You can remove any creature you don't like by adding this line to your Game.ini file, swapping out the creature for the ID listed on the Spawn Codes Page . Make a new line for each creature

NPCReplacements=(FromClassName="Example_Character_BP_C", ToClassName="")

So to remove ichtynoris and microraptors, for example:
NPCReplacements=(FromClassName="Ichthyornis_Character_BP_Aberrant_EAV_C",ToClassName="")
NPCReplacements=(FromClassName="Microraptor_Character_BP_Aberrant_EAV_C",ToClassName="")