Last week I wrote about a new study that identified a fossil mammal as the closest relative to whales, helping to shed light on how whales moved from land to sea. The mammal, Indohyus, was a small four-legged creature that probably spent a fair amount of time in water and ate vegetation. The authors of the new study proposed that the ancestors of whales originally lived this way. Gradually, the whale lineage became more adapted to life in water and shifted to eating meat, as exemplified by early whales like Ambulocetus, which was something like a furry alligator.

In the comment thread, Noumenon asked this question:

I don’t understand how Indohyus and Ambulocetus, both dated to around 47 mya,