Thought about a hypothetical lineage of Whales descended from an Oligocene Hybrid of a Basal Odontocete and a Basal Mysticete that managed to survive into an Alternate Modern Day where Humans died out in Early Pleistocene. The abundance of Krill, Squid and Fish in the Oceans led to a Semi-Aquatic species which developed re-evolved hind-limbs complete with Melon and Baleen evolving on the Swamps of what is the Netherlands to Denmark in our timeline. Pic related is some Miocene Whales of our timeline.