03 March 2013

Fossil of Helicoprion Reveals Secrets of Circular-saw like Teeth

An X-ray CT scan of a well preserved fossil of the Helicoprion reveals how the creature really looks like after years of conjecture.

The Helicoprion was a bizarre creature that lived during the Carboniferous Period around 270 to 300 million years ago. It was believed to be part of the shark family. It had a very distinct and unusual feature in that fossils show that its lower jaw had a circular-saw like set of sharp serrated teeth.

There was much debate on how the creature would look like with this set of teeth. The first fossils discovered of the Helicoprion were very incomplete and didn't really indicate how the creature would really look like. Because of that, there were many theories on how this circular set of teeth fit in with the Helicoprion.

There were some that theorized that the teeth were attached and curled up to a tongue like organ that can extend out similar to an elephant's trunk. Other's believe that the teeth were situated inside the creature's mouth. Other's even suggested that the circular groupings were located on the tail of the Helicoprion.

Although some discovered fossils showed hints of cartilaginous tissue, none have included the braincase or postcranial parts of these fish.

Video: Helicoprion

Helicoprion Fossil Reveals Secrets

Scientific American reported recently that based on an x-ray CT scan of a particularly well-preserved fossil unearthed in Idaho in 1950, scientists were able to figure out how the teeth fitted into the Helicoprion's head (see image above). The fossil included 117 teeth, the cartilage on which the teeth were attached and the upper jaw which revealed that the circular feature was part of the animal's lower jaw.

It was suggested that the creature was about four meters long. Further study of the fossil revealed that the arrangement of tissues in the animal's lower jaw, including those previously hidden by the rock that entombs them, definitively shows that Helicoprion is not a shark but part of a group of cartilaginous fish known as chimaera, a lineage that includes species commonly known as ghost sharks and ratfish.

The study, Jaws for a spiral-tooth whorl: CT images reveal novel adaptation and phylogeny in fossil Helicoprion, was reported by the researchers in the journal, Biology Letters.


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