The ferocious bites of a tiger or crocodile haunt our imagination.

But the biting ability is an adaptation to life on land.

The question is: when did biting evolve?

A new study shows that ancient fish could have evolved in ancient bony fish.

Bony fish predominantly catch their prey by suction, easy to see if you watch the fish in an aquarium when they are offered living small crustaceans or worms to eat: you can see how they are constantly puckering their mouth.

Of course, most sharks do bite, but sharks' evolution has nothing to do with the land vertebrates. On land, vertebrates can't suction and instead they developed biting: the jaws are clamped together to grasp the food item.

Some aquatic vertebrates evolved from land vertebrates and can employ suction, like the mata mata turtle (Chelus fimbriatus) from South America or clawed frogs (Pipidae family) from Africa and South America.

Transition from suction to biting is another adaptation required for life on the ground, explaining more about the transition from fish to land vertebrates.

That's why Molly Markey and Charles Marshall, both from the Museum of Comparative Zoology at Harvard University, investigated fossil skulls from an extinct mostly terrestrial amphibian (Phonerpeton), an earlier extinct mostly aquatic amphibian (Acanthostega), an ancient fish on the line that led to the amphibians, Eusthenopteron, and a living bonny fish, Polypterus (from Africa), regarded as a living fossil and an ancestral type.

They focused on the sutures between skull bones at the skulls' roofs. They are lined with stretchy collagen, and the bony plates slightly slide relative to one another when an organism is feeding.

Polypterus feeds by suction, thus its skull sutures offer a pattern for a suction-organism's skull. "A biting or chewing motion would result in a faint pushing together of the frontal bones in the skull, while a sucking motion would pull those bones ever so slightly apart," said Markey.

The pattern on Eusthenopteron, a 380 million years old species of lobe-finned fish (this group gave birth to the amphibians) was similar to the suction feeders.

But the Acanthostega skull, even if with many fish traits, appeared more similar to a biter than a to sucker. "Even though they spent a lot of time in the water, [the earliest amphibian ancestors] were biting on their prey, which is a prerequisite to capturing prey on land. This is interesting, because it suggests early amphibians inherited their biting jaws from ancestors who lived solely in the water", said Markey.

An old evolutionary puzzle is whether or not fish evolved to land mammals to escape predators or drought or to take advantage of new food sources. "Our findings do support the idea that they came on land to exploit new food sources," Markey said.