Networks of blood vessels in bats' wings serve only to disperse heat

StandardizedNerd

Networks of blood vessels in bats' wings serve only to disperse heat generated in flight. This heat is generated only because bats flap their wings. Thus paleontologists' recent discovery that the winged dinosaur Sandactylus had similar networks of blood vessels in the skin of its wings provides evidence for the hypothesis that Sandactylus flew by flapping its wings, not just by gliding.

Argument: Networks of blood vessel -> ONLY to disperse heat -> Heat is ONLY because of flapping of wings
Same networks found in Sandactylus wing, so hypothesis - Sandactylus flew by flapping its wings- is strengthened.

The argument in the passage relies on which of the following assumptions?

A) Sandactylus would not have had networks of blood vessels in the skin of its wings if these networks were of no use to Sandactylus.
After going through all options, I would stick to this option as all other are way off the mark.
This assumption would have been more appealing if somewhere in the argument, it could have mentioned that the purpose of these networks is ONLY to dissipate heat. The argument does stress on ONLY but only in case of the bats. We have to stretch that to Sandactylus too.
Nevertheless, there is no other better option.

B) All creatures that fly by flapping their wings have networks of blood vessels in the skin of their wings.
We are looking for the opposite.
'All creatures that have networks of blood vessels in the skin of their wings fly by flapping their wings' would be a perfect assumption.

C) Winged dinosaurs that flapped their wings in flight would have been able to fly more effectively than winged dinosaurs that could only glide.
Effectiveness - we are not comparing the efficiency of flights.

D) If Sandactylus flew by flapping its wings, then paleontologists would certainly be able to find some evidence that it did so.
The paleontologists are doing a great job. But how is it connected to network of blood vessels pointing towards flapping wings.

E) Heat generated by Sandactylus in flapping its wings in flight could not have been dispersed by anything other than the blood vessels in its wings.
This would surely help incase argument was about proving that Sandactylus had blood vessels in its wings. But here WHAT(Heat generated by Sandactylus in flapping its wings) we are using to prove something else is exactly what we require to prove.

Although A leaves room for a bit of error, there is no better choice than A.