About 200 million years ago, furry little egg-laying creatures evolved the ability to feed their offspring with a secretion from some special glands: milk. Their evolutionary journey continued and by about 160 million years ago, the first mammals with a real placenta had come into being. Instead of laying eggs, they gave birth to live young that had been connected via a placenta directly to their mother during pregnancy, allowing the exchange of oxygen, nutrients and waste products.
These early mammals looked like shrews do today. They were small and had a long body, eyes typical for nocturnal mammals and little spiky teeth for eating insects. But they were not shrews. They were the ancestors of all the placental mammals that exist now, including shrews, bats, elephants and humans.
