Who knows what will be discovered next?
For over 120 years, the origin of whales vexed paleontologists. They were among the strangest of all mammals, creatures completely adapted to the sea with more in common with us than any fish (although at the beginning of the 19th century "common sense" said otherwise), and it was difficult to imagine how they evolved. If Charles Darwin was right and all life had evolved, different evolutionary paths diverging through time, then whales must have had some sort of traceable ancestry.
The discovery of fossil whales like Basilosaurus and Squalodon illustrated that the evolution of whales may have been preserved somewhere in the fossil record, yet they were fully aquatic forms that did little more than point the way towards a terrestrial origin. Seals and sea lions helped to fill the functional gap showing how a terrestrial mammal might have become adapted to the sea, but for decades evolutionists could do little more than speculate on the earliest origin of whales. In 1890, the Neo-Lamarckian paleontologist E.D. Cope was forced to remark, "The order Cetacea is one of those of whose origin we have no definite knowledge."
This blog is a great mix of science and commentary.