Mammal — Placental

Placental mammals are mind-bogglingly diverse, categorized largely by how they move and eat.

: This strategy is physically draining and risky for the mother, who becomes less mobile and must eat significantly more to support the growing fetus. 3. A Family Tree of Giants and Shrews placental mammal

The Ultimate Insider: Why Placental Mammals Rule the Earth Take a look around. From the dog napping at your feet to the squirrels darting across the park—and even the person reading this—you are surrounded by . Also known as eutherians , this group represents over 90% of all mammal species on the planet. A Family Tree of Giants and Shrews The

: Crucially, it keeps the mother's and baby's blood from mixing. This prevents the mother's immune system from attacking the fetus as a "foreign parasite". : Crucially, it keeps the mother's and baby's

Unlike (who give birth to tiny, underdeveloped "joeys" that must finish growing in a pouch), placental mammals take their time.

While the exact "first" placental is debated, fossil evidence suggests a massive explosion in their numbers shortly after the extinction of the dinosaurs about 65 million years ago. They quickly filled the ecological niches left behind, eventually spreading to almost every habitat on Earth. Quick Comparison: Mammal Reproductive Types Marsupial Monotreme Birth Style Live birth (Mature) Live birth (Underdeveloped) Early Care Internal (Placenta) External (Pouch) Egg Incubation Examples Kangaroos , Opossums Platypus , Echidna