I have seen a razortooth between the redwoods and the white cliffs, but Im not too sure about the other creatures. Where is the mod placed on your mod list, it can effect if the mod works or not also do you have any other mods that add in creatures that might clash? also the razortooth seems to be a modded yutyrannus, so i would suggest checking the snow to see if there are any there.

razortooth doesnt spawn in the snow. rather, the jungle and redwoods.