Limb regeneration in vertebrates evolved 300 million years ago

Scientists have found that the ability of some vertebrates to regenerate or regrow amputated limbs first evolved at least 300 million years ago.
Salamanders are the only modern four-legged vertebrates, or animals that have backbones, able to fully regenerate their limbs into adulthood.
However, other animals, including frogs, caecilians (amphibians that resemble earthworms) and some fish, also have some regenerative capabilities, suggesting the ability may have initially evolved a very long time ago.
To better understand the early evolution of vertebrate limb regeneration, scientists at the Museum fur Naturkunde in Berlin analysed fossils of Micromelerpeton crederni.
Micromelerpeton crederni is a primitive amphibian species and distant relative of modern amphibians that lived during the Upper Carboniferous to Lower Permian time periods, between about 310 million and 280 million years ago.

The fossils were originally discovered in lake deposits in Central Europe, such as Lake Odernheim in southwest Germany, 'LiveScience' reported.

The team found that several of the Micromelerpeton fossils had abnormal limbs. For example, some of the limbs had certain bones fused together. Other limbs had additional toes that were narrower than normal toes. And some limbs had toes with too many or too few bones.
"These same kinds of anomalies typically are observed in response to injury in modern salamanders that are capable of regeneration, both in the wild and in response to experimental amputations in the lab," said David Gardiner, a developmental biologist at the University of California, Irvine, who studies limb regeneration but was not involved in the current research.

The study suggests limb regeneration was an ancient ability present in the amphibian lineage that led to modern amphibians - an ability that salamanders retained.
The ability of modern frogs to regenerate limbs as tadpoles further supports the idea, the researchers wrote in the journal Proceedings of the Royal Society B.
"The similarity between the variant patterns in the limbs of extant salamanders and Micromelerpeton caused by limb regeneration is striking," they wrote.
It is "suggestive of shared molecular mechanisms that are still acting in modern salamanders as they did in their 300-million-year-old relative Micromelerpeton," they wrote.