OG详解-OG9 文法 Q27

Choice C is the best answer. The sentence effectively emphasizes the fossil’s significance, explaining that the fossil is rare and illustrates an early stage in the evolution of pinnipeds from their land-dwelling ancestors. 
Choice A is incorrect. The sentence describes the fossil Rybczynski found; it doesn’t emphasize the fossil’s significance. Choice B is incorrect. The sentence mentions that a fossil resembling both pinnipeds and their ancestors was found; it doesn’t emphasize the fossil’s significance. Choice D is incorrect. The sentence notes a term used to describe the fossil Rybczynski found; it doesn’t emphasize the fossil’s significance.