Logical Reasoning

PT1 · S4 · Q3 In 1860 Bavarian quarry workers

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In 1860 Bavarian quarry workers discovered the impression of a feather in a limestone slab dating to the Mesozoic era.

Conclusion (therefore)

The feather found in the Mesozoic limestone must have belonged to the earliest bird to date.

Evidence

We didn't think birds evolved until post-Mesozoic.

The imprint in this limesone is a fully aerodynamic, 3-inch long feather.

Evaluate

The author is interpreting this Curious imprint as belonging to a bird.

CURIOUS FACT: what explains this imprint of a 3-inch fully aerodynamic feather in a piece of Mesozoic limestone?

AUTHOR'S EXPLANATION: Birds existed in Mesozoic times, and this feather is from one of them.

We know, with the Explain Curious Fact style of argument, that we should consider: 1. alternate explanations of the curious fact 2. how plausible the author's explanation is

With Flaw / Weaken / Nec Assump / Eval, the alternate explanation style correct answer is at least twice as likely as the plausibility style answer.

What else could explain this 3-inch feather imprint? - maybe it was a cute li'l baby pterosaur's feather? - maybe a bird came along much later but somehow got its feather imprinted on this 10 million year old limestone from the Mesozoic era.

Goal

The correct answer will rule out an alternate explanation for the imprint or it will supply some idea that would need to be true for the author's storyline to be plausible.

3.

The argument assumes which one of the following?

  1. The creature to which the

    Out of Scope

    The argument doesn't need the bird to descend from pterosaurs. Whether the bird's ancestry traces through pterosaurs, some other lineage, or independent evolution, the argument's assumption that this feather belonged to a bird is unaffected. (This is really an outside knowledge trap, if you know that birds most likely evolved from dinosaurs.)

    5% picked this

  2. Birds with such feathers were

    Out of Scope

    This would almost certainly be true, because it's very unlikely that evolution would jump straight from no feathers to fully aerodynamic 3-inch long feathers. But it's not necessary. If evolution DID jump straight from no feathers to these fully developed 3-inch feathers, it doesn't mess up any of the author's argument. If anything, by saying, "This must have been the earliest bird", the author is acting like there isn't a less-developed version of bird that came before this.

    2% picked this

  3. Correct

    In the Mesozoic era, no

    Why this is right

    This is Defending the argument by Ruling Out an Alternate Explanation. If other creatures besides birds also had feathers like these, then we wouldn't get to look at this feather imprint and conclude, "Oh, this was from a Mesozoic bird!" It could be from one of the other feathered creatures. Negating this answer weakens the argument by creating the possibility of an Alternate Explanation for the evidence.

    Skill tested: Necessary Assumption · how this choice captures the argument's function is the move to repeat next time.

    89% picked this

  4. The feather belonged to a

    Bad Assumption

    The author concludes that this was the earliest bird, or at least the earliest we've found so far. This answer says "she doesn't think the feather belonged to a pterosaur or to a bird". She definitely thinks this feather belonged to a bird! She doesn't say, "Thus, we've discovered a transition species between pterosaur and birds", she says "Thus, this was a bird".

    4% picked this

  5. The earliest bird flew in

    Out of Scope

    How well or awkwardly the bird flew is irrelevant. We're just trying to diagnose whether this feather came from a bird, not how gracefully the supposed-bird could fly.

    0% picked this

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