Chuck Bednar for redOrbit.com – Your Universe Online
A distinctive 200-million-year-old fish used a combination of jutting front teeth and pebble-shaped rear teeth to feed on bivalves and other hard-shelled creatures it could find from the sea floor, according to new research from the University of Bristol.
The Jurassic Period fish, known as Dapedium, was found in the Lower Lias rocks of the UK’s Dorest coast near the coastal town of around Lyme Regis. It was one of many different groups of fishes to arrive during that time, and was also among several different ancient animals discovered by 19th century fossil collector Mary Anning, according to the university
Dapedium is described as a deep-bodied fish that resembles a dinner plate when looked at from the side. It could grow to more than one-half meter in length, and had a tiny mouth with the two distinct type of teeth that allowed the fish to crunch through hard shells.
The eating techniques used by Dapedium were discovered by Bristol undergraduate student Fiann Smithwick, who adapted a new level-based mechanical model used to study the mechanics of modern fish jaws to reconstruct the ancient creature’s feeding habits. His findings were published online earlier this week in the journal Palaeontology.
During the course of his research, he examined 89 Dapedium speciments from the Natural History Museum, Bristol City Museum, and the Philpot Museum in Lyme Regis. He measured the position and lengths of each of their jaw bones, then calculated the positions and orientations of the jaw muscles. Finally, he varied these to include several different models.
“Every time he ran the model, the result was the same,” said Professor Mike Benton, who supervised the author. “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.”
When compared to modern types of fish, Dapedium was found to be a close match to modern sea breams, another type of fish that is flat-sided and deep-bodied. Sea breams also crush shells in their small mouths using blunt-topped teeth, the university explained.
Dapedium lived alongside many of the great sea reptiles of the Jurassic, including the dolphin-shaped ichthyosaurs, long-necked plesiosaurs, and even some marine crocodilians. The fish was likely able to avoid being captured by these predators because of its thin body, which would have made it difficult to see head-on, and because it stayed close to reefs and seabeds.
Professor Benton said that he and his Bristol colleagues are “delighted to see such an excellent piece of work carried out by an undergraduate,” adding that Smithwick “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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