Re-evolution of Teeth in a Frog

Gastrotheca guentheri
Louis Dollo, a French born, Belgian paleontologist is perhaps best known for supervising the reconstruction of Iguanodon fossils discovered in an underground mine in 1878; and for an idea which says, evolution is not reversible. The idea became known as Dollo’s Law and suggests that once organisms loose a structure during the course of evolution it will not re-evolve. Like most such “laws,” it was doomed to failure due to exceptions. John Wiens, Stony Brook University, has now documented the re-evolution of mandibular teeth in the marsupial frog, Gastrotheca guentheri. It has been long known that frogs do not have teeth on the mandible – with the exception of some frogs of the family Hemiphractidae. Weins used a time-calibrated amphibian phylogeny that demonstrates frogs lost their mandibular teeth 230 million years ago (MYA), only to have Gastrotheca gunetheri (or an ancestor) re-evolve mandibular teeth 5 to 17 MYA. George Kingsley Nobel recognized that Gastrotheca had true teeth, he wrote “The most remarkable osteological feature of the Hemiphractinae is the redevelopment of true teeth on the dentary….Such teeth do not occur in any other Sallientia…”

Weins’ results provide an exceptionally well documented example of re-evolution, demonstrating that mandibular teeth were lost in the ancestor of all living frogs and then re-evolved in the hemiphractid species G. guentheri. Weins points out that the re-evolution of mandibular teeth may not surprise herpetologists, but notes this example has been ignored in the recent literature on Dollo's law. The time involved from the loss of teeth to their re-evolution in Gastrotheca – an absence of at least 225 million years (and probably longer) is remarkable.

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Noble, G. K. 1931The Biology of the Amphibia. McGraw-Hill, New York .

Wiens, J. J. 2011. Re-evolution of lost mandibular teeth ion frogs after more than 200 million years, and re-evaluating Dollo’s law. Evolution, doi: 10.1111/j.1558-5646.2011.01221.x

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