There are three living groups of mammals: placental mammals, monotremes, and marsupials. Placental mammals are the largest and best known, using a placenta during gestation. Marsupials do not use a placenta and have a pouch for their young. Monotremes are unique, reproducing using eggs. There are three main living groups of mammals: placental mammals, monotremes, […]

Mammals evolved after the extinction of dinosaurs, with the first true mammals appearing 195 million years ago. There are three major groups: monotremes, marsupials, and placental mammals. Monotremes lay eggs, while marsupials and placental mammals give birth to live young. Placental mammals are the most successful group, with over 5,500 species and a high metabolic […]