These have some properties that made them great as a first tame:
1. They are EVERYWHERE - you can get yourself a couple of these and no dino will be a match to you, except Theri, that thing will wreck all of you, recommend getting at least 10 to take it out.
2. They are easy to tame - if yours are being slaughtered, they can at least buy you time to run away and you can recruit some new ones right away.
3. They spit blinding poison - I think the poison affect all dino, even the big one, so not only it will weaken your enemy and make it more vulnerable, but in case they are not winning, you still have time to run away.