Don't waist your time trying to prepare for Jotunheim to tame one of these on Fjordur! There are plenty of Yutys in the north-west snow region of the map!!! You don't need to go to Jotunheim to tame a Yutyrannus!!
So there I was, flying along on my Argent, looking for Daeodons on the family server, and I spy a nearly max-level Yuty with his pack o' Carnos. Naturally - since I've never actually tamed a Yuty before - I messaged my dad to come help, since he was online. So I waited, and watched this pack of nasties chase a low-level Daeodon into the river. Didn't think much of it other than, "Stay out the way of that roar." They all kind of stopped in the frozen bits of the river, so I hopped off the bird and sniped out the Carnos from a safe distance. Dad arrived - "Is that Yuty stuck in the ice?" Turns out it was, and it glitched down into the water when we knocked it out. So we're both going, "Well crap, now it's going to drown." And then it didn't. Yuty tamed up, glitched back up through the ice, and I slapped him into a pod before any other weirdness had a chance to happen.
First day it was released, started a new character made a stone house boat and headed north. Was docked, taming a direwolf. Suddenly it drops from a cliff with 3 carnos. They surrounded my boat and wiped me in three minutes. If you see the buff, gtfo.