My suggestion on this is always try to tame a high lvl anky,cuz' a low level can easily be killed by Rex or a allo pack,they are slow and can't run away,so always try to tame a high lvl one.I tamed a lvl145 anky which was lvl 217 when it was finally tamed,and believe me i got jumped by allo pack ,a Rex(lvl 90) and raptors in a single metal run,my anky smoked all of them ,no didn't even lose 15% of my health,so yeah only tame high lvls.