These guys only attack you if you do so first. If you want to fight one, watch out for it's tongue attack: It has a very big range and tranqs you. You will definitely have to use ranged weaponry and keep your distance or shoot it from where it can't get to.
If you want to deal with these guys, and tame them, make sure it's a good level, you can just use raw meat it works fine for tame the level doesn't matter too much early game, anyways make sure you have at least 2-3 bolas ready to hold it in place, I just tamed a level 55 and it took 7 tranq arrows with my crossbow. Now run up to it as close as you can (watch out for leaches in the swamp too,) and throw a bola to hold it. Once in place, fire arrows into it only every 4 seconds for better tame, once it's down look at its level and put half of its level as narcotics into it, that's all it'll need. It doesn't need too much meat, and it's sattle isn't too bad to make (considering you're gonna be LV 40 while taming this so you can ride it right away) also if you have any leaches on you, make a campfire as quick as possible and jump in it, the leaches will burn off! Hope this helped!
Me and my tribe mate tried to knock out one of these but it broke the bola and tranqed both of us, we surprisingly survived because it lost aggro on us and hopped away. Be careful though, these guys can seriously deal out some real torpor.