Answer: B. The fossils of mammoth bones were similar but different to modern elephants.
Explanation: The evidence that Cuvier used to conclude that the world used to be full of species that are no longer around today was B. The fossils of mammoth bones were similar but different to modern elephants. By examining the bones of mammoths, Cuvier was able to identify differences between them and modern elephants, leading him to conclude that mammoths were a distinct species that once existed but no longer does. This was part of Cuvier's larger argument for the concept of extinction, which was controversial at the time.