Scientists have unraveled the origins of
Did mammals use to lay eggs?
Despite evidence that the earliest examples of creatures such as mammals and reptiles gave birth to live young, they actually may have laid eggs, a scientist argues. ... The fact that mammals and reptiles wrap their embryos within these defenses makes them known as amniotes, which first evolved about 310 million years ago.
Why did our mammal ancestors stop laying eggs?
Therefore, mammals already had milk before they stopped laying eggs. Lactation reduced dependency on the egg as a source of nutrition for developing offspring, and the egg was abandoned completely in the marsupial and placental mammals in favor of the placenta.
