A Helicoprion whorl. The teeth line the outer edge of the spiral. Photograph by Chip Clark. |
Ever since its discovery, the animal has been shrouded in
mystery. Being known only by these whorls, no one had the slightest idea of how
the rest of Helicoprion looked. Some
even proposed that the coiled teeth may in fact be the shells of ammonites. However, when Alexander Petrovich Karpinsky
coined the name in 1899, he demonstrated that Helicoprion was a sharklike fish rather than a mollusk. His idea
about the function and placement of the whorl on this animal, however, was
completely off.
Former depictions of Helicoprion range from the reasonable to just plain goofy. Artwork by the brilliant artist, a personal favorite of mine, Ray Troll. |
Karpinsky proposed that the whorl was actually located on
Helicoprion’s nose. While this idea
is ridiculous compared to what we now know about this animal, it was nowhere
near the most outlandish, or creative, idea. The whorl has been speculatively
placed everywhere from within the fish’s throat to the tips of its fins and
tail. More recent reconstructions place the whorl in a sort of buzzsaw-like
placement at the end of the lower jaw, which is usually depicted as being
elongate. A new study by Lief Tanapila and Jesse Pruitt agrees with the buzzsaw
placement of the whorl, but it reveals much more about the evolution and
overall appearance of Helicoprion.
Most modern reconstructions display Helicoprion with a buzzsaw-like, elongated jaw. Reconstruction by Dmitri Bogdanov. |
Using CT scans, Tanapila and Pruitt discovered a number
of intriguing features of this fish. While comparing the lower jaw of Helicoprion to a buzzsaw may seem like a
stretch, both the shape and the
function of this dentition was very similar to such a tool. As the jaw closed,
the whorl slightly rotated. Another puzzling discovery was that Helicoprion lacked teeth on its upper
jaw altogether; the whorl was the fish’s only set of teeth. Such adaptations are ideal for a very specialized niche, which we will examine in a couple of paragraphs.
The spotted ratfish, rather than true sharks, is the closest living relative of Helicoprion. Photograph by Dan Hershman. |
Perhaps even more surprising than Helicoprion’s physical features is its newfound phylogenetic
placement. While commonly referred to as a shark (you don’t know how hard it
was not to refer to it as such in this post; I’ve always known it to be a
shark), Helicoprion is actually more
closely related to ratfish than it is to true sharks. Ratfish are part of the
class Chondrichthyes (cartilaginous fish), but they are not sharks; they are part
of a different subclass. Helicoprion was
found to be part of this separate subclass, very close to the point at which
sharks and ratfish diverged. (Tanapila et
al., 2013)
A brand-new look for Helicoprion, and it only took over 114 years to discover it. Reconstructions by Ray Troll. |
The fact that such a large fish, sometimes reaching 8m
(~25ft) long, was so common and yet only distantly related to true sharks
reveals a lot about the environment in which it lived. With no large marine
reptiles yet ruling the seas, and certainly no whales, all of the major niches
were filled by fish. Helicoprion was
able to grow to great sizes as it filled a niche which, it seems, no other
animals were exploiting: hunting cephalopods and other soft-bodied creatures. (Lebedev,
2009) Helicoprion was unlikely to be
the only specialized holocephalan at this time; the diversity of such fish was
far greater back then. Eventually, such strange fish did go extinct, and in
their wake, sharks and rays evolved to fill their niches.
It is a wonder that over 100 years after its discovery,
we are only now discovering new information about Helicoprion. It has had a confusing, misfortunate, and pretty
hilarious history, but it seems that all the speculations and hypotheses of the
function and position of its characteristic whorl can be put to rest. While not
as outlandish as some depictions, the real Helicoprion
was no less unusual or unique.
References
Lebedev,
O. A. (2009). 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. doi:10.1111/j.1463-6395.2008.00353.x
Tapanila,
L., Pruitt, J., Pradel, A., Wilga, C. D., Ramsay, J. B., Schlader, R., &
Didier, D. A. (2013). Jaws for a spiral-tooth whorl: CT images reveal novel
adaptation and phylogeny in fossil Helicoprion.
Biology Letters, 9(2). doi:10.1098/rsbl.2013.0057
Coverage by Brian Switek at Laelaps: http://phenomena.nationalgeographic.com/2013/02/26/buzzsaw-jaw-helicoprion-was-a-freaky-ratfish/
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