# Mammal evolution

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Here I want to discuss how mammals evolved. I have always thought that a reptile was forced to hunt at night to avoid predators. Over time its body adjusted and it evolved internal heat known as warm blood.

But I am confused about how mammals evolved to grow their offspring inside thier bodies. Maybe one species left its eggs in its body to keep it warm. Over time the egg evolved into a placenta. Any more ideas of mammal evolution.

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well, there are some reptiles that give birth to live young, and like you said, they incubate the eggs inside their bodies.

so i agree there

i have no idea if you are right about the nocturnal/warm blood thing, but it makes sense.

also, hair probably evolved from scales somehow... probably also to keep warm. it was probably actually a big leap from scales to hair, since small steps would be very inefficient, but i wish i knew exactly what could have happened.

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post #1 I know little to nothing about, but the hair from scales, sure, its made from Keratin, same as our finger and toe nails are made from too

in fact its common practice to grind up fish scales for use in cosmetics as nail varnish/polish, so thats a real full circle in evolution in its own right, girlies protecting/covering nails with the same stuff theyre made from

thats my 2 pennys worth for this thread, I dont know enough about the rest to comment

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I understood that it was most likely to have been predators that developed warm blood first. To survive as a predator, you need to be faster than your prey. Reptile predators couldn't afford to sit around basking to heat their bodies, as by the time they were ready, their prey would also be ready for flight, so they developed a 'pre-heating' system to give them an advantage.

The same kind of mechanism can be seen in (e.g.) the white shark. It is a fish, and cold blooded, but it's principle prey are warm blooded (seals and sea lions), so the white shark had developed a bre-heating system in some of its main swim muscles to give it the burst of speed it needs to catch these fast warm-blooded animals.

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