Elephant

The elephant boasts the largest brain of any land mammal, as well as an impressive encephalization quotient. This is the size of the brain relative to what we'd expect for an animal's body size, and the elephant's EQ is nearly as high as a chimpanzee's. And despite the distant relation, convergent evolution has made it remarkably similar to the human brain, with as many neurons and synapses and a highly developed hippocampus and cerebral cortex. It is the hippocampus, strongly associated with emotion, that aids recollection by encoding important experiences into long-term memories. The ability to distinguish this importance makes elephant memory a complex and adaptable faculty beyond rote memorization. It's what allows elephants who survived a drought in their youth to recognize its warning signs in adulthood, which is why clans with older matriarchs have higher survival rates. Unfortunately, it's also what makes elephants one of the few non-human animals to suffer from post-traumatic stress disorder. The cerebral cortex, on the other hand, enables problem solving, which elephants display in many creative ways. They also tackle problems cooperatively, sometimes even outwitting the researchers and manipulating their partners. And they've grasped basic arithmetic, keeping track of the relative amounts of fruit in two baskets after multiple changes.