The trailblazing adventurers roaming the Laramidia of RotPL have it a lot rougher than the cowboys that capture Gwangi, though. This is a lost continent, not just a hidden valley. Huge herds of herbivores eat and trample crops, fearless predators, practically immune to gunfire, have no fear of humans.
Some OSR stats for Gwangi:
Gwangi - Move 180'(60'); HD 15; #AT: 1 bite; DM 4d6; AC: 1(descending)/18(ascending); SA: sever limb, on a natural 20, the target has a random limb bitten off.