Jaw mechanics of a shell-crushing Jurassic fish revealed

The feeding habits of an unusual 200-million-year-old fish have been uncovered by a University of Bristol undergraduate in a groundbreaking study which has been published in Palaeontology, a leading scientific journal, this week -- a rare achievement for an undergraduate student.

The Jurassic fish, Dapedium, known from the Lower Lias rocks of the Dorset coast around Lyme Regis, was one of many new groups of fishes that came on the scene 200 million years ago. These included ancestors of the modern teleost fishes -- the group of 30,000 species of salmon, cod, seahorses, and perch -- that dominate the waters today.

This distinctive fish was also one of a number of ancient animals first discovered by the pioneering nineteenth century fossil collector Mary Anning, and fascinated early palaeontologists such as Henry De la Beche and Louis Agassiz.

Dapedium was a deep-bodied fish, shaped like a dinner plate in side view, which could grow to over half a metre in length. It had a tiny mouth with jutting front teeth and masses of pebble-shaped teeth further back.

In his research, Bristol undergraduate Fiann Smithwick applied a new lever-based mechanical model, developed to understand the jaw mechanics of modern fishes, to reconstruct the feeding behaviour of this extraordinary ancient fish.

"My work indicates that Dapedium was well adapted to crush shells," said Fiann, "feeding on bivalves and other hard-shelled creatures that it could scrape from the sea floor."

He examined 89 specimens of Dapedium in the Natural History Museum, Bristol City Museum, and the Philpot Museum in Lyme Regis, and measured the positions and lengths of the jaw bones. He calculated the positions and orientations of jaw muscles and varied these to include all possible models.

"Every time he ran the model, the result was the same," explained Professor Mike Benton, Fiann's supervisor. "The outputs showed that Dapedium was a shell crusher. Its jaws moved slowly, but strongly, and so it could work on the hard shells of its prey. Other fishes have fast-moving, but weaker jaws, and those are adapted for feeding on speedy, slippery fish prey."

In comparisons with modern fishes, Dapedium matches closely the modern sea breams. These fishes are also flat-sided and deep-bodied, and they crush shells in their small mouths, armed with blunt-topped teeth.

Dapedium lived side-by-side with the great sea reptiles of the Jurassic, such as the dolphin-shaped ichthyosaurs, long-necked plesiosaurs, and even some marine crocodilians. Dapedium probably escaped being caught by these reptiles because it was so thin-bodied it might be hard to see head-on, and it probably lurked close to reefs and the seabed.

"We are delighted to see such an excellent piece of work carried out by an undergraduate," said Professor Benton. "Fiann was funded by a Summer Research Bursary from the Palaeontological Association, and he devised the project himself, learned the numerical techniques, and wrote it up himself. It's rare for an undergraduate to be able to do all this and pass the scrutiny of one of the world's leading scientific journals."

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The Jaws effect: Biting review finds shark policy based on movie myths

The film Jaws has heavily influenced Western Australia's stance on sharks, a review of over a decade of state government policy has found.

Dr Christopher Neff of the University of Sydney has examined the narratives and shark hunt policies implemented by different WA Governments between 2000 and 2014 and found striking similarities to the 1975 Spielberg classic.

"In particular, the Western Australian Government's current 'Imminent Threat' policy to catch and kill 'rogue' sharks is predicated on Hollywood fiction," says Dr Neff, a lecturer in public policy at the University's Department of Government and International Relations.

In October this year, the West Australian government withdrew an application to the federal government to extend its drumline policy, albeit securing permission to kill sharks deemed by the government to pose 'imminent threat' to beachgoers.

"This policy is using myths as the basis for killing sharks that are protected by law and which provides no real beach safety," he says.

"This fiction serves an important political purpose because films allow politicians to rely on familiar narratives following shark bites to blame individual sharks in order to make the events governable and to trump evidence-based science."

"The message from this research is that politicians do not have a right to their own set of scientific facts about sharks, no matter how popular the movie."

Dr Neff's research, which has been published online in the Australian Journal of Political Science, spells out the 'Jaws Effect' as a political device based on three themes from the film: the intentionality of sharks, the perception that all human-shark interactions are fatal and the idea that killing 'the shark' is the only solution.

"Unpacking the politics of shark bites, or any public policy issue, involves addressing the way words and images are used to paint a picture for the public and inform policy choices. This research therefore offers broader implications for policy analysis," says Dr Neff.

"[It] identifies a worrying style of policymaking where widely known fiction can be used to navigate the attribution of blame and to prescribe policy responses," he says.

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