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February 18, 2011

Frog Teeth

(c) National Geographic
The natural world is filled with vestigal traits: whale hips, snake legs, wisdom teeth, etc. These are unnecessary features that disappear over time through natural selection. Because the features provide no advantage to survival or reproduction, and in some cases may have been a disadvantage, the traits are reduced over numerous generations, and will eventually vanish completely. By a principle known as Dollo's law, once a trait is lost completely, it cannot come back. It is just gone.

However, a new analysis of the frog species Gastrotheca guentheri suggests that, in some cases, lost traits can return. This species is the only one, of the over 6000 described species of frog, to have teeth on the lower and upper jaws. Most frogs only have tiny teeth on the upper jaw, if at all. In fact, based on genetic data, the frog lineage lost teeth over 200 million years ago. So, where did this species get them?

According to the study lead by John Weins of Stony Brook University, G. guentheri redeveloped complex lower teeth about 10 million years ago. It makes sense, with the animal's diet: the frog is carnivorous, and having teeth helps to catch prey. However, this is the only species to evolve this solution to the problem. Most other carnivorous frogs instead develop bony pegs on the lower jaw, rather than true teeth. The case of G. guentheri seems to be in violation of Dollo's law. One possibility that the paper suggested was that there could be a loophole. Most frogs do still develop upper teeth; this species could have just transposed that development onto the lower jaw as well. They would not have had to completely re-evolve true teeth. Still, though, this unusual adaptation is a bit of a mystery. This species is clearly off of the lineage that lost bottom teeth. There are far more common solutions than redeveloping true teeth. It's certainly an interesting evolutionary quirk, and provides new paths for more research into the mechanisms driving evolution.

Source- National Geographic: Frogs Evolve Teeth - Again
For more details, view the original publication.