Sharks are often seen as "living fossils," examples of evolutionary excellence that have not altered their design since they came into existence. Biologists have theorized that the respiratory system, fed by efficient gills, was present in the species since they first diverged on Earth more than 400 million years ago.
But researchers have recently discovered a fossil record that appears to refute that theory. A study of the 325-million-year-old "shark-like" creature, published in scientific journal Nature, suggests that ancient sharks might have developed their gills after bony fish did.
The authors of the study say the fossil, which represents the earliest identified cartilaginous fish with a preserved respiratory system, has a gill structure more like a modern bony fish than a shark.