Maiacetus inuus is a a four-legged creature ancestral to modern whales that was recently discovered. Two adult fossils were found in in Pakistan dating close to 50 million years old. One of these fossils are carrying a fetus. The interesting thing is that the fetus was faced head first. This likely means it was born on land, not water – it does an oxygen breathing animal no good to be born head first in water if it needs to get to some air quickly. Modern whales are borned tail first. This conveniently prevents drowning before they are fully born.
This ancestral whale was far smaller than its modern day lineage. It weighed roughly 600-850 lbs and came in near 9 feet long. This makes sense if the animal was to give birth on land (dragging one’s self is more consistent with laying eggs).
Here’s kind of a crappy idea of what it looked like.