|A tadpole in our pond at the outdoor classroom.|
Tadpoles and frogs are vertebrates. Vertebrates are any animals that have an internal skeleton with a backbone. That means mammals, birds, reptiles and fish are also vertebrates. Can you think of animals that don't have backbones? (Answer below*.) Any vertebrate that starts its life in the water and undergoes metamorphosis is called an amphibian. The word amphibian makes sense if you know what the parts of it mean: amphi- means both, and -bian means life form. Amphibians include frogs, toads, newts and salamanders.
Why do you think fish are such better swimmers than tadpoles? Compare the body shape of a tadpole to a fish, then try an experiment. First, find a pool and a life guard. Then jump into the swimming pool and swim like normal using your arms and legs to help you. Then hold your arms and legs into your body and try to swim - it's not so easy without appendages, is it? Tadpoles do not have fins like fish do, and fins are great for steering while you're swimming. They have only a tail to help push them along. That's why tadpoles wriggle around so strangely and fish swim with ease.
How do you think the tadpoles got to our pond? Frogs had to have laid the eggs that grew into these tadpoles, but how did the frogs get to our pond? They have to stay near water, and there aren't other ponds nearby. Frogs could not have gotten to our pond to lay eggs! One possible answer could be related to the fact that frog eggs are somewhat sticky. If a bird stood in a different pond and frog eggs stuck to its feet, then the bird came to our pond, it could have brought the eggs that hatched to our tadpoles. That makes frog eggs disperse just like the kinds of seeds that stick to animal fur - which would be animals imitating plants!
*Invertebrates include insects, spiders, clams, snails, sponges, jellyfish, sea stars, and thousands more types of organisms.