Forerunner has 3 toughness.
1 Dino Enters - Triggers Forerunner
First Forerunner Trigger Resolves
2 Dinos Enter - 2 Forerunner Triggers go on the stack (Note - it triggers for every dino) - 1 Damage marked on Forerunner
First of 2 Forerunner Triggers resolve - creates 6 Dinos - 6 Forerunner Triggers go on the stack before the initial second forerunner trigger - 2 damage marked on Forerunner
First of the 6 forerunner Triggers resolve - 3 Damage marked on Forerunner and he dies due to state based actions - 18 Dinos Enter
The remaining 6 secondary Forerunner Triggers still resolve
So yes...that's 9 forerunner triggers because the stack DOES work that way.