The Evolution of Whale’s Tails

PhysOrg.com has an interesting, but ultimately uninformative, write up of some research that will be appearing in the Journal of Vertebrate Paleontology. Here is the context:

The different body forms seen in the lineage of whales point to different methods of swimming underwater. Previous studies have proposed a possible process to evolve from the ancestral form, paddling with all four legs, to the modern-day whale in which the tail oscillates up and down.
Living vertebrates that are capable swimmers employ a whole range of different techniques, including five particularly well-defined methods: quadrupedal paddling, paddling only using the back legs, undulation of the hips, tail undulation, and tail oscillation.
Interestingly, it had been suggested that during whale evolution that each of these steps occurred in turn, but that the hip undulation stage might have been by-passed. The discoveries indicate that the complete opposite was true, and as Uhen says, “wiggling hips were a significant step in the evolution of underwater swimming in whales.”

The discoveries refer to new finds of material attributed to Georgiacetus vogtlensis. Again, from PhysOrg:

In particular, previously unknown bones from the tail show that it lacked tail flukes. On the other hand, it did have large back feet, and Uhen suggests that it used them like modern whales use their tail flukes. Undulating, or moving the body in a wave-like fashion, was a key factor in the evolution of swimming.

You can see what the skeleton of G. vogtlensis looks like here.

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3 Responses

  1. National Geographic also has a report on this:
    http://news.nationalgeographic.com/news/2008/09/080911-whale-legs.html

  2. I don’t know what you found unenlightening — I thought it was pretty interesting, myself. I had read several years ago that the original animal from which whales evolved was rather like a bear. This Vogtle Whale (Georgiacetus vogtlensis) seems well adapted to the water, much more like a dolphin, but still with legs and sharp teeth, and its blowhole is on the tip of the snout instead of the top of the head. It’s a good transitional form, I should say. Later, the back legs become vestigial before disappearing altogether, and the fluke evolves out of the tail, I gather — or does it come from the merger of the back feet like in the seals? I can’t quite tell from the series of whales shown in the first illustration. Clearly the front feet became flippers. And the blowhole migrated to the top of the head, while the teeth evolved into something completely different.

  3. The PhysOrg piece doesn’t offer much in the way of detail, which is why I say ultimately uninformative. The National Geographic piece is much better.

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