Final answer:
The assumption that allows the conclusion to logically follow is that no chordates are members of Pteropsida. This is because chordates, such as humans, are animals, not vascular plants which Pteropsida represents.
Step-by-step explanation:
In the context provided, the conclusion likely pertains to the relationship between chordates and humans. It is important to clarify that humans are indeed chordates because they have a notochord during some stage of development, which eventually becomes part of the vertebral column. Humans, as part of the family Hominidae, also share the five basic chordate characteristics with other subphyla of chordates. Considering the information and the options provided, the correct assumption necessary for the conclusion to logically follow would be that No chordates are members of Pteropsida, as option 5 states. This is because Pteropsida represents a group of tracheophytes (vascular plants), and based on the information available, chordates are animals and therefore cannot be vascular plants.