Placental mammals have a placenta, an organ that develops during gestation and bridges mother and fetus.
The placenta provides nutrients to the fetus to develop in the womb, protecting the baby from the outside world until they are fully developed.
While we don’t know the first placental mammal for sure because of their low preservation potential, we do know that around 55 million years ago, 10 million years after the extinction of the dinosaurs, placental mammals exploded in numbers while marsupials decreased.
Placental mammals have, you guessed it, a placenta, the important organ that develops during gestation and acts as a bridge between mother and fetus. It provides the nutrients that the fetus needs to survive in the womb and allows a species’ young to live inside their mother until such time as they are ready to be born. This means that babies are protected from the outside world until ...
