Researchers said that the discovery of bone in the jaw of an ancient shark has indicated that modern sharks are far more advanced than thought earlier.

The finding was reported in the journal PLOS one. It has challenged the evolutionary models, and suggested that the animals with the skeletons built of cartilage have evolved into those with more advanced bony skeletons.

Study’s lead author Professor John Long, a palaeontologist of Flinders University, said that fish-like sharks were thought to be ancient because they only had cartilage, and have never evolved to develop the bones.

Professor said that thus they have turned the idea on its head by stating that early fossil sharks actually had bone in their skeleton, but now they have lost it.

Long and his colleagues unearthed the 380-million-year old fossil in 2005, in the Western Australian Kimberley region's Gogo formation. The fossil named Gogoselachus Lynnbeazleyae was the first shark that was found in this area.

Modern sharks have a miniscule amount of bone in the roots of their teeth and they don’t have a single bone in their main skeleton.

Their skeletons instead are made of cartilage, including tiny structures known as tesserae, a soft rubbery tissue that was the ancestor to bones in other animals.

Recently, authors examined the microstructure of the cartilage of Gogoselachus. They used micro CT scanning, and found that the matrix that held the cartilage together in the jaw had bone cells.

Long said that their fossil shark was the first that showed a true cellular matrix made of bone binding the tiny cartilage units together.

Long added, “We're looking at a shark which has actually evolved from something that previously had a lot more bone in the skeleton, and eventually modern sharks would lose that bone and just become entirely cartilaginous”.

Long mentioned that the fossil has given them a window into the evolution of tissues.