Helicoprion

Name: Helicoprion ‭(‬Spiral saw‭)‬.
Phonetic: Hel-e-co-pree-on.
Named By: Alexander Petrovich Karpinsky‭ ‬-‭ ‬1899.
Synonyms: Lissoprion.
Classification: Chordata,‭ ‬Chondrichthyes,‭ ‬Eugeneodontida,‭ ‬Agassizodontidae.
Species: H.‭ ‬bessonovi‭ (‬type‭)‬,‭ ‬H.‭ davisii,‭ ‬H.‭ ‬ergasaminon,‭ ‬H.‭ ‬ferrieri,‭ ‬H.‭ ‬mexicanus,‭ ‬H.‭ ‬nevadensis,‭ ‬H.‭ ‬svalis.
Diet: Carnivore/Picivore.
Size: Uncertain but more recent estimates place larger Helicoprion at up to about 7.5 meters long. Many specimens are from smaller indviduals of about 3-4 meters long, suggesting a size variation between species.
Known locations: Australia - Wandagee Formation, Canada, Alberta - Ranger Canyon Formation, British Columbia - Fantasque Formation, Nunavut - Assistance Formation, China - Qixia Formation, Japan - Ochiai Formation andYagihawa limestone Formation, Kazakstan, Mexico - Patlanoaya Formation, Russia, USA, California - Goodhue Formation, Idaho - Phosphoria Formation, Montana - Phosphoria Formation, Nevada - Antler Peak Formation, Texas - Bone Spring Formation, Skinner Ranch Formation, Utah - Phosphoria Formation, Wyoming - Phosphoria Formation. The broad distribution of fossil locations suggests a global distribution.
Time period: Artinskian of the Permian through to the Carnian of the Triassic.
Fossil representation: Mostly only known from the‭ '‬tooth-whorls‭',‭ ‬at least one specimen has been preserved with crushed cartilage from the skull and jaw.

       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 majority of the 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,‭ though for a long time not everyone agreed with the exact location.‭ ‬If the whorl was 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.
       Then in‭ ‬2013‭ ‬a new study by Tapanila,‭ ‬Pruitt,‭ ‬Pradel,‭ ‬Wilga,‭ ‬Ramsay,‭ ‬Schlader and Didier was published,‭ ‬and this was a watershed moment in the study of Helicorpion as this was the first time that something other than the tooth whorl was studied‭; ‬crushed cartilage that once formed the head and jaw.‭ ‬Although incomplete,‭ ‬the cartilage which was on a fossil found in Idaho in‭ ‬1950‭ ‬and officially described in‭ ‬1966,‭ ‬was completely revealed by a CT scan which then enabled the researchers to use computer modelling to form a reconstruction of Helicoprion.‭ ‬This study led to a new depiction of Helicoprion with a tooth whorl within a shorter lower jaw.

       How Helicoprion used its whorl has also been another matter of debate with a variety of theories ranging from the whorl being used as a lash against fish,‭ ‬to a rasp that cut its way through the shells of ammonites with a sawing motion.‭ ‬However even a casual look at the fossil tooth whorls reveals that the teeth have a surprising little amount of wear,‭ ‬and since Helicoprion and relative genera are not thought to have had such a fast replacement of teeth modern day sharks,‭ ‬there is now new speculation that Helicoprion were predators of soft bodied organisms such as molluscs,‭ ‬especially cephalopods such as octopuses.
       It may now only be a matter of time before more cartilaginous remains of Helicoprion are discovered, as other creatures with cartilaginous remains from genera such as Cladoselache, Fadenia and Stethacanthus amongst a growing number of many others are being found.

Further reading
- Ueber die Reste von Edestiden und die neue Gattung Helicoprion. - Verhandlungen der Kaiserlichen Russischen Mineralogischen Gesellschaft zu St. Petersburg, Zweite Series 36:1-111 - A. Karpinsky - 1899.
- A new genus and species of fossil shark related to Edestus Leidy. - Science 26(653):22-24 - O. P. Hay - 1907.
- Helicoprion ivanovi, n. sp. Bulletin de l'Academie des Sciences de Russie 16:369-378 - A. Karpinsky - 1922.
- Helicoprion in the Anthracolithic (Late Paleozoic) of Nevada and California, and its stratigraphic significance. - Journal of Paleontology 13(1):103-114 - Harry E. Wheeler - 1939.
- Helicoprion from Elko County, Nevada. - Journal of Paleontology 29 (5): 918–919. - E. R. Larson & J. B. Scott - 1955.
- New investigations on Helicoprion from the Phosphoria Formation of South-east Idaho, USA. - Kongelige Danske Videnskabernes Selskab, Biologiske Skrifter 14(5):1-54 - S. E. Bendix-Almgreen - 1966.
- The first record of Helicoprion Karpinsky (Helicoprionidae) from China. - Chinese Science Bulletin 52 (16): 2246–2251. - Xiao-Hong Chen, Long Cheng, Kai-Guo Yin - 2007.
- The Orthodonty of Helicoprion. - National Museum of Natural History. Smithsonian Institution. p. 1. - Robert W. Purdy - 2008.
- A new specimen of Helicoprion Karpinsky, 1899 from Kazakhstanian Cisurals and a new reconstruction of its tooth whorl position and function. - Acta Zoologica 90: 171–182. - O. A. Lebedev - 2009.
- Jaws for a spiral-tooth whorl: CT images reveal novel adaptation and phylogeny in fossil Helicoprion. - Biology Letters 9 (2): 20130057 - L. Tapanila, J. Pruitt, A. Pradel, C. D. Wilga, J. B. Ramsay, R. Schlader & D. A. Didier - 2013.
- Unravelling species concepts for the Helicoprion tooth whorl. - Journal of Paleontology. 87 (6): 965–983. - L. Tapanila & J. Pruitt - 2013.
- Eating with a saw for a jaw: Functional morphology of the jaws and tooth-whorl in Helicoprion davisii: Jaw and Tooth Function in Helicoprion. - Journal of Morphology. 276 (1): 47–64. - Jason B. Ramsay, Cheryl D. Wilga, Leif Tapanila, Jesse Pruitt, Alan Pradel, Robert Schlader, & Dominique A. Didier - 2014.
- Saws, Scissors, and Sharks: Late Paleozoic Experimentation with Symphyseal Dentition. - The Anatomical Record. 303 (2): 363–376. - Leif Tapanila, Jesse Pruitt, Cheryl D. Wilga & Alan Pradel - 2020.

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