Frogs: The Animal Answer Guide

1. Introducing Frogs

What are frogs? Frogs are members of the class Amphibia, often called amphibians, which includes all frogs and toads in addition to two other less-familiar groups of animals. Frogs and toads are vertebrates—animals with backbones —which are generally recognizable and not easily confused with other animals. People rarely, if ever, say, “Is that a frog?” Instead, they are interested in identifying specific frogs or toads. Frogs and toads differ from two other groups of amphibians, salamanders and caecilians, because they lack a tail as an adult. Thus, they are placed in the order Anura, which means “no tail.” Scientists often refer to frogs and toads, collectively, as anurans. In addition to lacking a tail, most frogs and toads have long hind limbs modified for jumping or, at least, hopping. Frogs and toads are well known for their reproductive behavior, which, for most species, includes loudly calling at certain times of the year to attract mates. Listening to frogs calling around a wetland or swamp is a relaxing pastime. Most frogs and toads also lay eggs, and many species, including those most familiar to people, have an aquatic larval stage usually referred to as a tadpole. Frogs are often used as excellent examples of metamorphosis: tadpoles slowly develop legs, lose their tail, and crawl or hop onto land. Although all frogs and toads have the same basic body plan, their varying body forms and other aspects of their biology make frogs and toads an amazingly diverse and significant group of animals. Of the three main groups of amphibians, frogs and toads comprise approximately 90 percent of all known species. In addition, they are the most widespread group of amphibians in terms of Chapter 1 Introducing Frogs 1 2 Frogs: The Animal Answer Guide geographic distribution and, in many regions, represent the only type of amphibian present. What is the difference between frogs and toads? People become confused about the differences between frogs and toads and how to tell one from the other. Scientists consider all frogs and toads to be members of the order Anura, or the “tailless” amphibians, and often refer to them as “anurans.” But the terms frog and toad are not necessarily restricted to specific groups of anurans. In general, frogs are considered to be anurans with relatively smooth skin, long hind legs designed for jumping long distances, and heavily webbed toes for swimming or adhesive toepads for climbing. Frogs often tend to be more aquatic than toads and include familiar species, such as bullfrogs and leopard frogs. Some frogs, especially treefrogs, are much more arboreal (tree-climbing). Toads are usually considered anurans that have relatively short legs designed for hopping shorter distances, little to no webbing between their toes, and limited ability to climb. Their bodies are typically stouter than frogs and have drier skin, often covered with bumps that resemble warts. When amphibian biologists use the term true frogs, they are usually referring to members of the family Ranidae, which includes northern leopard frogs (Rana pipiens), pickerel frogs (Rana palustris), bullfrogs (Rana catesbeiana), or the common frog (Rana temporaria) found in Europe. The term true toads refers to members of the family Bufonidae, which includes Fowler’s toads (Bufo fowleri), the common toad (Bufo bufo) of Europe, and the tiny oak toad (Bufo quercicus). However, Ranidae and Bufonidae are only 2 of more than 30 anuran families , and most anurans are not members of either of these families. Consequently , most scientists who study amphibians refer to the entire group as anurans. Among scientists and laypeople, it is acceptable to refer collectively to all anurans as frogs, reserving toads for less-aquatic anurans with relatively short legs and relatively dry skin. In some parts of the United States, the term toad is applied not only to true toads but also to the spadefoot toads in the family Scaphiopodidae and the narrowmouth toads in the family Microhylidae. What other types of amphibians are there? Although frogs and toads (anurans) represent the most abundant and diverse group of amphibians on earth, two other primary amphibian groups are extremely interesting and, in some parts of the world, represent important components of the ecosystems in which they live. One group of amphibians other than anurans is salamanders. If frogs and toads are the tail- 3 Introducing Frogs less amphibians, then salamanders are tailed amphibians. All salamanders are in the order Caudata, which means...