Jurassic Fish Had Jaw That Could Crush Shells

A fish from the Jurassic period had a jaw so strong that is could crush hard shells, a new study shows.

Known as Dapedium, this fish was one of many marine species that came on the scene 200 million years ago, including ancestors of salmon, cod, seahorses, and perch.

Dapedium was a deep-bodied fish shaped like a dinner plate known from the Lower Lias rocks of the Dorset coast around Lyme Regis. And it may have boasted a tiny mouth with little pebble-shaped teeth, but it apparently had a nasty bite.

"My work indicates that Dapedium was well adapted to crush shells," said researcher Fiann Smithwick, an undergraduate at the University of Bristol, said in a statement, "feeding on bivalves and other hard-shelled creatures that it could scrape from the sea floor."

Smithwick studied 89 specimens of Dapedium using a fish model to get a better sense of the jaw mechanics and feeding behaviors of this remarkable ancient creature.

"Every time he ran the model, the result was the same," explained Professor Mike Benton, Smithwick'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."

Though Dapedium had a shell-crushing jaw, it would be no match for the Jurassic predators swimming alongside it, such as the dolphin-shaped ichthyosaurs, long-necked plesiosaurs, and even some marine crocodilians. The researchers guess that it likely escaped detection because its body was so think that it was hard to see head on.

For comparison, Dapedium most closely resembles the modern day fish called sea breams, which are also flat-sided, deep-bodied, and can crush shells.

The research was published in the journal Palaeontology.

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