Whalewolf

Pakicetus inachus is one of those animals you wouldn't expect to be a whale based on its looks: it's a wolf sized carnivore from the Early Eocene, 52 to 48 million years ago, of Pakistan like the name suggests. 
It was first thougt to be a Mesonychid, but after examining its ears a discovery was made. The characteristics in its inner ear are the same of those that are only found in cetaceans. That makes this animal a whale. Its lifestyle however was quite different: first thought to be fully terrestrial, but the placement of its eyes and the osteosclerosis of its limb bones suggests it must've spend a part of its time in the water. This makes the animal able to catch land-based prey, but also fish and other aquatic animals. There's one adaptation it didn't yet have though and that's being able to hear underwater. The outer ears were still the same as those of terrestrial mammals.

However Pakicetus wasn't alone, there were other animals that filled in the same niche too so competition would be present: www.youtube.com/watch?v=kGTJ4C…


NOTE: The proportions are quite inaccurate here. The body should be quite longer, this is too dog-like.