Hello @mobbs
Very detailed historical account of development of placenta!
Modern fully placental mammals did away with useless egg sacs - they are still there, but more or less vestigial - and instead utilised and re-purposed the equivalent parts of the complex eggs used in the rest of the land animals at this point; the chorion that previously lined the egg shell to allow gas exchange became the placenta, and the allantois eggs used to use as a waste depository became... can you guess? ... The umbilical cord!
It is interesting to get to know the different stories of nature inspired tinkering and manipulations that eventually give rise to what we have today. Who knows where these ever dynamic processes are headed? Evolutionary forces may one day tinker with what we have today...or what do you think?
Regards
@eurogee of @euronation and @steemstem communities
Oh evolution hasn't stopped nor slowed down. We just can't tell because it's such a slow process over millions of years. We are definitely changing! Maybe we'll start laying eggs again in the future...
Did I hear you say lay eggs??😰
As a mother I think laying an egg would be sooooo much easier ;P