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"Biggest Fish Ever Found" Unearthed in U.K.

James Owen in England
for National Geographic News
October 1, 2003
 
Fish tend to inspire exaggerated tales, as anglers know all too well.
But paleontologists digging up a giant fossilized fish in England have
plenty of bones to back their claim that this really was one heck of a
whopper. First, however, they've got to piece all the evidence together.

Discovered by two paleontology students in clay pits near Peterborough, the fossil is the largest known fish ever recorded. Identified by experts from the universities of Portsmouth and Glasgow, Leedsichthys problematicus swam the world's oceans some 155 million years ago.


"It's by far the biggest and most complete Leedsichthys ever found, which makes it the biggest fish ever found," said Mike Barker, head of paleobiology at Portsmouth University.

Equipped with massive, teeth-lined gills, experts say the creature was probably one the first giant planktivores. A Jurassic version of the baleen whale or basking shark, it would have filtered out huge quantities of tiny shrimp and other marine organisms while cruising over what is now central England.

The Peterborough specimen's estimated length is 22 meters (72 feet)—almost twice as long as a whale shark, the largest fish swimming today. Those working on the fossil reckon the species may have reached sizes to rival the blue whale.

Named after Alfred Leeds, an English farmer who first discovered Leedsichthys problematicus in the late 1800s, "problematicus"reflects difficulties paleontologists had in classifying the species, eventually linking it to an extinct group of bony fishes called pachycormids which had sickle-shaped pectoral fins and forked tails.

Problem Fish

Leedsichthys is proving equally problematical for today's fossil experts. The Peterborough site contains a tangled mass of thousands of fractured bones, making the task of excavation akin to tackling a gargantuan, mud-caked jigsaw puzzle.

"It's far more complicated than digging up a large reptile or a dinosaur," said dig leader Jeff Liston, vertebrate researcher at Glasgow University's Hunterian Museum in Scotland. "Its bones are exceptionally thin, and are crushed by the weight of clay over millions of years. Another problem is that many fish from this family had only limited calcification of their skeleton, so many parts simply do not preserve."

He added: "There's still a stupendous quantity of bones we're trying to get out. The previous biggest specimen, called Big Meg, filled about 20 museum drawers. We've already got almost 120 drawers of material."

In fact, Liston says he felt relieved when his team discovered the fish's tail section was missing, having been quarried out during clay extraction work in the late 1980s. "The last time someone tried to excavate the tail of this animal it came out in just under 10,000 fragments," he said.

Liston and his team estimated the fish's age by examining other fossils and the sediment containing its remains. Tests showed this comprised eight to 10 percent organic material, such as algae and plankton.

This may provide a clue to the sudden extinction of Leedsichthys. Researchers have puzzled over the fact the fish isn't known before the Mid Jurassic period, while no remains have been found later than the early Late Jurassic. One theory is that the fish's evolution was closely linked with a sudden rise in sea levels which engulfed much of Europe. As these plankton-rich seas started to recede, so the fortunes of Leedsichthys also began to ebb.

Extinction Theories

"Nobody's sure quite why it became extinct," said Barker. "But the collapse of the marine ecosystem due to environmental changes must be a leading contender."

Liston puts forward another possibility, linking its demise with the emergence of a brash new breed of bony fishes called teleosts. This group makes up around 95 percent of bony fish living today, including everything from tuna and cod and to halibut and salmon.

Liston believes teleosts would have had a crucial competitive edge over pachycormids due to their reproductive strategy. While Leedsichthys relied on relatively small numbers of well-developed young to perpetuate the species, the newcomers produced huge quantities of small eggs.

"Teleosts start to radiate and diversify at this time," he added. "So imagine a numbers race taking place, where teleosts suddenly become far more successful because there are far more of them, then you can see the pachycormids are going to get edged out."

Once all the remains are removed from the dig site, Liston says it will take many months and even years to piece them back together, with further funding needed to complete the work.

But eventually the world's biggest known fish will be in a fit state to show the public. Provided, of course, they can find somewhere big enough to display it.
 

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