ANSC 438 Home / Beginning / Milk Composition / Mammary Structure
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The Beginning

Independent Study

The Beginning Module


About 220 million years ago or so, there were highly successful reptile-like species that roamed the earth. This is well before the appearance of dinosaurs. One or more of those reptile-like species had some special properties of their skin. In general these properties were the result of the evolution of some sort of glandular structures in the deep layers of the skin.

These glands secreted some sort of an exocrine secretion. A secretion that was composed mostly of protein and was solid might today be recognized as hair or feathers of mammals and birds, respectively. Other glands may have secreted a viscous oily fluid or a watery fluid with high salt content, today recognized as products of sebaceous glands and sweat glands, respectively.

Another aspect of some of these reptile-like species was that they were probably warm blooded and laid eggs, probably in clutches (several eggs at a time). We would assume that they incubated those eggs with their body heat by laying on them. Some of these were probably proto-mammals, the forbearers of mammals.

Mammalian species all have various skin gland adaptations. Most have hair and many have sweat glands and sebaceous glands. In addition, all mammals have mammary glands.

Which of the following would you not expect to lactate?

The Beginning
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