Sharks as Advanced as Humans in Evolutionary Terms

It has long been thought that the shark was an evolutionary throwback, a fish that hadn’t changed in about 400 million years. However, the discovery and study of a fossil dating back 415 million years shows that this preconception is wrong. The tiny fish skull from Siberia is only two centimetres, and was originally discovered in the 1970s. It offers hints about the origins of all jawed vertebrates.  

There are two different types of jawed vertebrates, bony ones and cartilaginous ones. Bony fish are the ancestors of all jawed invertebrates, on land and sea, and cartilaginous fish are the ancestors of fish such as sharks and rays. However, there was a common ancestor of both bony and cartilaginous fish.

The Siberian fossil is a relation of that common ancestor, revealing characteristics of both bony fish and cartilaginous fish. It was originally classified by scientists in the 1970s as a bony fish, but using a CT scanner to look at the skull, they discovered characteristics of cartilaginous fish too.

The skull was still embedded in rock, so Sam Giles, the study's lead researcher and a paleobiology doctoral candidate at Oxford University, used the CT scanner to create a 3D model. Using this model, they discovered that the fish has a sensory line canals on its skull, the same as bony fish today use to detect changes in pressure around them to help them avoid predators.

However, it also has characteristics of a fish made of cartilage. It has blood vessels at the bottom of its skull is similar to what you might see in a cartilaginous fish.

The idea that sharks are primitive stems from the fact that scientists believed that the common ancestor of bony and cartilaginous fish had more cartilage than bone. If this is true then the cartilaginous fish have not evolved as much as bony fish. However, this fossil tells us that the last common ancestor had lots of bone, which means that sharks are very highly evolved creatures.

Another piece of evidence in the case for sharks as evolved creatures is a newly discovered shark-like fish fossil. It is 325 million years old, and has arches in its jaws, which bears no resemblance to modern sharks and instead looks like a bony fish. This suggests that modern sharks are very specialised.