Firstly, welcome aboard! It's great to see new members, let alone ones whom actively participate in the forums ^_^
Now, to answer your question:
The praetorians were only in the video games, and as such are not considered canon.
I have my own theories, but they are a bit extensive to explain on this thread, so I will instead give you the link to my xenomorph biology thread:
http://www.alienvspredator2.com/comments/11675.html
It contains all of my theories and explanations about xenomorphs, so it should be pretty helpful. Hope you like it ^_^
And thus I clothe my naked villainy
With old odd ends stolen forth from holy writ
And seem a saint when most I play the devil.