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Section 32-1: Introduction to the Mammals
In addition to having hair and the ability to nourish their young with milk, all mammals breathe air and are endotherms that generate their body heat internally.
The first true mammals appeared during the late Triassic Period, about 220 million years ago.
The ability of mammals to regulate their body heat from within is an example of homeostasis.
As mammals evolved to eat foods other than insects, the form and function of their jaws and teeth became adapted to their diets.
The kidneys of mammals help maintain homeostasis by excreting or retaining excess liquid.
Section 32-2: Diversity of Mammals
The three groups of living mammals are the monotremes, the marsupials, and the placentals. Marsupials bear live young that complete their development in a pouch. Monotremes lay eggs. In placental mammals, nutrients, oxygen, carbon dioxide, and wastes are exchanged between embryo and mother through the placenta.
Similar ecological opportunities on the different continents have produced some striking examples of convergent evolution in mammals.
Section 32-3: Primates and Human Origins
In general, primates have binocular vision, a well-developed cerebrum, fingers and toes, and arms that rotate in their joints.
Primates that evolved from two of the earliest ancestral branches look very little like typical monkeys and are called prosimians. Members of the more familiar primate group that includes monkeys, apes, and humans are called anthropoids.
Today, most paleontologists agree that the hominid fossil record includes at least five genera—Ardipithecus, Australopithecus, Paranthropus, Kenyanthropus, and Homo—and as many as 16 separate hominid species. This diverse group of fossils covers roughly 4.5 million years.