weapons that outclass other animal's so well that we're, ah, sort of endangering them. You don't get to be top of the food chain without any weapons.
Onto the next point, our...squishyness. You're right, we don't have anything cool like armour plating and/or the ability to roll into a ball like the armadillo or I guess the woodlouse. I'm sure you've learned by now and you're expecting the blah blah we made our own armour out of the corpses of animals we killed blah blah we're a platform whatever. You're completely right (and by you I mean me) but that's not what I'm about to say. NB: I am not a doctor or vet, please tell me if I'm wrong because I'd hate to inadvertently spread misinformation.
You know how if a horse breaks a leg it's fucked? We put them down because it's more humane than attempting to set the bone so that it heals properly, because that requires that weight be taken off it. Horses aren't suited to being still, or living on three legs. Meanwhile people break their legs everyday, no problem. Stick it in a splint, don't knock it around for a while, and you'll be fine.
Blood loss. We can lose 30% of our blood and be relatively fine, just need to get some more fluids and rest a while. Most animals can tolerate around 10-15% and need a blood transfusion to survive any more.
Finally, we don't need any more protection. Prehistoric human's strategy was not to go up to a tiger and punch it into submission. Prehistoric human's strategy was to stay the hell away from tigers, or keep them at the other end of a pointy stick if that couldn't be avoided. Then, if worst comes to worst and the tiger gets around your cunning defence system, you hope that my next point comes into play.
Buddies! Humans are a social animal, and hopefully Alan's mates had just gone for a piss behind a bush somewhere nearby. They can then intervene with quite an arsenal at their disposal (assuming they've figured out how to tie things to other things, but even if not) and the all-important element of surprise, and they will hopefully see the tiger off. Alan's in a bad way, he's got quite a gash on his arm and he's feeling a bit woozy. Alan's mates use whatever's at hand to press the wound and staunch the bleeding, and carry him home. Good old Alan's mates.
And with that short tale, hopefully you're satisfied that yes, humans really are the dominant species and it wasn't some weird fluke of luck that the lion was ill the day we were chosen. I'm not going to go into psychological resilience, or how we learn, or human stress reactions and reflexes and a whole host of fascinating phenomena that have set us squarely above every other animal here, because I really don't know enough about them to say. Anyway, thanks for listening.