The placenta is what keeps the calf alive during pregnancy

But despite these similarities,these creatures also have many biological differences,and one of the most remarkable is how they give birth.Let's start with the most familiar,placental mammals.This group includes humans,cats,dogs,giraffes,and even the blue whale,the biggest animal on Earth.Its placenta, a solid disk of blood-rich tissue,attaches to the wall of the uterus to support the developing embryo.The placenta is what keeps the calf alive during pregnancy.