Canadian-Scottish team identifies prehistoric fish as largest ever to swim Earth’s oceans

Scott Sutherland

A team of researchers from Canada and Scotland has shown that the prehistoric fish known as Leedsichthys problematicus was the largest bony fish to ever swim the oceans, capable of growing over 16 metres in length!

Leedsichthys problematicus was a large plankton-eating fish that existed over 165 million years ago, while dinosaurs roamed the Earth. Researchers have been finding fossils of this species for years, but the remains were always incomplete and difficult to classify (thus earning it its name). Without a full skeleton to measure from end-to-end, though, it was difficult to know the exact size of the species. Guesses were made using the various parts of it, but it wasn't until a new fossil was recently discovered near Peterborough, UK, that researchers were able to figure out how big it can get.

"We sat down and looked at a wide range of specimens, not only at the bones, but their internal growth structures as well — similar to the growth rings in trees — to get some ideas about the ages of these animals, as well as their estimated sizes," said Professor Jeff Liston from the National Museum of Scotland, who led the research team, according to a University of Glasgow statement.

"What we have demonstrated here is that a small adult Leedsichthys of 8-9 metres could reach that length within around 20 years, whereas after 38 years it would be around 16.5 metres long — possibly even outgrowing today's massive whale sharks."

Scientists from the Royal Tyrrell Museum of Paleontology, in Drumheller, Alberta, as well as the University of Edinburgh and the University of Glasgow, worked with Liston to piece this all together. Their research appears in the latest issue of Mesozoic Fishes.

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Finally locking down the size of this massive fish has given the researchers a clear insight into a major change in the Earth's oceans during the Jurassic period. Before fish like Leedsichthys showed up, plankton-eating fish were fairly small by comparison, may reaching half a metre in length. With Leedsichthys able to grow so large, they would need an abundant food source, meaning that there must have been a population explosion of plankton in the oceans at that time.

Liston said: "This has implications for our understanding of biological productivity in modern oceans, and how that productivity has changed over time."

(Image courtesy: Wikipedia)

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