Known as cartilaginous fish – which means their skeletons are not made of bone, but cartilage – sharks were generally understood to have not evolved their own bodies. Typically, it was believed that fish with cartilage would eventually see their skeletons evolve into bone, something that – until recently – did not happen with sharks. Yet, this long standing belief was torn apart thanks to the bombshell find of a 380-million-year-old shark, which seemed to have pieces of bone cell within its cartilage-based skeleton.
Reports say that fossil evidence for sharks can be traced back to around 450 million years ago, while the first shark teeth found dated back 400 million years ago.
But the study released in Nature Ecology & Evolution Monday, saw scientists reveal the fossilised fish discovery related to both sharks and animals with bones.
The shark, found in 2015, was located in Mongolia, and according to Newsweek is called Minjinia turgenensi.
Dr Martin Brazeau, lead author of the study from Imperial College London, said the find was “a very unexpected discovery”.
He added: “Conventional wisdom says that a bony inner skeleton was a unique innovation of the lineage that split from the ancestor of sharks more than 400 million years ago, but here is clear evidence of bony inner skeleton in a cousin of both sharks and, ultimately, us.
“If sharks had bony skeletons and lost it, it could be an evolutionary adaptation.
“A lighter skeleton would have helped them be more mobile in the water and swim at different depths.
“This may be what helped sharks to be one of the first global fish species, spreading out into oceans around the world 400 million years ago.”
The scientists explained that this could mean that sharks may have originally had a bony skeleton, before evolving into a more favourable cartilaginous one.
Researchers say this may show that they may have redeveloped, as opposed to maintaining the same cartilage-based skeleton for its history on Earth.
They are hoping that more fossil samples can be found, as they currently only have the find they made five years ago as evidence.
The authors added in their report: “Continued work in Mongolia and re-evaluation of phylogenetic datasets will be necessary to address this, with the results likely to lead to substantial re-evaluation of gnathostome [evolutionary history].”