The axolotl, sometimes called the Mexican walking fish, is a cheerful tube sock with four legs, a crown of feathery gills and a long, tapered tail fin. It can be pale pink, golden, gray or black, speckled or not, with a countenance resembling the “slightly smiling face” emoji. Unusual among amphibians for not undergoing metamorphosis, it reaches sexual maturity and spends its life as a giant tadpole baby.

According to Aztec legend, the first of these smiling salamanders was a god who transformed himself to avoid sacrifice. Today, wild axolotls face an uncertain future. Threatened by habitat degradation and imported fish, they can only be found in the canals of Lake Xochimilco, in the far south of Mexico City.

Captive axolotls, however, are thriving in labs around the world. In a paper published Thursday in Genome Research, a team of researchers has reported the most complete assembly of DNA yet for the striking amphibians. Their work paves the way for advances in human regenerative medicine.

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Many animals can perform some degree of regeneration, but axolotls seem almost limitless in their capabilities. As long as you don’t cut off their heads, they can “grow back a nearly perfect replica” of just about any body part, including up to half of their brain, said Jeramiah Smith, an associate professor of biology at the University of Kentucky and an author of the paper. To understand how they evolved these healing superpowers, Dr. Smith and his colleagues looked to the axolotl’s DNA.