Cases of Tail Regeneration and Bifurcation in the Endangered Mongolian Racerunner (Eremias argus Peters, 1869) from the Sindu Coastal Sand Dune, Republic of Korea

Tail autotomy is a key antipredator adaptation in lizards, allowing individuals to evade predation by voluntarily shedding part of their tail. Because the tail serves vital functions in locomotion, energy storage, and social signaling, effective regeneration follow- ing autotomy is essential for maintaining overall fitness and survival. Such tail regeneration is also likely to occur in lacertid lizards inhabiting the Republic of Korea; however, it has not been specifically addressed yet. Here, we present field observations of tail re- generation and bifurcation in the endangered Mongolian racerunner (Eremias argus) in the Republic of Korea. One individual was ob - served to have regenerated most of its tail within 49 days following tail autotomy. Another individual exhibited a bifurcated tail, which is presumed to have resulted from an abnormal regenerative process. This study documented, for the first time, tail regeneration rate and morphological abnormalities in E. argus tail in the Republic of Korea. The findings provide valuable insights into the re- generative biology of the species.