Dinosaur expert: Some paleontologists

Answer choices

1. A

   Too Strong: not a sign11% picked this

   Having similar characteristics is not a sign that types of animals

   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%
2. B

   Not Necessary3% picked this

   Dromeosaurs and birds could have common

   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%
3. C

   Too Strong: complete37% picked this

   Knowledge of dromeosaur fossils and the earliest bird fossils

   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%
4. D

   Correct48% picked this

   Known fossils indicate the relative dates of origin of birds

   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.

   48%
5. E

   Out of Scope1% picked this

   Dromeosaurs are dissimilar to birds in many

   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%