AMPHIBIANS IN GENERAL
best-known amphibians are frogs, toads, and salamanders. Compared to the classes of other
higher animals -- animals with backbones -- amphibians are very primitive
According to the fossil record, here is approximately when the major groups of land animals appeared:
Life originated in the seas. The first animals were simple ones without backbones -- "invertebrate" animals such as segmented worms, sponges, and corals. The first fish were so simple that they didn't even have jawbones for opening and closing their mouths. The first land animals with backbones were the amphibians. The oldest amphibian fossils look like fish with thick, muscular fins. That's because amphibians arose from early fish. The first amphibians lived more in water than on dry land.
Keeping the above points in mind, we can say that, from an evolutionary viewpoint, amphibians as a class developed before many of nature's most useful animal "inventions" had appeared. For instance, look at what amphibians don't have (and this includes today's amphibians):
WHAT THEY CAN'T DO
THE WATER PROBLEM
In most backyards, toads are the most likely of all amphibians to appear. That's because toads have a special adaptation that helps them range farther from water than other amphibians: Their thick, warty skin keeps water inside the toads better than other amphibian skins.
Because water and air so easily flows into and out of amphibian skin, amphibians are much more vulnerable to pollution in water and air than other higher animals. In fact, today amphibian numbers are collapsing all over the world. Acid rain is thought to be responsible for amphibians disappearing from streams, lakes and ponds where they were common only a few years ago. Nowadays we often hear of two-headed or five-legged frogs. Apparently this high frequency of deformity results from pollutants interfering with natural development at the genetic level. Of course, as pollution levels increase, eventually other kinds of animals, even humans, are sure to suffer similar fates...
You can review some amphibian-oriented books available at Amazon.com in both the US and the UK by clicking here.
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Conrad, Jim. Last updated . Page title: . Retrieved from The Backyard Nature Website at .