Ability to regenerate limbs traces back at least 300 million years

Kai Nungesser

Ability to regenerate limbs traces back at least 300 million years

Researchers have found the earliest evidence for limb regeneration in the fossil record. Rocks unearthed in southwestern Germany have captured 300-million-year-old relatives of the salamander that have one or more regrown limbs. Unlike humans—who can only replace lost fingertips—salamanders are the only modern four-legged animals, or tetrapods, that maintain the ability to regenerate entire limbs throughout their lives. If tissue has been severely damaged or if the wound heals poorly, however, the regrown limb may grow back incorrectly. Such deformities can be quite common, especially if the same limb is repeatedly amputated or injured, leading to regenerated limbs with extra, missing, or fused-together digits in distinctive and unique patterns. In their new paper, published online today in the Proceedings of the Royal Society B, the researchers report identifying these same types of deformity in exceptionally well preserved fossils of the early amphibian, Micromelerpeton (pictured, with an extra, partly fused digit, second from the top). The finding shows that the constant ability to regenerate whole limbs is not unique to modern salamanders, contrary to traditional assumptions. The researchers suggest that this process may have a shared genetic basis that evolved early in the amphibian lineage (and was lost or modified in later species with limited or no regenerative ability), and that part of this foundation may even be a primitive characteristic of tetrapods in general.