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 Scientists on Wednesday announced the discovery of the impeccably
preserved fossilized remains of a shark that lived 325 million years
ago in what is now Arkansas, complete with a series of cartilage
arches that supported its gills and jaws.
Because shark skeletons are made of soft cartilage, not hard bone,
finding anything more than scrappy fossilized remains of teeth and
vertebrae is rare. Finding a fossil shark in an almost
three-dimensional state of preservation, boasting important skeletal
structures, is exceptional.
This primitive shark, named Ozarcus mapesae, may lead scientists to
rethink shark evolution, erasing the notion that these beasts of the
deep have remained little changed since they first appeared at least
420 million years ago.
"These things have been very successful, among the top predators in
the Earth's oceans, for over 400 million years," said paleontologist
John Maisey of the American Museum of Natural History in New York,
one of the researchers.
"The best analogy I can come up with is this: It's like comparing a
Model T Ford with a modern automobile. They are both recognizably
the same kind of thing. But they are completely different under the
hood. We found the Model T of sharks," added Maisey, whose research
was published in the journal Nature.
Those cartilage arches, for example, are quite different from those
in modern sharks, the scientists said. This suggests that while
their general outward appearance has stayed roughly the same,
important changes have occurred over time that have helped make
sharks the perfect eating machines of the sea.
Maisey said Ozarcus mapesae was small by shark standards — about 2
to 3 feet long, with relatively big eyes. It swam in the murky
waters of a shallow inland sea teeming with life including other
fish and squid-like creatures in shells.
It is not the oldest shark fossil, but it is the oldest to reveal
all of the anatomy of the skeleton supporting the gill arches, a
vitally important element of a fish. SOPHISTICATED EQUIPMENT
Employing sophisticated equipment at the European Synchrotron in
France, the scientists used high-resolution X-rays to obtain a
detailed view of the shape and organization of the arches and
associated structures.
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They found that the arrangement was unlike that of modern sharks but
was very much like that of bony fishes like today's tuna or
swordfish. Maisey said that scientists had viewed today's sharks as
very primitive creatures while seeing bony fish as more advanced.
"Modern sharks cannot be considered anymore as living fossils that
did not evolve since their origin. They are actually very derived
compared to early cartilaginous fishes," said American Museum of
Natural History paleontologist Alan Pradel, another of the
researchers.
Sharks have undergone many other changes since the time of Ozarcus
mapesae, the researchers said.
Their jaws are no longer firmly bound to the cranium, giving them
greater biting freedom. Specializations in their inner ear enable
them to hear very low frequency sounds, improving their hunting
ability. They are better at replacing teeth. And there have been
changes in their scales, among other things.
"There's lots of ways in which modern sharks are quite highly
evolved and different from the Model T," Maisey said.
The shark's genus name, Ozarcus, comes from the Ozark Mountain
region where it was found. Its species name, mapesae, honors Ohio
University scientist Gene Mapes, who found it.
(Reporting by Will Dunham; editing by Jonathan Oatis)
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