You probably know that frogs hop (双足跳). But did you know that there's a small frog in the Pacific Northwest that belly flops (肚子先着水)? It's called a tailed frog.
Dr. Rick Eisner, who has been studying tailed frogs for the past few years, says, "I've looked at thousands of jumps and have never seen them land on their feet like other frogs." Most of the time, tailed frogs land on their stomachs and then bring their back legs in to prepare for another jump.
Eisner first noticed these frogs because of the way they swim. Other frogs kick both of their back legs at the same time. But when a tailed frog swims, it pushes first with one leg and then the other.
To try to find out why tailed frogs bellyflop, Eisner and other scientists collected and filmed different kinds of frogs. They found that all of the frogs start their jumps the same way: They hold out their legs. The change comes in the landing. Tailed frogs can't move their back legs as quickly as other frogs do. Maybe they don't need to. Tailed frogs live around water and quickly jump into the water to escape danger.
Early frogs developed around watery areas and could jump quickly into the water to escape danger. Scientists think those frogs blended in with (与…融合在一起) the green plants on the side of the rocky rivers, just like today's tailed frogs. "I would guess that other animals would have problems detecting them," explains Eisner. When other animals find those early frogs, the frogs could jump into the river. They didn't need to continue hopping.
Tailed frogs and other kinds of frogs went their own ways about 200 million years ago. Tailed frogs stayed by rivers. Other kinds of frogs moved to places where new hopping skills allowed them to survive.
