Extendable Jaws Gave Fish an Evolutionary Edge

Taking your mouth to your plate might not be accepted practice at the human dinner table, but in the fish world it is a winner.

The ability, known as protrusion, allows fish to extend their jaw and snap up otherwise elusive prey, making them effective hunters.

Now an Australian study has tracked the evolution of this trait and suggests it may have been the catalyst for evolutionary change among other marine animals.

Professor David Bellwood, of James Cook University, said protrusion was one of the key traits that made fish efficient hunters with some fish today able to extend their jaws by up to 20 per cent of their body length.

"When we eat a meal we've got to use our hands and forks to bring the food up and push it into our mouth," Professor Bellwood said.

"What the fish can do is take their mouth and put it on to the food.

"It's a huge advantage if you are trying to feed on something that is elusive and fast moving if you are chasing something on the bottom and you've got to get your whole body on to it, then it's like smashing on to a wall.

"We take it for granted that all fishes can snap up elusive prey, but it wasn't like that millions of years ago."

Professor Bellwood, from the Australian Research Council Centre of Excellence for Coral Reef Studies, and his colleagues examined 73 fish from 60 modern species.

The team found the length of a bone in the fish's head - known as the premaxilla - determined its ability to stick its jaws and teeth out.

"There is a strong relationship between the size of that bone and the amount of protrusion," Professor Bellwood said.

"The longer the bone the more protrusion you can do."

The researchers used this marker to then track the evolution of the trait in the fossil record.

"The skeleton of a fish is a little bit like the Rosetta stone of history," Professor Bellwood said.

"If you can read the language of fishes' bones you can then understand their abilities."

He said the trait first appeared around 140 million years, with the appearance of a new group of fish known as acanthomorphs.

However he said the best examples were most evident in fossils around 100 million years old.

"So when the dinosaurs were running around on land, fishes were beginning to play at sticking their lips out," Professor Bellwood said.

Since that time there has been a five-fold increase in the average and maximum jaw protrusion in fish, the researchers report in the journal Current Biology.

Professor Bellwood said this was driven by the increase in acanthomorphs, known as spiny-rayed fish, which are today make up more than one-third of all fish species.

He said protrusion helped acanthomorphs succeed in the evolution arms race.

"They've got this really neat innovation called protrusion and it probably gave them an advantage over a lot of other groups," he said.

Read more at Discovery News