Even the earliest known species of land animals, known from fossils da

Question

Competition Mode Question

Even the earliest known species of land animals, known from fossils dating from the late Silurian period, 400 million years ago, show highly evolved adaptations to life on land. Since neither aquatic nor amphibious animals exhibit these adaptations, early species of land animals must have evolved very rapidly after leaving an aquatic environment.

Which one of the following is an assumption on which the argument depends?

(A) Known fossils of early land animals include fossils of animals that lived relatively soon after the first emergence of land animals.

(B) Fossils from the late Silurian period represent only a small number of the animal species that were alive at that time.

(C) No plants were established on land before the late Silurian period.

(D) No present-day species of aquatic animal is descended from a species of animal that once lived on land.

(E) All animals alive in the late Silurian period lived either exclusively on land or exclusively in the water.

exc4libur · Answer

argument
= earliest land animals show highly evolved adapts to land
= since neither aquatic or amphi show these adapts
= land animals must have evolved rapidly after leaving water

assumption
(B) irev
(C) irev
(D) argument is regarding those that evolved from aquatic, not inverse
(E) irev

ans (A) if known fossils didn't include those of animals that lived soon after the first emergence, the conclusion falls.

debjit1990 · Answer

Ans: A

(A) Known fossils of early land animals include fossils of animals that lived relatively soon after the first emergence of land animals.

we could only say the land animals evolved very rapidly if we knew that the fossils dated from fairly soon right after the land animals emerged. Otherwise, if the fossils dated from a much later period, then the land animals may have remained the same for a very long time, before evolving to show the adaptations in these fossils

TheGraceful · Answer

Excellent question and definitely hard one.

Hi  Bunuel ,
can you please provide official explanation...?

BinodBhai · Answer

The provided answer (A) is indeed the correct assumption. Here's why:

Let's break down the argument again:

* **Premise:** The *earliest known* land animal fossils (400 million years ago) already show highly evolved adaptations for land life.
* **Premise:** Aquatic/amphibious animals don't show these adaptations.
* **Conclusion:** Therefore, land animals must have evolved *very rapidly* after leaving the water.

**The Gap and the Assumption:**

The argument *jumps* from "earliest known" to implying "earliest *to exist*." For the conclusion of rapid evolution to hold, we must assume that the fossils we've found represent a stage relatively close to the actual initial emergence of land animals.

If assumption (A) is *false*, meaning the known fossils are *not* from relatively soon after the first emergence of land animals (i.e., there were much earlier, perhaps less-evolved, land animals that we haven't found yet), then the conclusion of rapid evolution falls apart. If land animals existed much earlier but just haven't been fossilized/discovered, then the 400-million-year-old highly evolved fossils don't necessarily imply rapid evolution; there would have been a longer period for evolution to occur.

Therefore, the argument depends on the assumption that the fossil record we have (showing highly evolved adaptations) isn't missing a significant, earlier, less-evolved phase of land animal evolution. Option (A) captures this perfectly.

licrolicro · Answer

The argument states that the earliest known land animal fossils from the late Silurian period already show highly evolved adaptations to land, and since neither aquatic nor amphibious animals have these adaptations, the evolution must have happened very rapidly after leaving water.

We need to identify the assumption—the unstated premise that is necessary for the argument to hold.
Breaking it down:

The argument claims that land animals evolved their adaptations very quickly after transitioning from water.

The evidence is that the earliest known fossils already show these adaptations, and no aquatic/amphibious animals have them.

For this reasoning to work, the earliest known fossils must be from animals that lived shortly after the transition to land. If there were earlier land animals (not yet discovered) that took a long time to evolve these adaptations, the argument falls apart.

Evaluating the options:

(A) Known fossils of early land animals include fossils of animals that lived relatively soon after the first emergence of land animals.
 → This matches our analysis. If the fossils are from shortly after the transition, then the rapid evolution claim holds. If not, the argument weakens. This is the assumption.

(B) Fossils from the late Silurian period represent only a small number of the animal species that were alive at that time.
 → Irrelevant. The argument isn’t about how many species existed, but about the speed of evolution.

(C) No plants were established on land before the late Silurian period.
 → Irrelevant. The argument is about animal adaptations, not plants.

(D) No present-day species of aquatic animal is descended from a species of animal that once lived on land.
 → Irrelevant. The argument is about early land animals, not modern ones or reverse transitions.

(E) All animals alive in the late Silurian period lived either exclusively on land or exclusively in the water.
 → This would rule out amphibious animals, but the argument already acknowledges that amphibious animals don’t have these adaptations. This isn’t a necessary assumption.

Correct Answer:

(A) Known fossils of early land animals include fossils of animals that lived relatively soon after the first emergence of land animals.

This is the assumption because if the fossils were from much later (after a long, slow evolution), the argument’s conclusion about rapid evolution would fail. The argument depends on the idea that we’re seeing fossils from very close to the transition point.

Even the earliest known species of land animals, known from fossils da

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Even the earliest known species of land animals, known from fossils da

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