For decades, evolutionary biologists maintained that early paravians developed powered flight via a ground-up mechanism, utilizing feathered forelimbs to propel themselves upward while pursuing prey. Proponents of this view point to muscle insertion scars on fossilized humeri that indicate strong downward flapping capability. However, recent aerodynamic models of ancestral wing geometry demonstrate that the lift generated by these forelimbs would have been insufficient to overcome gravitational drag without an initial elevation advantage. Because fossilized claw curvature in early paravian specimens closely matches that of modern trunk-climbing birds rather than ground-dwelling runners, the forelimbs were almost certainly utilized primarily to climb trees prior to launching into a glide. Therefore, the contention that flapping motion originated strictly from ground-level cursorial behavior is untenable.
In the argument given, the two boldfaced portions play which of the following roles?
- The first is an opposing hypothesis that the argument as a whole seeks to refute; the second is an intermediate conclusion advanced to support the main conclusion of the argument.Answer
- BThe first is a premise offered to support the author's primary position; the second is the main conclusion of the argument.
- CThe first is an opposing hypothesis that the argument as a whole seeks to refute; the second is the main conclusion that the argument aims to establish.
- DThe first is factual evidence supporting the traditional view; the second is a counterexample used to weaken the author's primary claim.
- EThe first is introductory background information that the author accepts as true; the second is a premise supporting an alternative hypothesis rejected by the author.