An international team of paleontologists has solved some of the mysteries surrounding large spiral fossils of an ancient fish called Helicoprion.
Outdated restoration of Helicoprion (© Staab Studios)
Fossils of this 270-million-year-old fish have long mystified scientists because, for the most part, the only remains of the fish are its teeth because its skeletal system was made of cartilage, which doesn’t preserve well. No one could determine how these teeth – that look similar to a spiral saw blade – fit into a prehistoric fish with a poor fossil record, long assumed to be a species of a shark.
“New CT scans of a unique specimen from Idaho show the spiral of teeth within the jaws of the animal, giving new information on what the animal looked like, how it ate,” said Prof Leif Tapanila of the Idaho Museum of Natural History and Idaho State University, lead author of a paper published in the journal Biology Letters.
“We were able to answer where the set of teeth fit in the animal. They fit in the back of the mouth, right next to the back joint of the jaw. We were able to refute that it might have been located at the front of the jaw.”
Helicoprion specimen preserving cartilages of the mandibular arch and tooth whorl (Leif Tapanila et al)
Located in the back of the jaw, the teeth were ‘saw-like,’ with the jaw creating a rolling-back and slicing mechanism. Helicoprion also likely ate soft-tissued prey such as squid, rather that hunting creatures with hard shells.
Another major find was that this famous fish, presumed to be a shark, is more closely related to ratfish, than sharks. Both of these species are fish with cartilage for a skeletal structure, rather than bone, but they are classified differently.
“It was always assumed that the Helicoprion was a shark, but it is more closely related to ratfish, a Holocephalan,” Prof Tapanila said. “The main thing it has in common with sharks is the structure of its teeth, everything else is Holocephalan.”
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Bibliographic information: Leif Tapanila et al. 2013. Jaws for a spiral-tooth whorl: CT images reveal novel adaptation and phylogeny in fossil Helicoprion. Biol. Lett., vol. 9, no. 2; doi: 10.1098/rsbl.2013.0057
