ReefQuest Expeditions:

Explorations in
Shark Evolution

text and illustrations by Rick Martin   

 

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Evolution of a Super Predator

Fathoming Geologic Time

Geologic Time Chart

Earliest Sharks

Ancient Sharks

Jaws, Then and Now

Feeding Habits of Cladoselache

Golden Age of Sharks

Helicoprion: an Intriguing Puzzle

Origin of Modern Sharks

Rise of Modern Sharks

Evolution of Lamnoid Sharks

Cretoxyrhina mantelli

Squalicorax

White Shark Carcharodon carcharias

Molecular Clocks and Shark Evolution

Megalodon

Origin of Megalodon

Carcharodon vs Carcharocles

Reconstructing Megalodon

Megalodon Compared with Other Giants

Glossopetrae and the Birth of Paleontology

The Awful Tooth

More than One Way to Size a Fish

Megalodon as a Big Sandtiger

Paleoecology of Megalodon and the White Shark

Trophic Treasure Trove

Extinction of Megalodon

Does Megalodon Still Live?

Ancient, not Primitive

Guide to Fossil and Modern Shark Teeth

Special Thanks

Helicoprion:  an Intriguing Puzzle

They came from mid-Permian deposits in Russia, North America, Japan, and Australia. Curious spiral structures, some 10 inches (26 centimetres) across - or about the size of a large dinner plate. At first, they were thought to be the coiled shell of a somewhat odd ammonite (primitive cephalopods with a spiraling external shell). On closer inspection, it was discovered that they were a continuous whorl of teeth or perhaps dermal denticles from some kind of shark. In short order, the creature was named Helicoprion and the game of trying to figure out how this structure might have fit onto a shark began in earnest. A Russian paleontologist named Andrzej P. Karpinski invested years of his life in futile attempts to restore the position of the whorl. Karpinski tried just about everything. He perched the whorl on top of the first dorsal fin, like some kind of bizarre windmill. He tried hanging it from the tip of the tail, coiled like a piglet's tail. He even placed the whorl on the tip of its nose, making the fish resemble a sinister swimming elephant.

It is now generally agreed that the structure is indeed a complex whorl composed of up to 180 teeth and must therefore have fit somehow into the mouth. Further specimens revealed that the teeth of Helicoprion most closely resembled those of a group of Paleozoic sharks known as edestoids. One of the best-known species, Edestus giganteus, was a 20-foot (6-metre) super-predator (about the same size of the modern white shark) with teeth that kept growing beyond the tip of its snout - looking for all the world like a fish with toothy pinking shears mounted on its nose. The most likely orientation - based on the teeth of Edestus and related edestoid sharks - is that the teeth overhang from the lower jaw like the vertical blade of a circular saw, having coiled about themselves as new teeth were generated from behind. Perhaps Helicoprion used this buzz-saw arrangement to snag squid-like creatures with a sideways swipe of the head while swimming through a school of the soft-bodied molluscs. In any case, Helicoprion exemplifies some of the difficulties involved in reconstructing ancient creatures from only a few clues.

The spectacular Scissor-Tooth Shark (Edestus giganteus), of the late Carboniferous, sported some of the weirdest dentition ever evolved.  Like modern sharks, Edestus continually grew replacement teeth inside the jaws, but unlike them retained old, worn teeth until they protruded far in front of the fish’s head (thus the youngest teeth are at the rear of the jaws, while the oldest are at the tips).  It is not known how Edestus actually used its pinking-shear jaws, but — as it grew to about the same length as the modern White Shark — it must have been a formidable predator indeed.

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