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Regeneration was once widespread: ancient amphibians regrew limbs like salamanders do.

Losing a limb or a tail isn't too worrisome for salamanders. They can regenerate lost appendages. And so could a number of their ancient relatives, a new study finds.

Amphibian fossils from 290 million years ago show signs that the animals regrew limbs, researchers report online October 26 in Nature. The findings suggest that some salamander relatives had the ability to regenerate body parts nearly 80 million years before the first salamander existed.

The results "show that salamanderlike regeneration is not something that is salamander-specific, but was instead widespread in the evolutionary past," says Nadia Frobisch, a paleontologist at the Museum of Natural History in Berlin.

Sea stars, frogs and even humans (in the liver, for example) have some degree of regenerative ability at various life stages.

But salamanders are the only four-legged animals that can fully regenerate entire limb bones, nerves and muscles throughout their lifetimes.

When other animals develop arms and legs, hand and feet bones on the outside edge form first. In salamanders, it's the opposite--the thumb before the pinky.

Fossils of various types of amphibians show a similar pattern, suggesting these animals had salamander-like regenerative abilities, Frobisch and colleagues report. The new study builds on Frobisch's previous work with a single species of ancient amphibian that showed the kind of limb abnormalities also seen in modern salamanders that are growing a new limb.

A separate new study shows a molecular basis for the odd way that salamanders regenerate limbs. During early regenerative growth, genes called orphan genes are active, Anoop Kumar of University College London and colleagues report October 26 in Nature Communications. Some of these genes are also crucial in digit formation in amniotes, a group including reptiles, mammals and birds but not amphibians.

Only a few amniotes--like lizards that can regrow their tails--have any type of regenerative powers.

Finding evidence that regeneration was widespread among amphibians in the past is significant, says Hillary Maddin, a paleontologist at Carleton University in Ottawa.

"It suggests that we, and maybe amniotes in general, are much more alone in the lack of an ability to regenerate limbs," she says. "It becomes tempting to think that amniotes are hiding a latent capacity to perform complex regeneration, and the correlation with a potential molecular mechanism, orphan genes, points to a good place to start."

Caption: After studying fossils of extinct amphibians like this one, scientists concluded that some salamander relatives could regrow limbs millions of years ago.


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Title Annotation:LIFE & EVOLUTION
Author:Samoray, Chris
Publication:Science News
Article Type:Report
Geographic Code:4EUGE
Date:Nov 28, 2015
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