Why has no tetrapod re-evolved gills?

(writing in progress)

Various lineages of tetrapods, after extensive modification for terrestrial life, have evolved to re-enter the water (foraging entirely underwater).

These include

• Serpentes (https://en.wikipedia.org/wiki/Sea_snake)
• Sauropterygia
• Ichthyopterygia
• mosasaurs
• Hupehsuchia
• Pleurosauridae
• Thalattosauria
• Thalattosuchia
• Chelonia
• mustelid Carnivora https://en.wikipedia.org/wiki/Enhydra
• Sirenia https://en.wikipedia.org/wiki/Sirenia
• Cetacea
• Sphenisciformes

All of these forms have evolved streamlining and fin-like flippers. However, all retain lungs, and none has re-evolved gills.

Therefore, all aquatic tetrapods are limited by the need to return to the surface each time they inhale.

Why have gills not re-evolved?

Publicerat 24 augusti 2023 05.35 av milewski