Sea-Rex!
Oddworld at the time in which it's set at the moment has enough creatures at is, even with all the experiments and extinctions. I imagine pre-historic Oddworld to be completely FULL of creatures of all shapes and sizes. There's no real way to describe them unless you drew a picture... which makes me wish my scanner worked. It is good to think that Oddworld once had no forms of 'intelligent' life.
Or, maybe Pre-historic Oddworld was... Earth! *gasp*
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