24 August 2000

Crocodiles have a unique set of "teeth-like" heart valves thought to allow them to stay underwater for extended periods, according to breakthrough University of Queensland research.

In a paper published in the latest issue of prestigious international journal Nature, Zoology and Entomology Department senior lecturer Dr Craig Franklin and University of Goteborg researcher Dr Michael Axelsson describe the extra valves, unique among vertebrates.

The valves, dubbed "cog-teeth valves" by the researchers, divert blood away from the crocodiles' lungs to their bodies and are controlled by the amount of adrenalin in the bloodstream.

"In other words, when the crocodile is relaxed, the absence of adrenalin circulating in its blood system acts to close the cog-teeth valves," Dr Franklin said.

"Further research is needed to discover the purpose of this function but our theory is that it may allow the crocodiles to dive for several hours without needing to resurface to breathe."

The valves, situated in the crocodile's right ventricle, are also present in other members of the crocodilian family including alligators and the caimans, according to Dr Franklin.

The right ventricle in crocodiles can pump blood to the pulmonary artery feeding the lungs as well as to the left aorta which supplies the body. The cog-teeth valve can divert blood going to the lungs back into the body, a phenomenon known as a ?shunt'.

The discovery of the valves greatly increases understanding of the biology and evolution of the crocodilian family.

"These valves represent an absolute evolutionary novelty. They are further proof of the complexity and sophistication of the ?plumbing' and general anatomy of the crocodile family," Dr Franklin said.

"In contrast, mammalian hearts are very inflexible with the blood supply to the lungs a separate activity to that feeding the body."

Funded by a $10,000, Australian Research Council small grant, the discovery is the result of nine years of research and testing involving the design and construction of a state-of-the-art experimental system.

"Crocodiles are an endless source of fascination for people because they are one of the few animals which can still get the better of us. We now know that far from being primitive or basic, their heart is a remarkable machine," Dr Franklin said.

"This discovery is yet another example of the rich research potential offered by Australia's fantastic fauna. I also have students examining a species of frog which can burrow in mud for nine to 12 months a year and a turtle which can breathe through its bottom."

For more information, contact Dr Craig Franklin (telephone 07 3365 2355).