Helicoprion

Name: Helicoprion ‭(‬Spiral saw‭)‬.
Phonetic: Hel-e-co-pree-on.
Named By: A.‭ ‬P.‭ ‬Karpinsky‭ ‬-‭ ‬1899.
Classification: Cordata,‭ ‬Chondrichthyes,‭ ‬Eugeneodontida,‭ ‬Agassizodontidae.
Species: H.‭ ‬bessonovi‭ (‬type‭)‬,‭ ‬H.‭ ‬davish,‭ ‬H.‭ ‬ergasaminon,‭ ‬H.‭ ‬ferrieri,‭ ‬H.‭ ‬mexicanus,‭ ‬H.‭ ‬nevadensis,‭ ‬H.‭ ‬sierrensis.
Diet: Carnivore/Picivore.
Size: Uncertain but estimated between‭ ‬3‭ ‬and‭ ‬4.5‭ ‬meters long.
Known locations: Worldwide.
Time period: Artinskian of the Permian through to the Carnian of the Triassic.
Fossil representation: Only the‭ '‬tooth-whorls‭' ‬have been preserved,‭ ‬although there are an increasing number of these known.

       Helicoprion is one of the stranger sharks in the fossil record,‭ ‬although at the time that Helicoprion swam the oceans there were actually many sharks that did not conform to the‭ '‬standard‭' ‬form that we know today.‭ ‬The only remains of this shark are the teeth which are fossilised in a spiral pattern like the shell of an ammonite,‭ ‬in fact when first discovered these fossils were actually thought to be some kind of exotic ammonite shell.‭ ‬These arrangements of fossil teeth are today referred to as a‭ '‬tooth-whorl‭'‬.‭
       How and where the tooth-whorl attached has been a source of puzzlement to palaeoichthyologists ever since it was realised what it was,‭ ‬and while the obvious choice might be to place the tooth-whorl within the mouth,‭ ‬the whorl has on occasion been placed in different parts including the dorsal fin and even the tail.‭ ‬Today the whorl is almost always placed with the lower jaw,‭ ‬although not everyone agrees with the exact location.‭ ‬If the whorl is mounted on the tip it would significantly increase the drag that Helicoprion experienced as it swam through the water.‭ ‬Not only would it require more effort to swim,‭ ‬the greater water turbulence would have revealed the presence of Helicoprion to its potential prey.‭ ‬This is why many people now consider the whorl to have been further back into the mouth.
       How Helicoprion used its tooth whorl is yet another matter of debate.‭ ‬Some researchers think that it would continually grow during the life course of Helicoprion so that it could progressively feed upon larger prey.‭ ‬Some have suggested that Helicoprion would trap ammonites against its upper jaw and then roll the whorl against the shell to rasp its way through to the soft bodied mollusc within.‭ ‬It has even been suggested that the tooth-whorl was so shaped in order to act like a lure to the mouth of Helicoprion.‭ ‬Other depictions have Helicoprion swimming into a shoal of fish and then extending the whorl and lashing out towards any fish within the vicinity,‭ ‬or even extending it into a toothed lance to stab into the flanks of its prey.
       It is highly unlikely that a more complete fossil of Helicoprion will be found because sharks have cartilaginous skeletons that decompose very quickly.‭ ‬That said it is not completely impossible as other sharks including Stethacanthus and Cladoselache have managed to get themselves preserved with a surprisingly high amount of detail.





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