This original sentence is correct as written. The word "fossils" is correctly placed as the subject of the opening modifier "hailed as a key discovery in the science of evolution." Also, the plural noun "fossils" agrees with the plural verb "provide."
(A) CORRECT. This choice is correct as it repeats the original sentence.
(B) In this choice, "a large scaly creature" is incorrectly placed as the subject of the opening modifier "hailed as a key discovery in the science of evolution." The fossils of the creature – not the creature itself – were discovered. Moreover, the phrase "a large scaly creature . . . provides fossils that are a possible link" distorts the meaning of the sentence by nonsensically suggesting that the creature "provides" its fossils; in fact the fossils were simply discovered by scientists.
(C) In this choice, "a large scaly creature" is incorrectly placed as the subject of the opening modifier "hailed as a key discovery in the science of evolution." The fossils of the creature – not the creature itself – were discovered.
(D) This choice correctly places the word "fossils" as the subject of the opening modifier "hailed as a key discovery in the science of evolution." However, this choice incorrectly employs the singular verb "provides," which does not agree with the plural noun "fossils."
(E) This choice subtly changes the meaning of the original sentence. The use of the word "and" in the phrase "the fossils resemble . . . and provide" creates two distinct points: first, that the fossils resemble x, and, second, that the fossils provide y. In contrast, in the original phrase "the fossils of a large scaly creature resembling both a fish and a land-animal provide evidence of . . .," the focus is clearly on how the fossils provide evidence. The modifying phrase "resembling both a fish and a land-animal" demonstrates how the fossils provide that evidence – it is not intended as a separate, unrelated point.