I tamed one of this with upper lvl ptera:).

1-Find an Allo group.

2-Kill the Allos, leave the one you want alive (i would recommend to get the stronger). Farm the others, you can get prime.

3- knock it out. Get in a high place, and shoot it tranq arrows, with crossbow. Where I found it, there was like a canon(?), so I atractted it there shooted it in ustedes

4- Feed it prime or mutton, and give it some narcotics or biotoxin. (I used prime bc I play mobile, there's no mutton)

5-Protect until tamed.

Hope it works, I tamed lvl 38 like this:) (on casual.)

Plz up if it helped!

(Sorry for bad spelling, english isn't my first language)