The Case of the Missing Lungs

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When earthlings came out of the water and started walking on terra firma some 365 million years ago, their bodies adapted to their new living conditions. Lungs were one of the innovations of that period, allowing animals to survive on the oxygen found in the air.

Some rare species of tetrapods – animals that have four limbs – have since lost their lungs. And for over a decade, scientists thought that the Borneo flat-headed frog was among those that did.

That was the conclusion of a team from the University of Singapore who in 2008 dissected specimens of what’s scientifically known as Barbourula kalimantanensis, an endangered species of frogs that thrives on the Indonesian part of the island of Borneo.

Their analysis found no trace of lungs and suggested that the frogs had lost their lungs to adapt to the cold, fast currents where they live.

David Bickford, who led the study, had told National Geographic this was an “evolutionary enigma.”

Now, 16 years later, researchers from the Florida Museum of Natural History established that B. kalimantanensis did, in fact, have lungs.

In their study, they used a high-resolution micro-CT scanner to analyze the frogs’ soft tissue. There, they found a glottis and very small lungs.

When inflated, the lungs are “substantially smaller than your pinky fingernail,” lead author David Blackburn told Popular Science.

The size of the lungs implies that the animals mostly rely on other ways to extract oxygen, namely through their skin when they’re underwater, the study said.

Bickford said he agreed with Blackburn’s conclusions, and added that he was “very happy” that new discoveries were made on B. kalimantanensis.

The recent findings were made possible by technological advances, analysts added. Bickford explained that in 2008, he and his team could only use “histology (the study of cells and tissues through a microscope) and gross physical dissections.”