: 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
: It allows for the exchange of oxygen, nutrients, and water from the mother to the fetus, while whisking away waste like carbon dioxide. placental mammal
Placental mammals are mind-bogglingly diverse, categorized largely by how they move and eat. : This strategy is physically draining and risky
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 Placental mammals are mind-bogglingly diverse
: We stay in the womb for a much longer period. This allows us to be born more mature and independent.
The defining feature of this group is the placenta, a vascular organ that develops in the mother’s uterus during pregnancy.