Before the total extinction of dinosaurs, mammals lay suspended. They were primitive things, hardly larger than the eggs of their supreme neighbors, and scavenging for insects and other "small" nutrition. It was not until the Cenozoic that the mammals had a chance to shine. Then, they became much more advanced than their predecessors ever were. A major difference between these types of animals is their solutions to the problem of giving birth. Dinosaurs laid their eggs and left them without protection and they gave no attention to the young once they were born. The young therefore were often in danger. Birds, at least, incubated their eggs in a nest to keep them safe. Different types of mammals had different ways of solving this problem. A type of primitive mammal, the monotreme, laid eggs. [The creature feature of the Paleocene is a Platypus, a monotreme.] A marsupial, on the other hand, gave birth to live young, though they were premature and under-developed. The larger of the marsupials carried them in their pouches until they were ready for life in the outside. The most advanced type of mammal is the placental kind. They were (and are) much more efficient than any other type of mammals before them. Since the females had placentas, their young are born much more developed. This makes them more resistant to predator attack. The development of the two advanced types led to the extinction of most monotremes, who just could not compete. There are only three species living today. Being warm-blooded was another advantage. These animals did not have to wait for the sun to warm them up before they could be active. But they also need more energy, and therefore warm-blooded animals need more food and oxygen. The diaphragm muscle was developed to satisfy this need. Another interesting fact is that mammals can breathe while they eat, because of air can pass through their noses. Mammals' teeth are also much more useful for grinding food. Mesozoic mammals were little more than scavengers and fruit eaters (spurred by the outburst of flowering plants). These feeding habits allowed the mammal digestive systems to evolve. After the extinction of dinosaurs, mammals went from their "ecological obscurity" to an animal "power-house" in the Cenozoic. And that led to us.	Mammal Ungulates (Hooved Ones)
	Pyrotherium
	Placental Mice