Logical Reasoning

PT109 · S4 · Q22 Dinosaur expert: Some paleontologists

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Dinosaur expert: Some paleontologists have claimed that birds are descendants of a group of dinosaurs called dromeosaurs.

Conclusion

The paleo's claim is false. (i.e. Birds are not descendants of dromeosaurs)

Evidence

The earliest bird fossils that have been discovered date back tens of millions of years before the oldest known dromeosaur fossils.

Evaluate

The author is saying, how could species B be a descendant of species D, if we think that B existed millions of years before D did?

Welp --- he's got us there. If birds existed before dromeosaurs, then it's impossible for birds to have descended from dromeosaurs.

How did these "some paleontologists" miss this obvious problem that renders their claim impossible? What could they be thinking that could still allow them to be right and our author to be wrong?

They must be thinking that dromeosaurs existed before birds, so if we point out that , their only retort would be,

Goal

The only possible objection to this argument is to say,

Thus, the argument needs to assume - dromeosaurs did not exist prior to birds - there are not older dromeosaur fossils that got destroyed or have so far not been found by us

22.

The expert's argument depends on assuming which one of the following?

Having similar characteristics is not
Too Strong: not a sign
This author doesn't need to assume that similar characteristics is never a sign that animals are evolutionarily related. If we negate this, does it weaken her argument to hear, "Similar characteristics is a sign that animals are evolutionarily related"? No, this author is fine believing that birds and dromeosaurs are evolutionarily related. Maybe she believes that dromeosaurs are descendants of birds. Maybe she thinks that birds and dromeosaurs are both related to other dinosaurs, and thus have some evolutionary relatives.
11% picked this
Dromeosaurs and birds could have
Not Necessary
The author might believe this, might not. There's no reason why she needs to believe they have a common ancestor. If we negated this, "Dromeosaurs and birds could not have common ancestors", it certainly wouldn't weaken her argument. It actually would strengthen, since it would help this author argue that birds are not descendants of dromeosaurs (if birds were a descendant of the evolutionary branch that included dromeosaurs, then they would definitely have some common ancestors with dromeosaurs).
3% picked this
Knowledge of dromeosaur fossils and
Too Strong: complete
This would definitely be a strengthener, but it's stronger than what the author needs to be true. She just needs it to be true for birds to predate dromeosaurs. We don't necessarily need complete knowledge of dromeo and bird fossils in order to establish that. There could be really insubstantial mysteries about the fossil records of dromeosaurs or birds (like, "We're still not sure which geographic populations of dromeosaurs had this extra long tail bone"). Those lingering mysteries could keep scientists knowledge from being 100% complete, but that wouldn't pose any problem to the author's argument. We know that T-Rex existed earlier than homo sapiens existed, even though our knowledge of T-rex fossils and homo sapiens fossils is still incomplete.
37% picked this
Correct
Known fossils indicate the relative
Why this is right
The author's case rests on the idea that birds came before dromeosaurs, which is what it looks like from the fossils we've discovered thus far. This answer is saying, "The time sequence we can glean from the fossils we've so far discovered is an accurate time sequence". If we have bird fossils that are 10 million years older than dromeosaur fossils, then the relative date of origin of birds was 10 million years earlier than that of dromeosaurs. Negating this answer gives us a big weakener: Yo, author --- even though we have older bird fossils than dromeo fossils, that doesn't mean that birds came before dromeosaurs. After all, known fossils do not indicate the relative dates of origins of those two species.
Skill tested: Necessary Assumption · how this choice captures the argument's function is the move to repeat next time.
49% picked this
Dromeosaurs are dissimilar to birds
Out of Scope
Out of Scope: dissimilar in many ways The author never talked about any dissimilarities. She isn't arguing that birds didn't descend from dromeosaurs because they have many significant dissimilarities. She's arguing that birds didn't descend from dromeosaurs because birds existed 10 million years before dromeosaurs did.
1% picked this

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