Dolphins have been declared the world’s second most intelligent creatures after humans, with scientists suggesting they are so bright that they should be treated as “non-human persons.”

“Many dolphin brains are larger than our own and second in mass only to the human brain when corrected for body size,” said Lori Marino, a zoologist at Emory University. “The neuroanatomy suggests psychological continuity between humans and dolphins and has profound implications for the ethics of human-dolphin interactions.”

Researchers have found that brain size varies hugely from around 7oz for smaller cetacean species such as the Ganges River dolphin to more than 19lb for sperm whales, whose brains are the largest on the planet. Human brains, by contrast, range from 2lb-4lb, while a chimp’s brain is about 12oz.