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Biol Lett. Aug 23, 2010; 6(4): 509–512.
Published online Feb 10, 2010. doi:  10.1098/rsbl.2009.1033
PMCID: PMC2936207
Air-breathing adaptation in a marine Devonian lungfish
Alice M. Clement1,2* and John A. Long1,2,3
1Department of Sciences, Museum Victoria, GPO Box 666, Melbourne 3001, Victoria, Australia
2Research School of Earth Sciences, Australian National University, Canberra 0200, Australian Capital Territory, Australia
3Natural History Museum of Los Angeles County, 900 Exposition Boulevard, Los Angeles, CA 90007, USA
*Author for correspondence (aclement/at/museum.vic.gov.au).
Received December 10, 2009; Accepted January 14, 2010.
Abstract
Recent discoveries of tetrapod trackways in 395 Myr old tidal zone deposits of Poland (Niedźwiedzki et al. 2010 Nature 463, 43–48 (doi:10.1038/nature.08623)) indicate that vertebrates had already ventured out of the water and might already have developed some air-breathing capacity by the Middle Devonian. Air-breathing in lungfishes is not considered to be a shared specialization with tetrapods, but evolved independently. Air-breathing in lungfishes has been postulated as starting in Middle Devonian times (ca 385 Ma) in freshwater habitats, based on a set of skeletal characters involved in air-breathing in extant lungfishes. New discoveries described herein of the lungfish Rhinodipterus from marine limestones of Australia identifies the node in dipnoan phylogeny where air-breathing begins, and confirms that lungfishes living in marine habitats had also developed specializations to breathe air by the start of the Late Devonian (ca 375 Ma). While invasion of freshwater habitats from the marine realm was previously suggested to be the prime cause of aerial respiration developing in lungfishes, we believe that global decline in oxygen levels during the Middle Devonian combined with higher metabolic costs is a more likely driver of air-breathing ability, which developed in both marine and freshwater lungfishes and tetrapodomorph fishes such as Gogonasus.
Keywords: Dipnoi, air-gulping, Rhinodipterus, Gogo formation, Devonian
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