Page last updated at 19:12 GMT, Thursday, 18 February 2010

Giant fish swam prehistoric seas

Artist's reconstruction of Leedsichthys (artwork by Robert Nicholls)
Leedsichthys was a giant filter-feeder in prehistoric oceans

Prehistoric seas were filled with giant plankton-eating fish which died out at the same time as the dinosaurs, new fossil evidence suggests.

Scientists from Glasgow, Oxford and the United States have identified fossil evidence which shows the fish existed between 66 and 172 million years ago.

They believe it may be a "missing piece in the evolutionary story of fish, mammals and ocean ecosystems".

The findings of the research are published in the journal, Science.

The international team which carried out the study included academics from Glasgow and Oxford Universities, DePaul University in Chicago, Fort Hays University in Kansas and the University of Kansas.

It was only after these fish vanished from the ecosystem that mammals and cartilaginous fish such as manta rays, basking sharks, whale sharks began to adapt to that ecological role
Dr Jeff Liston
Glasgow University

The project began in Glasgow, with a review of the remains of the giant Jurassic fish Leedsichthys, in conjunction with the excavation of a new specimen of this creature in Peterborough.

Scientists viewed Leedsichthys as an isolated example of a giant filter feeder in the oceans during the age of dinosaurs.

But there was a gap in the fossil record between it and the first appearance of modern filter-feeders, some 100 million years later.

Dr Jeff Liston, from Glasgow University, ran the excavation in Peterborough and found the new specimen to be an anomaly.

"The breakthrough came when we discovered additional fossils, similar to Leedsichthys, but from much younger rocks," he said.

New fossils

"These specimens indicated that there were giant filter-feeding fishes for much longer than we thought.

"We then started to go back to museum collections, and we began finding suspension-feeding fish fossils from all round the world, often unstudied or misidentified."

Several of the most important new fossils - all from the same extinct bony fish family as Leedsichthys - came from sites in Kansas.

Other remains originated as far afield as Dorset and Kent in the UK, and in Japan.

Artist's reconstruction of Bonnerichthys (artwork by Robert Nicholls)
Bonnerichthys was identified from a fossil found in Kansas

Dr Liston added: "The fact that creatures of this kind were missing from the fossil record for over 100 million years seemed peculiar.

"What we have demonstrated here is that a long dynasty of giant bony fish filled this space in time for more than 100 million years.

"It was only after these fish vanished from the ecosystem that mammals and cartilaginous fish such as manta rays, basking sharks, whale sharks began to adapt to that ecological role."

Dr Liston said the findings had "implications for our understanding of biological productivity in modern oceans, and how that productivity has changed over time".

One of the best preserved Kansas specimens had previously been interpreted as similar to a fanged predatory swordfish.

When members of the team began to clean the specimen, they found a toothless gaping mouth, with an extensive network of thin elongate bony plates to extract huge quantities of microscopic plankton.

The team named this four to five metre-long fish Bonnerichthys, in honour of the Kansas family who discovered the fossil.



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