The turtle has the smallest brain, then the opossum, followed by the racoon. Thus the transition from reptile to primitive mammal to advanced mammal indicates an increase in brain size of these groups of animals. Now go back towards the beginning of the displays, and look at the seal skull. Seals use their teeth to spear fish and hold onto them. The teeth of the seal are all very similar as are the teeth of the alligator.
Reptiles have undifferentiated teeth whereas mammals have differentiated teeth.
However, the seal is one example of a reversion to relatively undifferentiated teeth in mammals. Look closely at the jaws of the sheep and alligator. All reptiles have more than one bone in their jaws. The joint in reptile is at the very back of the skull. In the mammal it is moved forward more on the skull.