Shark fossil hunt sheds new light into vertebrate evolution

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Washington, January 2 (ANI): A paleontologist has launched a hunt for the fossils of sharks for insights into vertebrate evolution.

Michael Coates, the paleontologist from Chicago, scours sediments hundreds of millions of years old for the deepest branches of vertebrate evolution in the tree of life's shadowy recesses.

These branches determined the basic body plan of jawed vertebrates, including humans and all other four-limbed creatures, when they sprouted more than 300 million years ago.

Coates has now launched a new project on the evolutionary origins of sharks with stimulus funds from the National Science Foundation.

Sharks have drawn attention lately because of their vulnerability to over-fishing and for the ancient genetic underpinnings of their remarkably robust immune systems.

"The question is, what is primitive about living sharks?" said Coates, a Professor in Organismal Biology and Anatomy.

Marine biologists assume that modern sharks are primitive, but modern sharks look somewhat different from their strangely formed ancient ancestors.

A shark called Akmonistion, for example, swam the oceans 320 million years ago, sporting a dorsal fin that resembled a tooth-studded ironing board.

"Sharks are charismatic and they get a lot of media attention, but we've got a very biased view of their abundance and diversity," Coates said.

There are approximately 50,000 species of jawed vertebrates, such as humans and bony fishes, living today.

But, there are only 1,200 species of cartilaginous fish, including sharks, rays and ratfish.

"When you break down the numbers, there are about 400 species of shark that resemble the conventional idea of a shark, but 800 species of batoids-skates and rays. That's where their diversity, such as it is, is locked up," said Coates.

The new shark project fits into the larger scheme of Coates' efforts to marry the fossil and molecule data of early vertebrate evolution.

Major branching events in vertebrate evolution occurred long ago. Sharks branched off the human lineage at least 430 million years ago.

The ray-finned fishes, technically known as Actinopterygians, branched off 420 million years ago.

"Teleosts, the largest subgroup of Actinopterygians, include the vast majority of fishes today," Coates said.

Acanthostega looked like "a large, grotesque salamander," Coates said.

It had legs and digits, with rudimentary ankles and wrists, but also internal gills and a large tail fin.

Acanthostega, along with new work by Coates and Clack on other previously discovered early tetrapods, contradicted long-held paleontological beliefs that early tetrapods all had five digits on each limb.

But, Acanthostega had eight, while other creatures of the same period had seven and six digits. (ANI)

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