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# Even the earliest known species of land animals, known from

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Even the earliest known species of land animals, known from [#permalink]

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29 Mar 2005, 05:34
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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.

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29 Mar 2005, 09:14
Changed my mind on this. It's (A) for me. If a fossil is found that lived much later, then we can't determine if animal adaptation to land was rapid or not.

(E) is out-of-scope.

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29 Mar 2005, 11:41
seems like "E" to me, author seems to be assuming that the earliest land animals were aquatic before moving on to land i. there were no amphibians at that time.

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29 Mar 2005, 12:09
I believe it is (A).

If an animal did not evolve quickly to adapt to the land conditions then that animal would have died very soon. To conclude that they evolved quickly we have to assume that they lived for reasonable amount of time.
this is what (A) says.

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29 Mar 2005, 12:29
guess I don't understand what "A" is saying what does "animals that lived relatively soon after the first" mean ? I don't see how this statement has anything to do with the stem. Honghu/Anand cud u explain ?

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29 Mar 2005, 12:32
Fact1: The earliest known species of land animals show highly evolved adaptations to life on land.
Fact2: Neither aquatic nor amphibious animals exhibit these adaptations.
Conclusion: Early species of land animals must have evolved very rapidly after leaving an aquatic environment.

(A) Known fossils of early land animals include fossils of animals that lived relatively soon after the first emergence of land animals.
If this is not true then it is likely that there are other land animals that lived earlier than late Silurian period. And those animals may have partial evovled adaptations. In other words it is possible that land animals have evolved slowly, only we haven't discovered the fossils for those first animals.

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29 Mar 2005, 12:37
banerjeea_98 wrote:
guess I don't understand what "A" is saying what does "animals that lived relatively soon after the first" mean ? I don't see how this statement has anything to do with the stem. Honghu/Anand cud u explain ?

I couldn't make sense out of A either that's why i didn't even try to analyze it.

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29 Mar 2005, 13:37
its A,
As only A supports the conclusion that the chage was very rapid in the adaptations.
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i hate when people do'nt post the OA, it leaves in guessing!!!!

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31 Mar 2005, 19:20
Thanks all

OA is A. Sorry for late.

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31 Mar 2005, 20:00
(A) Known fossils of early land animals include fossils of animals that lived relatively soon after the first emergence of land animals.
- This tells us that soon after emergence, the land animals developed the adaptations (i.e. rapidly). If they did not exhibit this, then developement must be slow.

(B) Fossils from the late Silurian period represent only a small number of the animal species that were alive at that time.
- Not important. We just need to know if lands animals developed rapidly after leaving an aquatic environment.

(C) No plants were established on land before the late Silurian period.
- Out of scope

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

(E) All animals alive in the late Silurian period lived either exclusively on land or exclusively in the water.
- If the animals live exlusively in certain environement, then the land creatures couldn't have come from the sea. So this choice weakens the conclusion.

A it is.

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29 Dec 2013, 10:47
Folaa3 wrote:
banerjeea_98 wrote:
guess I don't understand what "A" is saying what does "animals that lived relatively soon after the first" mean ? I don't see how this statement has anything to do with the stem. Honghu/Anand cud u explain ?

I couldn't make sense out of A either that's why i didn't even try to analyze it.
A says that we have fossils of land animal X(say cow) just after land animals emerged on land(say 1600 million years ago).
This initial fossil(of cow of 1600 million years ago) is very important to us because only with this fossil, we can tell whether the land animals whose fossil was found of 400 million years ago really made good progress from timeframe 1600 million years ago to timeframe of 400 million years ago.

If the question is around rate(of change), you must know the timeframe to calculate the change.

(A) Known fossils of early land animals include fossils of animals that lived relatively soon after the first emergence of land animals. A explained as above
(B) Fossils from the late Silurian period represent only a small number of the animal species that were alive at that time.Even if you have less or more of fossils, still they will be able to prove, so no effect on argument
(C) No plants were established on land before the late Silurian period.Plants are out of scope. Argument is about animals, in fact specifically land animals
(D) No present-day species of aquatic animal is descended from a species of animal that once lived on land.Same as D.
(E) All animals alive in the late Silurian period lived either exclusively on land or exclusively in the water.By negating this choice, even if we say that animals would have lived on land as well as water, we cant comment anything on rate of evolution. Moreover, this again moves away from land animals.
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Re:   [#permalink] 29 Dec 2013, 10:47
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