If you can not trap it, the best thing to do is ure the others from it to rid of the pack bonus and then find a ledge to shoot it from. make sure to have a quick mount near by like a raptor or terror bird because they like to run and since you can fire a crossbow while mounted you can easily keep pace and drop it.
Think about this: The taming in ark is crazy. The last thing the Dino would remember would be you impaling it in the face with toxic arrows before it gets knocked unconscious. And then somehow it eats while knocked out which makes no sense and then wakes up and loves you till it dies.
Yesterday(Oct 21 2020) I tamed to of these beauties! One was lvl 209 and a female wen I tamed it and the other was a male lvl 80! I also bread them,I used a pheromone the baby is fine tho, the tip here is how I tamed them. Ur gonna need a tapejara and tranqs.OK,
1.go to the red woods on ur tapejara
3.land on a tree with ur tapejara
4.WACK TRANQ DARTS ON ALLO HEAD!
5.wen its out, check the area
8.........that's all..........hop u like ur allo......
My name is Ashham and I hop u like it goodbye and..........
if u are going for an allosaures tame the easiest thing you can do is lead one into a taming pen and then kill the others outside that way they do not have the alpha pack boost affect and you can easily and safely knock it out