Can a baby survive if it is not in a yolk sac?

a sac on the newborn snapping turtle to give them nutrients they need

Could possibly be a case of a complete molar/partial molar pregnancy. With a complete molar there will be no baby and the hcg levels rise very rapidly and can get to a very high number. With partial...

baby's survive by their parents looking after them also by telling their parents when they need something.

it's like a packed lunch from your mom. it's the young or newborn's food supply for a few days or so.

yep. Her name is renesmee, and she grows up much faster than any other child.