If you're on PvE like myself, you're going to need to first bola the alpha and then gate it in with 4 wooden Dino gateways and their coinciding doors. Just make a square around them. Then, wait for the other hyena's to be a far enough distance from the alpha/cage and then cage them in as well. I did each hyena individually because they spook otherwise.
A word worthy of note, Hyaenodon's WILL attack in large packs. Stick to a group of three, including the alpha.
Also worthy to note that alpha's occasionally enter some sort of rage mode and can quickly break free from bola's.
After you've got your hyena's caged, fly out of render distance to lose aggro and then fly back in and proceed with the tame.
You still need your ghillie suit and to be crouched.
These are only one time uses so make sure to demolish for resources after you're done!
Good luck out there!
Normally you can't tame the pack leader, so just get a pteranodon or argy, pick it up and drop it in a large area (like a separate section of your base). When you take it away from the rest of the pack, it removes its 'pack leader' title, allowing you to tame the highest level hyena of that pack.
Despite it's appearance, the real life hyaenodon was nowhere near related to actual hyenas, but it actually belongs to a group of prehistoric mammals, all extinct, that are believed to be most closely related to pangolins, which aren't related to anteaters or armadillos, for your information.
Build a 1x1 box with door frames and throw a hatch ceiling and 4 more regular walls up and throw it in, it's butt will hang down and you can crouch and pet it under it without spooking it. You CAN tame without alpha present but if it becomes spooked you have to leave your chunk and let it reset.