Scientists have discovered an ancient vestigial lung in the rare coelacanth, filling in the gaps of lineage in the rare fish as to what it may have looked like millions of years ago.
All mammals, including humans, are four-legged vertebrates or tetrapods that evolved over the millennia from some ancestral lobe-finned fish.
Some of these fish still exist today including the lungfish and the coelacanth.
The rare and amazing coelacanth was long thought extinct by science until the discovery of Latimeria chalumnae in 1938, a "living fossil" that had retained physical features from long ago.
Now scientists have made a breakthrough discovery in finding a series of bony plates known in the fossil record, but not yet found in a living fish.
Using x-ray tomography, the researchers were able to scan coelacanth of differing age groups and found that early embryonic stages featured a large and potentially functional lung.
Although the lung has no function now, its ancestors probably had a functional, primitive lung.
It's possible that their move, eons ago, into deeper waters ultimately saved the species and made an air-breathing lung unnecessary.