3. Reproduction and life history

‘Reproduction and life history’ discusses the life cycle of amphibians, which includes a fully aquatic, juvenile stage. This is the larva, known in the anurans as the tadpole. It feeds and grows, and eventually undergoes a rapid transformation, or metamorphosis, into the adult. Metamorphosis can take place in as little as nine days from the eggs hatching. A small number of species in all three amphibian orders have evolved the most complete mode of parental care of all, viviparity, which is bearing the young live. An area of interest here is the courtship and mating practices of amphibians.

5. How amphibians feed

‘How amphibians feed’ studies how amphibians feed. Adult amphibians are all carnivores, mostly eating invertebrates. The most effective way for an amphibian to feed when it is under water is to get as close to its prey as possible, then open its mouth suddenly and widely to suck the food in with a stream of water. However, this kind of suction feeding is no use on land. Amphibians feeding on land must use an alternative method. The most common is to have a sticky tongue that can be protruded from the mouth to capture the prey. Another alternative method is to have strong jaws that can grasp the prey directly.

7. Amphibians and humans

‘Amphibians and humans’ looks at the relationship between amphibians and humans. As well as creating myths and folklore about amphibians, humans have always made use of them, as they have so many other organisms with which they share their world. Between three and four billion frogs a year are eaten worldwide. Amphibians also contribute a good number of folk remedies for treatment of disease and injury. In addition, amphibians are harvested from the wild for the pet trade. Humans have also used amphibians in biology teaching and research.

4. How amphibians move

‘How amphibians move’ examines how amphibians move. The three kinds of living amphibians share the same basic biology and life history. However, the anatomy of the skeleton and muscles is very different amongst them. This reflects the different ways that the locomotion of the three respective ancestors evolved. The urodeles retained the most primitive way, with a long body and tail. Salamanders and newts use lateral undulation when swimming, but they also coupled it with limbs for walking on land. The anurans became far more modified by shortening the body, losing the tail altogether, and elongating the back legs. Meanwhile, the caecilians evolved a limbless burrowing mode.

2. The evolution of amphibians

‘The evolution of amphibians’ traces the evolutionary origin of living amphibians: anurans, urodeles, and caecilians. The comparison of the DNA sequence of their genes shows that the living amphibians taken together are a monophyletic group. This means that they all go back to a single common ancestor that had already separated from the common ancestor of the amniotes in the evolutionary tree. However, molecular evidence is little help in discovering which of the ancient tetrapod groups are related to the modern groups. Moreover, the earliest fossils of the three modern groups do not occur until far later, tens of millions years later, than any plausible relatives amongst the Carboniferous and Permian tetrapods.

6. The amphibians’ world

‘The amphibians’ world’ focuses on the amphibians’ sense organs. Amphibians have the eyes, ears, olfactory organs of smell in the nose, and touch receptors common to all vertebrates, but the relative importance of the different senses varies from group to group depending on habitats and modes of life. Anurans have a sensory world most like that of humans; their vision is good, and includes the ability to see colours, and their hearing is acute. Urodeles and caecilians rely much more on their senses of smell and touch. Amphibian larvae have an additional sensory system called the lateral line system. Amphibians use several sensory cues in combination to navigate around their territories.

8. Conservation and the future of amphibians

‘Conservation and the future of amphibians’ reflects on the future of amphibians. Amphibians are small, permeable-skinned animals dependent on a humid atmosphere, which makes them especially vulnerable to changes in habitat and climate. They are also sensitive to increasing pollution levels, although there is a great deal of variation in how badly different species are affected. In addition, amphibians continue to be a source of food, medicine, and pets for the rapidly growing human population, and it is no wonder that as a group they face a particularly severe threat. Many species are endangered or threatened with extinction.

1. What is an amphibian?

‘What is an amphibian?’ provides an overview of amphibians, which zoologists divide into three very unequal sized Orders. The great majority are the frogs and toads, which make up the order Anura, a name that refers to the lack of a tail. The second amphibian order are the salamanders and newts, called the Urodela. Meanwhile, the third amphibian order, the Caecilia, are best known for being poorly known, thanks to their remote distribution and obscure habitat. There are four methods that amphibians can use to breathe: cutaneous respiration, bucco-pharyngeal respiration, pulmonary respiration, and branchial respiration.