Air-breathing adaptation in a marine Devonian lungfish

Area of Science:

• Paleontology
• Evolutionary Biology
• Vertebrate Paleontology

Background:

• Tetrapod trackways from the Middle Devonian suggest early vertebrate air-breathing.
• Air-breathing in lungfishes is an independent trait, not shared with tetrapods.
• Previous hypotheses linked lungfish air-breathing to freshwater invasion in the Middle Devonian.

Purpose of the Study:

• To identify the evolutionary origin of air-breathing in lungfish (Dipnoi).
• To investigate the environmental drivers for the development of aerial respiration.
• To determine if air-breathing evolved in marine or freshwater habitats.

Main Methods:

• Analysis of fossil lungfish (Rhinodipterus) from marine limestones in Australia.
• Phylogenetic analysis to pinpoint the node of air-breathing evolution.
• Comparison of skeletal characters in extant and fossil lungfishes.

Main Results:

• Fossils of Rhinodipterus from marine deposits indicate air-breathing specializations by the Late Devonian.
• Air-breathing evolved independently in lungfishes, with origins potentially in marine environments.
• Global oxygen decline and metabolic demands are proposed drivers for air-breathing.

Conclusions:

• Lungfish air-breathing originated independently and developed in both marine and freshwater species.
• Environmental factors like low oxygen levels likely drove the evolution of air-breathing.
• This adaptation occurred in lungfishes and tetrapodomorph fishes during the Devonian period.