So I just now got one unconious, but I did it in the forest/big trees ( heavly populated with them ) and I went on top of a hill in the forest and used a crossbow with tranquilzer arrows, I would really suggest you use it, and just put some meat in it and some narcoberrys and you should be good to go. If it's a high level it will be really difficult.
You will need: icthy with saddle, A nearby leed, a pteranodon with saddle, a carno that you want to tame and (preferably nearby, so your prime meat doesn't rot) 20-25 tranq arrows and a bow. Step 1: After locating a nearby carno hop on your icthy. Step 2: keep scraping meat off your leed, until you get prime fish meat. Step 3: Get your tranq arrows and bow, and fly until you find your carno, and then land on a high rock. Step 4: Get the carno's attention, and get it stuck between two trees. Step 5: hit it with tranq arrows until it's unconsious. Step 6: Give the carno the prime fish meat, and wait. Step 7: Think of a name for your carno while its taming. Suggestions: Toro, Hot Dog, Lil arms and name it according to its colour. ( Moss, Sea foam, Blaze etc.) Step 8: Once its tamed, make sure no dangerous creatures are nearby.(rex, spino, allo pack, etc) Step 9: Hop on your pteranodon, and if the rock is too high request it. Fly back to your base. Step 10: request your carno and name it. Step 11: Congrats! You tamed a carno!
I was running away from pterarons cause I stole a egg I could have killed them but didn't so I ran and I got on top of one of those big rocks and saw a carno stuck in the rocks shot a few traqu arrows and got it tame.