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.
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.
(B) All creatures that fly by flapping their wings have networks of blood vessels in the skin of their wings.
(C) Winged dinosaurs that flapped their wings in flight would have been able to fly more effectively than winged dinosaurs that could only glide.
(D) If Sandactylus flew by flapping its wings, then paleontologists would certainly be able to find some evidence that it did so.
(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.

The given passage compares presence of similar structures, the blood vessels, in the wings of bats and winged dinosaur Sandactylus to explain the unknown function of wings in the dinosaur species. Bats are flying mammals and use wings to fly. The blood vessels in their wings serve to spread out the heat that is produced by flapping of wings during flying.

The presence of blood vessels in wings of dinosaur Sandactylus suggests that they also used wings for flying. If Sandactylus species did not use the wings for flying, their wings should not have blood vessels as gliding movement does not require it.