This list ranks the 15 smartest animal species from least to most intelligent, with sheep ranked 15th, pigeons 14th, rats 13th, octopuses 12th, and squirrels 11th. Pigs are 10th, cats 9th, dogs 8th, parrots 7th, and crows 6th. Elephants are 5th, monkeys 4th, whales 3rd, dolphins 2nd, and apes are considered the most intelligent animal.