Are pigs and/or hippos related to whales?

Ok, ok, I know, another blog on whales but what can I say, I love whales. But anyway…

Jessica Theodor, an associate professor in the Department of Biological Sciences at the University of Calgary, and her colleague Jonathan Geisler, associate professor at Georgia Southern University were disputing a study that created a different family tree for the hippo. That research was published in Nature in December 2007 by J. G. M. Thewissen, a professor at Northeastern Ohio Universities College of Medicine, and his colleagues. Thewissen says that whales are more closely linked to an extinct pig-like animal, often known as India’s pig or Indohyus, while hippos are closely related to living pigs.

What Thewissen was saying is that Indohyus is the closest relative of whales – and I agree. But where I believe he is wrong, is that he is saying that that hippos are more closely related to true pigs than they are to whales.  This contradicts most of the data from DNA from the last 12 or 13 years. Those data place hippos as the closest living relative to whales.

The controversy began after the new fossil of Indohyus, was discovered and written about by Thewissen and his group. This animal lived around 48 million years ago, lived in the water and fed on land.

When biologists study family trees, they traditionally rely on morphology, in other words, the shape of bones. More recently, the DNA revolution means that scientists can use DNA data as another tool to reconstruct family trees, but DNA data can’t be used all the time because DNA is not available for most fossils. “In order to get the best understanding, researchers combine the two sources of data in a single analysis. But what Thewissen and his group did, was leave one of the major ones out,” says Theodor.

Before the widespread use of DNA data, hippos had been thought to be closely related to pigs, but DNA data show that whales are closely related to hippos. Geisler and Theodor argue that leaving out the DNA data not only ignores important information, it implies that the evolution of swimming evolved independently in hippos and whales, when it may have evolved only once in a common ancestor. Your Thoughts?


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