【導(dǎo)讀】mammals.andland-dwellingmammals.cetaceans.birthonland.○Exact. ○Scarce. ○Valuable. ○Initial. ○Hearingstructures. ○Skullshapes. ○B(yǎng)reedinglocations. ○Pakicetus. ○Fish. ○Life. ○ocean. legs.○Explained. ○Visible. ○Identified. ○Located. ○Livedatthesa