This boss really isn’t that hard. All you need for yourself is mastercraft or ascendant assault rifle (journeyman will do, but Isn’t as good). Then, to deal with his minions,get 4-5 high level troodons, because they will absolutely WRECK the minions. As tanks, Rexes are, of course, nessecary. And to keep yourself out of trouble, get a fast but durable mount, like an allo or a really high level raptor. Hope this helps!
Before entering the arena take your creatures out of their cryopods (if you use them) because you can't use cryopods in the fight. I found this out the hard way and almost lost all of my boss fighting Dino's. Fortunately if you need to escape the fight once it's started you can leave the game and rejoin and it will place you and your tames at the obelisk (doesn't give summon items back).
If you do forcetame this bad boy after summoning him be careful cause he will literally go apeshit of something attacks to the point even after it's done he never quits I had one absolutely pound everything after a piranha attacked him
Take one velonasaur, buff mainly stamina and melee, some health too and run up to let ledge and stay there in turret mode shooting him. Their too stupid to come up and get you although occasionally a monke will run up at you but he can be taken care of.
Take a male and female gigantopithecus mackerel them breed them do the same again mackerel the babies breed them repeat about 8 times then take the final end product put it in a good hat and go kill this boss!
If you really want to go overboard bring in max dino cap (20 is Max) with at least 17 Rex's and 3 yutyranus. This will obviously increase your chances of killing it, try to level your Rex's in health way more than melee considering you have the yutyranus buff already assisting you or you can go full melee for a glass cannon run. Be aware that this may have a huge risk to it though if you don't have more than MINUMUM 10K health ON HATCH you may or may not die depending on your saddles and or melee damage. Don't forget the rock throw can kill you off of your mount so spread yourselves out if you aren't going to dismount. Otherwise whistle attack target and only mount the yutyranus for the empowerment of the Rex's. The rest of you bring compound bows, snipers, fab pistols, rocket launchers etc. You will also need some focal chilli to increase your chances of survival. Good luck :)