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Why do salamander larvae have external gills?

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Study an amphibious tiger salamander of the mole salamander family Ambystomatidae in its natural habitat — Caudata Tiger salamanders (*Ambystoma tigrinum*) are widespread across much of the United States. Although they are generally black with yellow blotches, bars, spots, or even stripes, some are lighter in colour or have olive markings. Tiger salamanders belong to the mole salamander family, Ambystomatidae.

Salamander larvae possess external gills because they are exclusively aquatic during this stage of their life cycle and require these structures for respiratory gas exchange.12

Along with their thin, gas-permeable skin, these gills allow larvae to extract oxygen from their aquatic environment. As the larvae develop and eventually undergo metamorphosis, these gills are typically resorbed and the gill slits close as the animal transitions toward a more terrestrial existence and develops lungs for air breathing.231

It is important to note that some species exhibit paedomorphosis, a condition where the adult retains larval features, such as external gills, throughout its entire life. Additionally, in the case of the alpine salamander (S. atra), embryos develop enlarged gills while still inside the mother's reproductive tract to facilitate the absorption of nutrients before they are lost shortly before birth.12