Bottle-nose dolphins have an absolute brain mass of 1500-1700 grams, slightly greater than that of humans (1300-1400 grams). Chimpanzees have a brain mass of 420g, rhesus monkeys have an absolute brain mass of 90-97g, while an adult rat’s brain mass is about 2g.

Animals with larger brains are not necessarily smarter than animals with smaller brains. A larger brain is necessary to control larger muscles in larger animals; it is also necessary to process more sensory information from the skin in larger animals.