Eutheria refers to a group of mammals known as placental mammals. These animals give birth to relatively well-developed young, which are nourished during gestation through a complex placenta. This adaptation allows for longer gestation periods and more advanced development before birth compared to other mammal groups, such as Marsupialia. Eutherians include a wide variety of species, ranging from humans and dogs to whales and elephants. They are characterized by their diverse sizes, habitats, and reproductive strategies. This group plays a significant role in ecosystems around the world, contributing to biodiversity and ecological balance.