Um, that's a toughy...platformer with RPG elements? It's a side scroller, and you do quite a bit of jumping when you gain legs. Each time period has a story with characters in it, but most of the levels are just your standard "left to right" area with different prehistoric critters in them. At the end of each time period you'll face a boss creature, once you beat it you go on to the next chapter. You get stronger by biting things to death and consuming the tasty meat they leave behind. This meat gives you points that you can use to evolve different body parts. Like this:
Biting things to death can feel a bit repetitive, but the variety of things you can bite to death is impresive. The sprites have a lot of life to them, and it's just fun designing your creature and seeing how the body parts affect your abilities.
EDIT: Oh god, now I really want to play this game again! Arrgh!