They’ve been on the planet for around 83 million years, and their giant ancestor Deinosuchus is believed to have even dined on dinosaurs. But while the crocodile is best known as an aggressive apex predator, the reptile has plenty of attack power in its immune system too.

For the first time, scientists have discovered a unique component of a saltwater crocodile’s physiology that helps its immune system identify and kill fungal infections. It’s this that allows them to thrive in microbe- and pathogen-laden waters infection-free, despite frequently sporting wounds from territorial disputes in the wild.

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Researchers at La Trope University in Melbourne, Australia, have isolated a unique pH-sensing mechanism made up of small proteins, known as defensins, that detect infection and alert the immune system. The alarm-sounding role of the defensins is so far unique to these reptiles and hasn’t been identified in any other plant or animal.

Read more: New Atlas