They were updated in July 2011 with "three complete life stages".
A Creatures 2 conversion is available.
The adult stage of the tiger grendels gives an error since the game runs out of memory for the sprites. To make the adult stage of the Tiger Grendels work, you will need the Bigger Sprite Allocation fix.
The Compatible Tiger Grendels were inspired by this breed, including new art based on them, but meant to correct for several issues with the original.