We’ve got a splendid new analysis of a southeast Asian artiodactyl from the Thewissen lab that reveals that these little deer-like animals are a sister taxon to whales — so this pushes our understanding of the ancestry of whales yet further back. Carl Zimmer has already described the essentials — I’ll just show a few pictures of the fossils.
If you’re read Zimmer’s At the Water’s Edge, you already know that one of the key diagnostic features of cetaceans is the large auditory bulla at the bottom of the skull. It’s a distinctive bony capsule that contains the ear structures, and which also has a thick, medial lip called the involucrum. Here’s the skull of these fellows, with that bulla marked out for you. This feature was unique to the whales; now we have to include the raoellid artiodactyls.
This is the whole skeleton. It doesn’t look very whale-like, does it? But the bones don’t lie — this is what the ancient ancestor of whales resembled. You can also see a Buell painting of this lovely animal.
Other revealing details: the bones are unusually dense and carry a particular ratio of isotopes that say that Indohyus spent a lot of time in the water — it was a wader that trotted about in the shallows. It was also an herbivore, so the fondness for an aquatic lifestyle came first, then carnivory.
Thewissen JGM, Cooper LN, Clementz MT, Bajpai S, Tiwari BN (2007) Whales originated from aquatic artiodactyls in the Eocene epoch of India. Nature 450:1190-1194.