Say you've managed to get your hands on Dr. Who's Tardis time machine and decided to give it a whirl. Punching in numbers at random, you end up spinning back some 47.5 million years and landing at the seashore in prehistoric Pakistan. There you spot an enormous, horrifying creature waddling out of the water looking like a crocodile/pterodactyl hybrid.
But this is no lizard: It's an ancient mammal, which it soon proves by giving birth to a miniature version of itself. The babe comes out head-first, snapping the big teeth that line its long, predatory jaws.
While some modern whales, like orcas, have teeth, most sport baleen for sieving krill, and all of them are born tail-first. But back in the Eocene, Maiacetus inuus babies came out head-first with well-developed chompers, ready for battle. Maiacetus means "mother whale," and we know about their babies because in 2000, paleontologists found the fossil of a female M. inuus in Pakistan. Not only was the fossil intact, but there was a fetus in her belly with impressive teeth, poised to emerge snout-first.
Paleontologists also know that this early cetacean species was amphibious, stumping across the shoreline on stubby legs and paddling ominously through the shallows, still dividing its time between land and sea [source: National Science Foundation].