I recently had the opportunity as part of this class to take a look at the skulls of different mammals, and it was an interesting look into how these skulls some in a great variety of shapes, but that a similar shape may still apply to many mammals. In this case, I decided to split up the types of mammal skulls into three. I could have made more or fewer divisions, but at the time I decided to split them into these three categories: land quadrupeds, marine mammals, and primates.
As I decided to classify it, land quadrupeds are obviously characterized by the tendency to live on land and to walk on four legs. Additionally, they typically on fields or mountains, or tended by humans. These type of mammals include goats, giraffes, wolves, and cats. As for their skulls, the length of the skull is usually about twice that of the height, and the snout is fairly elongated.
Next, I designated marine mammals to be those mammals like dolphins and whales that, as would be expected, live in the ocean. These skulls are even more elongated, as it is not uncommon to see these type of skull be three or more times as long as they are tall. Additionally, the snout is very long and thin and actually can make up more than half of the skulls extreme length.
Finally, primates include humans, in addition to all the human's close relatives like chimpanzees or apes that generally live in rain forests. Primate skulls are far more rounded than the skulls of the marine mammals or land quadrupeds, as they have a length that is about equal to their height.
All in all, this is how I, as a layperson, decided to classify these animals based on their skulls. I know that this was mainly only based on two criterion: length of the skull in relation to the height, and general habitat of each mammal, but considering the context, I felt like I did an alright enough job.