This condition, called neoteny, means it keeps its tadpole-like dorsal fin, which runs almost the length of its body, and its feathery external gills, which protrude from the back of its wide head.

Like most amphibians these begin life in a juvenile "tadpole" state, then metamorphose into the adult form — except for one species, the axolotl, which famously lives its entire life as a juvenile.

The unusual shape of the fuselage — Airbus' "Concept Plane" looks something like a flying tadpole — will also reduce fuel consumption significantly.