PrepTest 102, Section 2, Question 12
It has long been thought that lizards evolved(64 more words not shown)
An assumption made in the(6 more words not shown)
- Aunknown anthracosaur fossils(5 more words not shown)
- Bunknown lizard fossils(5 more words not shown)
- Cknown lizard fossils(5 more words not shown)
- Dknown anthracosaur fossils(5 more words not shown)
- Eknown lizard fossils(4 more words not shown)
Reading the argument
Not finding an older fossil doesn't prove the animal wasn't there.
The dates do create an apparent problem for the proposed ancestry. Our known lizard fossil is 340 million years old, while no anthracosaur fossils have been found in rocks older than 300 million years. If anthracosaurs really arrived later than lizards, lizards couldn't have evolved from them.
But those are dates of discoveries in the fossil record, not a complete record of when each creature existed. What if anthracosaurs lived 400 million years ago and we simply haven't found their fossils yet? Or what if some early individuals never left fossils? The missing discoveries don't establish that the creatures themselves were missing.
That is the gap: the author treats the oldest known evidence as a limit on the animal's actual history.
What we’re looking for
The question asks what the argument assumes there are no examples of. I'd look for older, undiscovered anthracosaur fossils that could put those creatures before the 340-million-year-old lizard. Discovering such evidence would remove the timeline problem used to reject the ancestry, though it wouldn't by itself prove the ancestry true.
Working the answers
- ACorrect
The argument assumes there are no unknown anthracosaur fossils older than 340 million years. If those fossils existed, anthracosaurs could predate the lizard fossil despite the younger age of everything found so far. That would defeat the argument's basis for declaring the proposed evolution impossible. Remember the stem's “there are no”: the assumption excludes the older evidence that could undermine the conclusion.
- B
Older unknown lizard fossils would move lizards still farther back. They wouldn't solve the author's problem of supposed ancestors arriving too late. The argument needn't assume every earlier lizard fossil has already been found in order to claim the known lizard is too old for the proposed ancestry.
- C
A known lizard fossil predating some anthracosaur fossils fits the dates already given. Indeed, the 340-million-year-old lizard predates the known anthracosaur evidence described. The author isn't assuming this situation never occurs; it helps create the apparent difficulty.
- D
Some anthracosaur fossils could predate some relatively recent lizard fossils without changing which group existed first. A 300-million-year-old anthracosaur could be older than a 100-million-year-old lizard while still being younger than the lizard fossil that creates the problem. The argument doesn't need to rule out that overlap.
- E
An uncertainly dated lizard fossil needn't disturb the inference based on the estimated 340-million-year-old specimen. The argument doesn't require every known lizard fossil to have a settled age. The missing assurance concerns how far back anthracosaurs existed, not universal certainty about every lizard fossil.
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