In beta 2 (at default settings, tested on the prison and temple maps) catapultasaurus don't spawn as part of the natural reinforcement progression. You can get them via the extra spawn purchase though. (the three as advertised in the purchase, not normal + purchase)
Note: The announcer voice does signal their arrival though, they just don't actually show up.
Come think of it, I haven't seen Angels or Giants spawn either, but I can't confirm that right now.
