Published online 18 February 2010 | Nature | doi:10.1038/news.2010.80

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Ancient filter feeders found lurking in museums

Fish fossils fill gaps in dinosaur-era ocean food chains.

BonnerichthysArtist's reconstruction of the 70-million-year old giant suspension-feeding bony fish Bonnerichthys.Robert Nicholls, www.paleocreations.com

The first large filter feeders swam in the oceans for much longer than previously thought.

In a study published today in Science, Matt Friedman, a palaeobiologist at the University of Oxford, UK, and his colleagues identify filter feeders in fossils spanning more than 100 million years and originating in Asia, Europe and North America. The discovery is a result of examining fossils from museums around the world that had either not been studied or had been misinterpreted1.

"Given how widespread they were and how long they appear in the geological records, I think it's an important finding that's really going to force us to think about what role these bony fish had," said Nick Pyenson, a fossil marine vertebrate expert at the Smithsonian Institution's National Museum of Natural History in Washington DC.

Palaeobiologists had thought that large-bodied filter feeders only lived for about 20 million years of the Mesozoic era, but this study demonstrates that they existed from 170 million years ago to 65 million years ago. The newly classified fish plug a gap in the understanding of food webs in the Mesozoic era, which ran from 251 million years ago to 65 million years ago. The absence of those large feeders for most of the era, despite the presence of plankton, had perplexed scientists, in part because of the diversity of modern filter feeders, which include whales and sharks.

Big mouth strikes again

Friedman's study of ancient filter feeders began when he was asked to examine an odd fish fossil from the Rocky Mountain Dinosaur Resource Center in Colorado. It had fins similar to those of ancient predatory fishes but lacked the expected teeth. The fossil's thin skull and long, slender jaw bones reminded Friedman of filter feeders.

"All of a sudden the penny dropped and I realized that this animal was very similar to poorly known animals, ones that were considered unsuccessful from much earlier in the geological record. And here we had a very geologically young example of this group of animals, which dictated that they were around about five times longer than we thought they were before," said Friedman.

Armed with his new knowledge, Friedman searched for other filter feeders in fossils from other museums including the Sternberg Museum in Hays, Kansas and the University of Nebraska State Museum in Lincoln. He found new examples and even corrected some misclassified samples.

forefins of BonnerichthysThe enormous forefins of Bonnerichthys.M. Friedman, University of Oxford.

Palaeontologists frequently have to classify fossil remains based on partial skeletons. Fish fossils often consist mostly of fins and few or no skull bones, and without a head, it is not easy to tell whether the fins belong to a fish that filter feeds or to a fish that hunts. So nineteenth-century scientists often used similarities between fins to group fossils, and some filter feeder bones were classified as the poorly understood kin of toothy predators.

Friedman and his colleagues found other fossils with telltale traits of sieve-faced feeders: long, slender, toothless jaws, a large gill skeleton, and gill rakers, which are elaborate structures that direct water into the gullet. They then created a family tree and found that the newly identified animals were relatively close kin.

"I'm sure that a lot of the collections around the world contain strange bones and nobody knows what they are, and actually they belong to this group," says Lionel Cavin, curator of the geology and palaeontology department at the Natural History Museum of Geneva in Switzerland.

So although the new evidence expands the range of planktivorous vertebrates, it seems as if the hunt for more of them has just begun. 

  • References

    1. Freidman, M. et al. Science 327, 990-993 (2010). | Article | ChemPort |
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