Fossils of an ancient relative of modern amphibians reveal that the capacity to regenerate limbs after an injury had already evolved by 300 million years ago. The work was published in Proceedings of the Royal Society B this week.
These days, salamanders are the only tetrapods (4-legged animals like us) that are capable of regrowing their own limbs throughout their lives, sometimes repeatedly if necessary. People can only regenerate lost fingertips and maybe a portion of the liver. Previous work on the mechanisms of regeneration (such as molecular pathways in red-spotted newts) have focused on applying the findings to human medicine. So how regenerative capacity evolved is still a mystery.
Now, a Museum für Naturkunde Berlin team led by Nadia Fröbisch describes a suite of unique patterns of abnormalities in the limbs that are “distinctive of irregular regeneration” in a distant amphibian-relative called Micromelerpeton credneri, which lived during the Late Carboniferous and Early Permian in central Europe.
After examining several well-preserved fossils from lake deposits of the Saar-Nahe Basin in southwestern Germany, the researchers found a number of abnormalities in the hands and feet, including fusions of bony elements, bony spurs, and additional or fewer fingers and toes. Here’s a Micromelerpeton whole specimen from Lake Odernheim:
You can see more examples of abnormalities caused by regeneration here. These kinds of abnormalities, as well as their positions, are very distinct and characteristic for abnormalities that occur in regenerated limbs of modern salamanders. If tissue is severely damaged or if the wound heals poorly, the regrown limb may grow back incorrectly, Science explains. These deformities can be quite common with repeated injuries and amputations.
“Traditionally it was assumed that the capacity to regenerate limbs is something unique to salamanders that likely evolved rather late in their evolutionary history,” Fröbisch says in a news release. Nope. “Regenerative capacity of the limbs and its genetic basis are much older than previously thought.”
That the ability to regenerate limbs is an ancient feature (rather than a derived one) makes you wonder if it could be a primitive trait of all tetrapods. Fröbisch adds: “There is so much left that we can learn from them about ourselves.”
Images: N.B. Fröbisch et al., Proc. R. Soc. B (2014)