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Amphibian Fossils Suggest Ancient Four-Legged Vertebrates Can Regrow Their Limbs

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New research found that ancient four-legged animals may have possessed the ability for full limb and tail organ regeneration seen only in salamanders.

Salamanders are the only modern tetrapods or four-legged vertebrates that can regenerate their limbs, tails, and internal organs lost or injured in their lifetime.

During embryogenesis, their fingers also develop in “a reversed order” compared to others of their kind - a puzzle for scientists for over a century now, said the study’s first author Dr. Nadia Fröbisch.

Writing in the journal Nature and using new data from fossils, paleontologists from the Museum für Naturkunde Berlin, the State University of New York at Oswego and Brown University sought to study salamanders’ unique limb development and discover its evolutionarily connection with their high regenerative abilities.

Previous research suggested that limb development in the amphibian may be key in its unique ability, such as its first and second digits forming prior to others. In a 2013 study of the axolotl, an aquatic salamander, immune cells known as macrophages were seen to be a critical part of the early phase of limb regeneration.

However, it’s not just salamanders’ limbs that have the capacity to regenerate. Co-author Dr. Constanze Bickelmann explained that compared to lizards whose tails can be regenerated once or twice and merely replaced by a cartilaginous rod, salamanders reproduce a “genuine tail” that includes the neural spine, associated muscles, and other vertebral factors.

The team analyzed different amphibians from the Carboniferous and Permian periods (300 million years ago), deriving the fossils from the collections of natural history museums in the world. It found that various fossil tetrapod groups were able to regenerate their tail and legs, something previously thought to be exclusive to modern salamanders.

Such regenerative ability is likely more prevalent, even representative, among primitive tetrapods. The authors said they were lost in the course of the evolution probably multiple times independently, including the lineage that produced today's mammals. 

They said a large number of individuals at various developmental stages represented the fossilized amphibians – an “extraordinary fossil record” allowing for a detailed study of the evolution of the regenerative capacity.

The findings are hoped to contribute to biomedical studies and possibilities such as one day being able to grow human parts.

Photo: Enrico Strocchi | Flickr

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