How are different animal's brains different?
Different animals need to be able to do different things. If an animal is really good at one thing, then the part of its brain that controls that thing tends to be bigger. For example, dogs have a really good sense of smell. So more of their brain is devoted to sensing and identifying odors. Dolphins have a really good sense of hearing. More of their brain is devoted to listening to and understanding sounds. Birds have very precise vision. So some areas that are involved with vision are bigger in birds. Brains of closely related species look more similar. For example, humans are closely related to gorillas (both are primates). Also, different animals' brains take on different shapes partly depending on the shape of their head! Here are some brains from different animals.
Another thing that is different between different animals' brains is how many wrinkles and folds they have. This happens because the sheet of tissue that forms the outer part of the brain, the cortex, is bigger in some animals. In order to pack all that cortex into the skull, it wrinkles and folds up as it grows! It's similar to how you can crinkle up a piece of paper in order to make it nice and small to fit in the trash can.
What part of the human brain is bigger? Well, many different parts of the human brain are relatively large. Humans are good at many different things. One thing that humans are really good at is thinking, reasoning, and planning. The part of the brain that controls these skills is called the prefrontal lobe. Humans' prefrontal lobes are bigger than other animals'.