CR# 89:Sandactylus and network of blood vessels:

Source: The official Guide for GMAT Review 11th Edition

Network 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, palentologists's 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.

(A) Sandactylus would not have had networks of blood vessels in the sking of its wings if these networks were of no
use of to Sandactylus

(E) Heat generated by Sandactylus in flaping its wings in flight could not have been dispersed by anything other than the blood vessels inits wings.

The diagram for the argument was as follows:

(P): Network of blood vessels disperse heat generated in flight.
(P):Heat generated from flapping.
(P):S: similar network of blood vessels

(C):P: S flew by flapping rather than gliding

I was split between answer choice A and E. I chose E because:
(Denial Test) If you negate E (Heat generated by other means), the conclusion is
invalidated
Also a quick scan through argument and answer choice showed phrases from conclusion tied to premises  an indication of an in-scope
assumption.


(A) also validates the conclusion.

My Q: How did you arrive at the answer choice. In particular, based on your diagram, how did you eliminate E. The explanation in OG is not satisfactory.

Thank you,

Your diagram seems more than sufficient, and you did well to quickly eliminate choices B, C, and D. I agree that answer choices A and E are the two best options, but there is a fundamental flaw with E.

Let's look at your diagram

P): Bats: Network of blood vessels disperse heat generated in flight.
(P):Heat generated from flapping.
(P):S: similar network of blood vessels

(C):P: S flew by flapping rather than gliding

The conclusion of the argument is that S flew by flapping its wings. This is based on its network of blood vessels, a network similar to one that disperses heat in bats. The argument, however, never states that this is THE ONLY WAY that bats disperse heat; it is simply given as one way. Thus, answer choice E is not a necessary assumption. If we negate (E), it reads Heat generated by Sandactylus in flaping its wings in flight could have been dispersed by things other than the blood vessels in its wings. This does not necessarily invalidate our conclusion. However, if we negate (A), it reads Sandactylus would have had networks of blood vessels in the skin of its wings if these networks were of no
use of to Sandactylus . If the vessels were "of no use" to Sandactylus, this directly undermines the evidence on which the entire conclusion is based!

Hope that helps!