A dorsal hollow nerve cord, notochord, paired pharyngeal gill slits, and post-anal tail are the four fundamental features shown by all chordates. Crocodiles, dogfish, whales, and penguins all belong to the phylum Chordata.The nervous system in chordates is hollow.Mammals, including aquatic ones like whales, don't lay an egg.Dogfish belong to cartilaginous fishes in which the endoskeleton is made of cartilage.They possess pharyngeal gill slits during the embryonic developmental stage, if not in the adult stage.Thus, the correct answer is option D.