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Leedsichthys, Largest Prehistoric Fish, Now Known To Have Been About 50 Feet Long

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This is one ancient whale of a tale! An international team of scientists from the National Museums Scotland and the Universities of Glasgow and Edinburgh have completed a years-long project to excavate and assemble the most complete fossil of the world's largest prehistoric fish.

The specimen suggests that Leedsichthys problematicus grew to a full size of around 50 feet long, twice that of previous estimates, according to a written statement from the University of Glasgow.

The massive fish must have cast an impressive shadow as it swam through the seas about 165 million years ago. With a bony physique, Leedsichthys pioneered an important ecological niche: It was the first of the giant plankton-feeders, whose modern-day equivalents today include the behemoth whale shark.

Research team leader Dr. Jeff Liston of the National Museums of Scotland told The Huffington Post in an email that several significant conclusions can be drawn from the Leedsichthys discovery.

"Overall, this find indicates a likely significant change in the faunal composition of plankton in the Middle Jurassic seas, to suddenly allow an animal to be this successful, when previous vertebrate suspension-feeders did not exceed 55 centimeters in length," Liston said. "Also, the information that we are gaining about the honeycomb mesh structure that this animal had on its gill rakers, to help extraction of plankton from the water column, gives us some interesting mechanical comparisons with animals like the whale shark, basking shark and the manta ray."

Liston said the specimen's impressive length proves that the increase in size among land dinosaurs -- a phenomenon known as gigantism -- was occurring in a parallel process under the water.

Leedsichthys fossils had frustrated researchers ever since the very first fossil was found by British collector Alfred Leeds in 1889. Since then, bones of the ancient fish have been found from Germany to Chile, but their fragility made for a reconstruction and classification process so difficult that Liston said it inspired the "problematicus" part of the fish's name. It also meant measuring the big fish involved a lot of guesswork.

The most recent specimen, discovered in 2001 protruding from a cliff near Peterborough, England, represents the most complete example of Leedsichthys ever found, Liston noted. Nicknamed "Ariston" by scientists, the discovery included close to 2,400 bones and required 3,100 hours to excavate.

But the labor was worth it, Liston said, because this fossil can now be used to help fill in gaps in the greater fossil record.

"[Ariston acts] as a sort of Rosetta Stone and [ties] together the more fragmentary other specimens that had been excavated over a 115-year period," Liston told HuffPost. "Ariston was the missing piece that linked the other individuals together into a 'whole' that we could really use to look at Leedsichthys close up."

The team's results will be published in "Mesozoic Fishes 5: Global Diversity and Evolution -- Proceedings of the International Meeting," and presented at the 61st Symposium on Vertebrate Palaeontology and Comparative Anatomy in the Royal Society of Edinburgh, National Museums Scotland on Friday.

CORRECTION: The text has been changed to more accurately describe the Leedsichthys' relationship to modern-day plankton-eaters, including the whale shark.

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