The correct answer is Platypus. The Platypus (Ornithorhynchus anatinus) is a monotreme, a group of mammals that lay eggs instead of giving birth to live young. Dolphins, seals, and whales are placental mammals and are viviparous, meaning they give birth to live offspring. Monotremes are the most primitive group of mammals, and the only living examples are the platypus and four species of echidnas. They share characteristics of both mammals (like possessing mammary glands and fur) and reptiles (like laying eggs).