47 million years ago, whales that looked like this gave birth on land, according to a study published this week that analyzes the fossil of a pregnant whale found in the Pakistani desert. This type of ancient proto-whale was amphibious.
When the fossil was discovered, the scientists were perplexed by the jumble of adult and fetal-size bones. First they found small teeth, then ribs going the wrong way. The head-first postion of the fetus gave them the clue: land mamals are generally born head first, and marine mammals are born tail first.
Illustration courtesy John Klausmeyer and Bonnie Miljour/University of Michigan Museums of Natural History.