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

Let's start by nailing down the conclusion. Is the conclusion that "Sandactylus flew by flapping its wings, not just by gliding."? Not quite... that is the hypothesis. The author's conclusion is that the "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."

So the author is not simply trying to conclude that Sandactylus flew by flapping its wings (or that Sandactylus DEFINITELY flew by flapping its wings). Instead, the author is trying to make the case that the recent discovery provides evidence for the hypothesis stated above.

Now that the distinction between the hypothesis and the conclusion is clear, let's review the author's argument:

• Bats have networks of blood vessels in their wings, and those blood vessels disperse heat generated in flight.
• "This heat is generated only because bats flap their wings." - This implies that if the bats did NOT flap their wings, then they would not generate the heat and thus would not need the blood vessels in their wings to disperse that heat.
• Paleontologists' have recently discovered that Sandactylus had similar networks of blood vessels in their wings.
• According to the author, that discovery provides evidence for the hypothesis (that "Sandactylus flew by flapping its wings, not just by gliding"). Does the hypothesis imply that Sandactylus never used gliding during flight? No. It simply says that gliding was not the ONLY method. So, if the hypothesis is correct, Sandactylus certainly could have used some gliding, but it MUST have used wing-flapping too.

Now that we understand the argument, we need an assumption on which that argument depends:


Bats only need the blood vessel networks because they flap their wings. If we assume that Sandactylus actually used the networks, then we'd have reason to believe that those networks were used only for heat dispersion, not for any other purpose.

But what if the networks were not used at all? Just because an animal has a feature that CAN be used for some purpose, does that necessarily mean that the animal actually uses that feature? If the networks in Sandactylus actually served no purpose, then we would have no reason to suspect that they flapped their wings. Thus, (A) is a required assumption.


It doesn't matter whether all creatures that fly by flapping their wings have networks of blood vessels in the skin of their wings. The author is simply arguing that the discovery "provides evidence for the hypothesis that Sandactylus flew by flapping its wings." For example, not EVERYONE who has a fancy car has a lot of money. However, having a fancy sports car can still be evidence that someone has a lot of money. Eliminate (B).


We don't care about the effectiveness of wing-flapping vs. gliding. We are only concerned with whether networks of blood vessels in the wings are evidence of wing-flapping. (C) is irrelevant and can be eliminated.


What other evidence paleontologists may or may not find is irrelevant. We KNOW that paleontologists have recently discovered "that the winged dinosaur Sandactylus had similar networks of blood vessels in the skin of its wings." According to the author, that discovery alone provides evidence for the hypothesis.

Also, remember that we don't actually care whether Sandactylus flew by flapping its wings. The author is not trying to prove that this is true. The author is simply arguing that the blood vessel networks are evidence that Sandactylus flew by flapping its wings. (D) is not a required assumption and can be eliminated.


Sandactylus may have had several mechanisms for heat dispersion. As long as the networks of blood vessels in their wings comprised one of those mechanisms, the author's argument would hold. Eliminate (E).

(A) is the best answer.