Science / Medicine : Eardrum Theory Put in Doubt

Fossils recently discovered in east Greenland indicate that the earliest known land vertebrates may have breathed through their ears, according to paleontologist Jennifer Clack of Cambridge University. The discovery contradicts the accepted view that the first land animals with backbones had an eardrum, a feature that all modern amphibians, birds, reptiles and mammals were thought to have inherited directly.

The new findings were based on a large group of fossils found by a 1987 English-Danish expedition to east Greenland, an area that was once a lush tropical forest. Clack said the fossils included the largest samples ever found of Acanthostega, a 360-million-year-old creature about the size and shape of a modern newt.

Other backboned animals from the same period had an eardrum connected to the inner ear by a thin rod which scientists thought conducted sound. They also believed the eardrums were housed in notches on each side of the skull. Clack said Acanthostega had the same notches but its rods, which were thick and plate-like, were unsuitable for conducting sound, suggesting that the notches did not house eardrums but instead supported small openings through which the animal breathed.

The rods could have been used as pump handles powering the breathing movements, an arrangement still found today in some primitive fish.