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World's Oldest Shark Fossil Found

Sean Markey
National Geographic News
October 1, 2003
 
Add another name to the tide of Canadian rock stars.

Paleontologists announced today they've unearthed the world's oldest, intact shark fossil—a 409-million-year-old specimen of a small, primitive species known as Doliodus problematicus—from a site in New Brunswick, Canada.

The fossil, which measures 23 centimeters (9 inches) long from its snout to upper trunk, includes the fish's braincase, scales, calcified cartilage, large fin spines, and a battery of scissor-like teeth preserved in the upper and lower jaw. Researchers estimate the species only grew 50 to 75 centimeters (20 to 30 inches) long, about the size of a large lake trout.


Randall Miller, a paleontologist at the New Brunswick Museum in Saint John, led the field expedition that found the fossil. He said he hoped merely to collect a few more teeth of Doliodus, a species known to science for over a century. Only later did he learn that his team found the first complete specimen of the ancient shark—and the world's oldest intact shark fossil.

Miller collaborated with Richard Cloutier, a paleontologist at the University of Quebec at Rimouski, and Susan Turner, a world expert on fossil shark teeth at the Queensland Museum in Australia, to describe the fossil. Their paper appears tomorrow in the science journal Nature.

The New Brunswick fossil predates other fossil sharks from Antarctica and South Africa, previously known as the world's oldest, by 15 million years.

Oldest Sharks

Paleontologists say the fossil will help shed light on the early evolution of primitive sharks and other vertebrate, or backboned, fish from the Devonian Period, the era between 418 million and 360 million years ago often referred to as the age of fish when most life on Earth was confined to the world's oceans.

"Quite a few paleontologists or ichtyologists [fish biologists] have been trying to imagine what the oldest shark looked like. … This [fossil] is giving us the information," said Cloutier.

Miller and Turner speculate the shark may have resembled an angel shark, a ray-like bottom-dweller found in most temperate and tropical oceans.

Intact fossils of sharks, a boneless fish, are exceptionally rare. Many ancient shark species are known only by fossil teeth or skin scales. Until the recent find, Doliodus problematicus (Latin for "a problematic deceiver"), was among them.

Researchers discovered the articulated New Brunswick fossil in situ, meaning all its parts, such as the braincase, jaws, teeth, and pectoral fins were found attached in their correct anatomical position. The find will help paleontologists make sense of other isolated, smaller ancient fossil shark specimens.

"I think it's an important discovery, one that raises and answers questions about ancient sharks," said Robert Purdy, a collection curator and paleontologist who studies early sharks at the Smithsonian Institution's National Museum of Natural History in Washington, D.C.

One of the fossil's most intriguing aspects is the large, paired spines on the shark's pectoral fins, the side fins used for steering. The feature was previously unknown in sharks and other chondrichthyans, an order of fish whose modern descendants include sharks, skates, rays, and chimaeras.

Their presence suggests the feature appeared in a common ancestor of jawed vertebrates, or gnathostomes. They also muddy the taxonomy of acanthodians, another, less-understood fish order that has bedeviled the classification of Doliodus problematicus since the shark species was first described in 1892 by English paleontologist A. H. Woodward. (Woodward based his study on a single tooth collected at the same fossil site near Atholville, New Brunswick.)

Teeth found in the shark's upper and lower jaw were also "quiet exceptional," Cloutier said. Clustered three to four deep and arrayed in multiple shapes, the batteries resembled the whorls of self-replacing teeth found in modern sharks. Scientists were unaware that Devonian fish displayed such tooth-replacement adaptations.

The Age of Fish

Four hundred million years ago, the area we know today as the Canadian Maritimes lay south of the Equator on the edge of Euramerica, one of two large continents on Earth that would later separate to become North America and Europe.

Terrestrial animal life was limited to unwinged insects like millipedes and scorpions. There were no trees, flowers, reptiles, birds, or mammals. Vertebrates wouldn't crawl on land for another 90 million years. Most living organisms were found in the oceans, an almost phantasmagoric world filled with primitive species even more diverse than today's marine life.

Atholville, New Brunswick, lay underwater in a coastal estuary, a brackish fresh and salt water environment teeming with life. It was there that the Doliodus problematicus shark perished and was quickly buried in fine sediment, enabling fossilization to occur.

The specimen remained undisturbed until 1997, when Miller led a field expedition to the site. Student assistant Jeff McGovern discovered the shark embedded in an outcrop of a mudstone cliff.

Two months later, Cloutier, the Quebec paleontologist, found the counterpart to the shark's braincase lying exposed on the outcrop while on a fossil hunting trip for Devonian plants.

Only later, while comparing specimens, did Miller and Turner realize that the fossil specimen came not only from the same ancient shark species, but from the same individual.

Researchers say their next steps are to more fully describe the fossil and to analyze the shark's compressed braincase under a CAT scan at a laboratory at the University of Texas in Austin that specializes in imaging paleo-objects.

Miller said he also hopes to study the relationship, if any, between Doliodus problematicus and giant, ancient sea scorpions, a type of eurypterid related to horseshoe crabs. A contemporary of Doliodus, the creature grew up to two meters long (6.5 feet) and bore a vague resemblance to a scorpion or lobster.

"Imagine a lobster standing on its tail that's as tall as you are," he said.

And you thought sharks were scary.
 

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