Frogs Evolve Teeth - Again

[Frog News]

National Geographic News (Washington DC, USA) February 10th, 2011 12:09 PM: Frogs Evolve Teeth - Again

Lower-jaw teeth in frogs re-evolved after an absence of 200 million years, a new study says. The discovery challenges a "cornerstone" of evolutionary thinking, according to experts.

Of the more than 6,000 species of frogs, only one, a South American marsupial tree frog called Gastrotheca guentheri, has teeth on both its upper and lower jaws. Most frogs have only tiny upper-jaw teeth.

A new analysis of the frog family tree reveals that the common ancestor of frogs, which long had lower-jaw teeth, lost them more than 230 million years ago before eventually going extinct.

The marsupial frog G. guentheri didn't have lower teeth, then "boom, around 5 to 15 million years ago, it got them ... ," said John Wiens, who authored a recent study on the phenomenon.

The discovery runs counter to a principle called Dollo's law, which states that physical structures lost during evolution are never regained, according to Wiens, an evolutionary biologist at Stony Brook University in New York State.

In fact, the teeth's reappearance may have exposed the law's loophole: That it's "much easier to re-evolve things if you're already making them somewhere else," Wiens said.

In other words, the frog "didn't have to make teeth on the lower jaw from scratch, because they're already making them on the upper jaw."

Continued in Full Article