Deformities arise and occur in nature in all species and forms of life.
There was speculation as to cause. My teacher at Mesa College, Erica Specht, taught me that frogs are an indicator species. That's just one of the reasons students of biology dissect frogs. Frogs are the most numerous of the tailless amphibians, and there are over 2,900 species. True frogs, of the family Ranidae, generally spend an equal amount of time in water and on land and breathing air, although aquatic frogs spend most of their time in water.