When taming a high level megalosaurus, you need to put down right when night starts. It sounds counterproductive because it's stronger, but it allows for maximum starve time since you will need to put it down again the following night. If you don't do it this way, you may end up needing to put it down a third time, which could very likely be the death of it since it won't regain any health over that time.
Also, tame with a friend because the megalosaurus will pick you up into its jaws which makes it very hard to do solo without dying. Your tribe mate can attack the Dino and cause him to drop you.
I tamed one with tranquilliser arrows and a slingshot. It was even level 130. If you want to tame one I suggest finding it at night and waiting till day to tranquillise it because if it’s night it will wake up instantly
Tame the mega during the day! It is extremly slower during the day due to wanting a rest. It is a very strong dino, it has been tested to be even stronger than the allo! Be careful if you tame it at night ;) caw
Don't tame one in the transition of day-night. I was feeding him kibble, he was about to be tamed and darkness fell... He got up, I had to re-tranq him and even though he didn't lose a lot of the taming bar, my kibble disappeared :(