Although body-part regeneration is a common ability throughout the animal kingdom, salamanders are the only tetrapods (four-limbed vertebrates) which can regrow lost limbs in adulthood. Most research of this process has focused on its genetic and molecular mechanisms in living species such as the axolotl Ambystoma mexicanum, so its evolution is poorly understood. Exceptionally well-preserved fossils from the remains of lakebeds in southwest Germany recently provided evidence that their early ancestors may have shared this trait.
The fossilized Micromelerpeton credneri belong to the order Temnospondyli, from which all modern amphibians are widely believed to descend. Some of their hands and feet display deformities such as extra bones or digits, fused bones, abnormally narrow digits, and spur-like branches – similar to those occasionally seen on modern salamanders when regeneration goes awry, indicating that the mechanisms may have changed little over time. Living about 300 million years ago (Upper Carboniferous to Lower Permian periods), they are the oldest amphibians known to regenerate limbs.
Many modern salamander species cannot regenerate limbs. These findings suggest that this lack evolved more recently, offer insights into the more limited regenerative abilities of juvenile frogs and certain fish species, and hint at a heritage which may be more widely shared among our vertebrate relatives.
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