The largest mammalian brain belongs to the sperm whale, one of the biggest cetaceans in the sea. The sperm whale's head comprises 25 to 35 percent of its entire body length. The mature adult sperm whale's brain weighs an average of 18 pounds, and can grow to be nearly 500 cubic inches in size. For comparison, the human brain is only about 80 cubic inches. Compared to the exceptional size of the sperm whale, however, the brain itself is not that large: the brain mass is only .02 percent of the total body mass.
The brain of the elephant is the largest contained by any living land-dwelling mammal. The adult male elephant's brain can grow to be a whopping 12 pounds. As with the sperm whale, the brain accounts for relatively little of the elephant's total body mass. The elephant's brain accounts for roughly .1 percent of its mass, and is uniquely located at the back of its head, not at the front.
The famous extinct bird dodo, popularly thought to be stupid, was actually quite smart, new research shows. Its brain size compared to its body size was on par with pigeons, who are considered to be moderately intelligent, said researchers who analyzed a preserved dodo skull. Paleontologist Mark Norell of the American Museum of Natural History in New York explained how the dodo got its reputation: “It had a catchy name, had a ridiculous appearance, was flightless, and because of its lack of fear toward humans, probably due to its isolated habitat, made easy prey”.
Manta Rays have huge brains — the biggest of any fish — with especially developed areas for learning, problem solving and communicating. The giant rays are playful, curious, all signs of self-awareness. A manta’s brain can be ten times larger than a whale shark’s. Not only is the brain physically big, it’s also large relative to the ray’s body. That’s another sign of super smartness, true of elephants, dolphins and people too. Mantas have enlarged brain areas, associated with intelligence, vision and motor coordination. Some brain cells too, are physically more like those in birds and mammals than in other fish.
Mantas also ACT smart. They flaunt their intelligence in behavioral tests that use mirrors to check for self-awareness. Only a few species, including great apes and bottlenose dolphins, can recognize their own reflections, rather than attacking or ignoring the mirror.