How does the South American lungfish differ from the Australian lungfish in its gills?

The South American lungfish (Lepidosiren paradoxa) and the Australian lungfish (Neoceratodus forsteri) differ significantly in their reliance on and development of gills for respiration.

• Australian Lungfish: This species possesses well-developed gills that serve as the primary site for oxygen uptake and carbon dioxide elimination under normal conditions, particularly when water is well-oxygenated. Because of this, it relies less frequently on atmospheric air breathing compared to other lungfish species.12
• South American Lungfish: In contrast, the South American lungfish has reduced gills. As a result, it depends heavily on its lungs for ventilation, reflecting a more advanced adaptation toward aerial respiration.1

These differences highlight the evolutionary transition of lungfishes as a group that bridges the gap between water-breathing and air-breathing vertebrates. While the Australian lungfish maintains a lifestyle where gills and lungs work side by side with a primary focus on the former, the South American species has shifted its respiratory dependency toward its lungs.13