This sentence involves two opinions: that dinosaurs were warm-blooded and that they were cold-blooded. For the first blank, we need a word describing this difference, something like "contrast." In the second part of the sentence, we see that the opinion that they were cold-blooded does something to evidence in the fossil record (a fossil is a sign of a living being from ancient times, preserved in rock). Since we know that scientists proposed this notion "in order to" do this thing to evidence, we can assume it would be positive, probably along the lines of confirming it.
Looking at the answers, we have three words that refer to the conflict of views: choice (A) "contrast with," choice (C), "a challenge to," and choice (E), "a departure from." We should exclude choice (C), since the SAT would say "as a challenge" rather than "in a challenge"; also, we know that the new view was proposed in order to do something with evidence, not to challenge the old one. Choices (A) and (E) are both suitable, so we need to look at the second words in them. Choice (A), "unearth," means "to find something that was buried in the earth," and although the question does refer to fossils, it doesn't make sense when we're talking about doing something to evidence. Choice (E), "account for," means "provide an explanation for," and it fits in this context.
The correct answer is (E).
This question comes to you from approximately 65 million years B.C.