Dolphin Killer whales have the second largest brain mass of any animal on earth, next to the sperm whale. The brain to body mass ratio in some is second only to humans. Self-awareness is seen, by some, to be a sign of highly developed, abstract thinking. Self-awareness, though not well-defined scientifically, is believed to be the precursor to more advanced processes like meta-cognitive reasoning (thinking about thinking) that are typical of humans. Research in this field has suggested that cetaceans, among others, possess self-awareness. The most widely used test for self-awareness in animals is the mirror test in which a mirror
Whale shark Whale shark The whale shark ("Rhincodon typus") is a slow-moving, filter-feeding carpet shark and the largest known extant fish species. The largest confirmed individual had a length of and a weight of about . The whale shark holds many records for size in the animal kingdom, most notably being by far the largest living nonmammalian vertebrate. It is the sole member of the genus Rhincodon and the only extant member of the family Rhincodontidae which belongs to the subclass Elasmobranchii in the class Chondrichthyes. Before 1984 it was classified as "Rhiniodon" into Rhinodontidae. The whale shark is found in open