The highest level Allosaurus will become an Alpha if at least one other is nearby; you do not need 3 to gain the Alpha Bonus.
The best way I find to breed Allo's is to find a pack with 1 150, kill off the other two and tame a 150 Allo. Do this for 2 150 Allosauruses and you can breed a nasty army of these things. You'll be able to take on Rex's like they're dodo's. Wyverns make for east kills, too. Just watch out for Alpha's.
The only thing a good pack of Allo's cannot take on, is a wild Giga.
If you really think about it, these are SOOO underrated. Incredibly high damage and speed. A pack of 10 is easily better than a Giga. 3-4 ballista bolts, (lvl 29 btw) can make a Giga rage, and ballista bolts have a VERY long range, so... you’re dead if you’re riding it. Against a level 30 player. You see 10 Allos coming for you? Run for your ballista? 3-4 Allos dead, still 7 Allos killing you. Even rockets against 10 or so Allos? Crap. You’re still dead. They are so fast and can 20 shot ANY creature in the game if it’s an alpha. Yes, Titantos? Dead in 20 shots. (5% of the creatures health over time.) (Doesn’t work on bosses.) Compared to a Rex, an alpha Allo is arguably equal. Base stats of the Rex are 1100 health and 62 damage. Alpha Allo is 787.5 health and 52.5 damage. They have much faster DPS than Rexes and have better stamina, allowing for more overall damage. Not as much health, but still. To a wild Giga (level 1) with the alpha attack they deal 4000 damage. 4000!!!!!!!!!!
Pretty awesome tames... It's the perfect tame between a raptor and a Rex. When I started off in a new server I could get a level 80 allo before my stone base was even enclosed properly! I slapped a saddle on that bad boy and got another level 85 allo. I now also have 3 low level carno's for the heck of it and I can defend my base without any X plants! They are perfect to kill Rex's brontos or anything not stronger than a Giga! It's pretty easy to tame once knocked out. I just fed it biotoxin every ten minutes on mobile. They're very, very, very fast. I have 145 speed and they are fast enough to not just catch up but even attack me. When trying to tame get them running through the forest. That will thin the crowd and takes away the Pack Leader buff from the high level allo. Lure it in a trap and a free Rex raptor mix is yours! Btw. Just two allo's gives you a pack leader buff on the highest level allo you have, so you know which one is gonna be my ride...