If you are still coming to terms with the concept that monkeys are our ancestors, then you will be surprised to see a lungfish in the family tree.
The lungfish occupies a unique place in evolution, some experts believing it to be a link between the fishes and the land animals. Aside from the fact that it possesses a lung allowing it to breathe air, the lungfish secretes hormones to stimulate reproduction which are identical with those of mammals, including humans. This discovery was made by Professor Jean Joss who heads the Australian Lungfish Research Centre based at Sydney’s Macquarie University.
While a lungfish breathes mostly through its gills, it can surface and breathe with the lung if the water has inadequate oxygen. Lungfish also have internal nostrils, (different to fishes which have external nostrils) and this provides another link to land animals.
About 350 million years ago the Queensland lungfish was one of seven lungfish species inhabiting the Australian continent. Today it is the only surviving Australian species, and one of only six lungfish worldwide.
Now the Australian lungfish is endangered with the natural habitat limited to the Mary and Burnett Rivers between Nambour and Bundaberg in south-east Queensland. They have been introduced to some lakes and reservoirs.
While they grow up to a maximum of 2m (6’8″) and weigh 45kg (99lb), they are usually half that size. They look something like a stout eel with large overlapping scales and a tail which ends in a point. While other lungfish have two lungs the Australian lungfish has only one and is considered the most primitive of the surviving species.
Their fins are also quite different to modern fish being like fleshy paddles which are seen as the beginning of legs. They also feature tiny holes under the jaw which are electro-receptors and sense the presence of live food, such as worms, in the dark. Other animals such as the platypus and shark also have this type of sensory ability. Conversely, like the shark, the lungfish also has a cartilaginous backbone, but sharks are considered to be one lower on the evolutionary scale than modern fishes.
The Australian Museum holds fossilised skulls of the lungfish, Dipnorhynchus, which lived 400 million years ago. These reveal they have changed very little, and still clearly shows the internal nostrils.
Professor Joss is one of the few people legally allowed to keep lungfish as they are a protected species. She fears this legislative protection may actually lead to the species’ loss. If they were allowed to be sold as pets the money made would give them a dollar value and breeding programs may then result.
Further information
Encyclopedia of Fishes (1995), edited by John Paxton and William Eschmeyer, University of NSW Press, features a large section on lungfishes and is available from major bookstores. Rrp $55. It should also be available from most large libraries.