Scientists said that they have figured out that the enamel that covers our teeth was originated in the scales of ancient fish. They found this by examining the fossils of long-dead fish and the DNA of a range of creatures existing today.

A report on the new discovery was published online on Wednesday by the journal Nature. Enamel is our body's hardest tissue, composed almost all of calcium, phosphorus and other minerals. Enamel shields teeth while chewing and protects them from pain when encounter very cold or very hot things.

Enamel is present in almost all four-limbed creatures like mammals, birds, amphibians and reptiles. It is also present in so-called lobe-finned fish, some of which evolve and start walking and living on land.

There are some kinds of primitive fish which have similar types of tissue that cover the exterior of their bodies, whereas some have enamel-like substances on their exterior and on parts of their teeth.

The genes required in making such kind of hard tissues are mainly the same, and most of them are clustered together in the genome.

The researchers compared the teeth and outer skeletons of a number of groups of fish and determined that enamel first arose in fish that had skeletons made up of bone, whereas, other fish, such as sharks and rays, have skeletons made of cartilage.

Then, the researchers turned their attention to a fish species, known as Psarolepis romeri, which used to roam in present-day China nearly 445 million to 420 million years back. The fish intrigued the researchers because it was among the oldest species known to sport enamel.