Herpetology (from greek: 'ερπετόν, "creeping animal" and λόγος, logos, "knowledge") is the branch of
zoology concerned with the study of
reptiles and
amphibians. Many biologists use the term "herp" or "herptiles" for all reptiles and amphibians.Herpetology is concerned with poikilothermic, or
cold-blooded, tetrapods. "Herps" include
salamanders,
frogs,
toads,
snakes,
lizards,
turtles,
tuataras,
crocodilians and an odd group of amphibians called
caecilians, but exclude fish. Two classes are categorized within herpetology: reptiles and amphibians. These groups share poikilothermy, and sometimes a superficial resemblance to one another (e.g. salamanders and lizards are often confused) but are not closely related in an evolutionary sense. Amphibians have
permeable skin that allows for the exchange of gases, very much like the tissue that makes up mammalian lungs. Many amphibians do not have lungs at all, but use their skin alone for gas exchange and
respiration. Amphibians have a three-chambered
heart, and are often bound to water for at least part of their lives. Amphibians have glandular skin, and many of them produce toxic secretions in some of their skin glands, warding off predators and generally tasting bad. Reptiles, by contrast, have a dry watertight skin, usually protected by
scales, that normally has few if any glands. Many species of reptiles spend no part of their lives anywhere near water, and they all have lungs. The reptilian heart is three-chambered (four-chambered in the case of crocodilians), and living reptilians usually, if not always, lay eggs or give birth on land, including marine turtles, which only come ashore for this purpose. Again, extinct creatures may have exhibited some differences. A number of reptilian species, most notably some of the snake species,
are born live, not hatching from
externally laid eggs.
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