First of all there is old Rooter. Then Littlefoot mentions it in LBT 2 when he tries to comfort Ducky who thinks that the egg with her brother or sister broke. In LBT 6 Littlefoot's grandfather mentions it to Cera's dad (storms being a part of the circle of life rather than being badluck caused by Doc). These three are what comes to my mind spontaneously. I can't think of a fourth one right now, but I'll try to remember.
Just one question, am I correct when I believe it was mentioned in LBT 10, or is that a wrong?