Reptiles and Amphibians

Introduction

"Herps"

The study of amphibians and reptiles is called herpetology and a person who studies them is called a herpetologist. For this reason, amphibians and reptiles together are often called "herp" for short.

Both reptiles and amphibians have spectacular histories. Now extinct species were numerous and widespread, dominant forms of life in their time. Amphibians ruled for 140 million years, reptiles for 130 million years. The herps we know today are a very small fragment of what existed in prehistoric times.

Both groups are misunderstood, perhaps because both reptiles and amphibians include certain venomous species, or perhaps because their habits often seem strange. But herps are just animals like any others. They are not magical. They must eat, drink, sleep, move about, produce young, flee enemies and do all the basic things any animal must do.

Both amphibians and reptiles are cold-blooded, which is a very poor expression that has unfortunately fallen into common use with herps. It really has nothing to do with blood and coldness. What it means is that amphibians and reptiles ontain their heat from the environment. Birds and mammals are warm-blooded, again, a poor expression, but meaning that a bird or mammal generates its own body heat. For people this is 98.6^oF. Most amphibians and reptiles cannot produce heat. Their bodies are usually the same tempature as the surroundings. They are usually active in warm surroundings and sluggish in cool surroundings. After a meal, herps will seek a warm spot to give them the heat they need to digest their food. Many reptiles will sit on a surface exposed to the sun, this form of tempature regulation is called basking. If the spot becomes too hot, they will move away. Extremes of heat or cold will kill them. Most species living in temperate zones hibernate in the winter. Because they obtain heat from their environment, herps cannot survive in very cold regions sich as the Artic. The greatest number of species occurs in the tropical regions of the world.

Amphibians

Ancient amphians were the first animals to attempt life on land, 340 million years ago, and today's amphibians are still amateurs at the business of living out of water. Amphibian skin is moist and easily dried out. It has no protective covering such as scales, feathers or fur. Since drying out would mean death, amphibians must remain in or near water, or in moist locations such as under logs or leaves. Amphibian eggs are soft and jelly-like and like the amphibians themselves, dry out easily. They must be laid in water or at least in a wet, protected location. Even amphibians such as toads and salamanders, which have gotten some degree of independence from water, are forced to return to water to reproduce. Amphibian young show most clearly the dependence of this group on water. The eggs hatch not into small copies of the parents but into creatures that look more like fish. These are larvae, often called tadpoles. Tadpoles have gills with which to breathe in water. When first hatched, they are legless, but legs grow gradually and with other changes, the larvae soon come to look like the parents and can then emerge from the water. This change from larval to adult form is called metamorphosis. The word amphibian comes from a Greek word that means "living a double life".

Amphibians include salamanders and newts, frogs and toads, and a group called caecilians. Caecilians live in the tropics, are shaped like worms and due to their burrowing habits are not often seen.

Salamanders are the amphibians most often confused with reptiles because they have the same general body shape as lizards. However, it is easy to tell them apart, for lizards have scaly skin and claws, while salamanders are smooth-skinned and have no claws. Salamanders differ in their dependence on water. Some live their whole life in water, while others live on moist land and return to water only to mate and lay eggs. Some salamanders which live in water their entire lives are the mudpuppies, the hellbenders, and congo eels, which tend to be rather large (about 12-30 inches long) and the sirens which also tend to be large and lack hind legs. Newts, a water dwelling group without gills, have a land stage called an eft which occurs between the larva and the adult. The common tiger salamander, which live most of its life on land, has an alternate larval form called the axolotl which is able to reproduce without losing its gills and leaving the water. There are also several pale-colored, eyeless cave dwelling salamanders which live their entire lives in darkness. North and Central America together have a generous assortment of the world's salamanders. Frogs and toads are easy to recognize since they lack tails, having tails only as tadpoles. Frogs usually have smooth skin and live in water, while toads have warty skins and live on land, but in some parts of the country the words toad and frog may be used interchangeably. Toads are often adapted to dried conditions. The spadefoot toad is able to breed in temporary pools after rains, for the young develop very quickly. Common toads have poison glands which are irritating to the mouth of any predator. The bullfrog and leopard frog are examples of common true frogs. The little tree frogs, including spring peppers, are a large group, some very tiny and most veery loud-voiced. Many have pads on their toes which allow then to cling to vertical surfaces. In the tropics is a group of so-called "poison-arrow" frogs, which is extremely toxic. They are often brightly colored in oranges, yellows or greens.

Most differences between amphibians and reptiles can be seen as changes making it easier to live on land. Most reptiles are not as dependent upon nearby water as amphibians. Reptiles have solved the drying-out process by having the skin covered with hard, overlapping scales which help to keep moisture from excaping the body. Reptile eggs do not need to be laid in water because, unlike amphibain eggs, they have a tough shell which helps conserve moisture. Some reptiles may even retain eggs inside the body until they hatch, then giving birth to live young. (This is not the same as mammalian live birth.) Young reptiles do not have a larval stage. They look just like their parents, only smaller in body form and their color and markings may be different.

Finally, reptiles have claws on their feet to help climb, run and dig on land. Because most reptiles are not dependent upon a body of water for reproduction, they can live in places such as deserts where it would difficult for amphibians to survive. Some reptiles, such as crocodilians, many turtles, some snakes and a few lizards have gone back to living in the water, but they breathe air through their lungs and must still emerge from the water to lay their eggs on land. Among the larger reptiles are the crocodile family; including alligators, crocodiles, caimans and gavials. These animals are commonly 10 feet or more in length. They are aquatic but come out of the water to bask and build nests for their eggs. They have a general lizard-like shape, but are much bigger and have large-many-toothed jaws. The turtle family is a very old and diverse group, unchanged for millions of years, including huge 1500 pound leatherback sea turtles and giant Galapagos land tortoises thought to be well over 100 years old. Turtles have their skeletons modified into a shell into which many of them can withdraw for protection.

Seagoing turtles are streamlined for swimming and cannot draw their heads into their shell. Their feet are shaped like flippers, which makes their coming onto land to lay eggs a difficult task.

Some freshwater turtles, such as snappers and softshells, seldom come out of water although they are able to walk easily. Many freshwater turtles such as painted turtles and red-eared sliders come out often to bask in the sun. Land turtles, such as box turtles and wood turtles, spend most of their life on land but like to soak in water occasionally. The gopher tortoise is a land dweller which digs complex burrows in the earth. The lizard family is most often confused with salamanders, which are amphibians. Lizards have have scales and claws, while salamanders do not. Most lizards have eyelids, ear openings, four legs and a tail. Lizard tails break easily if seized but can grow back. Some lizards, called glass lizards, are actually legless and resemble snakes. They do have eyelids and ear openings, however, and can be told apart in this manner. The snake family is closely related to the lizards and is considered the most modern group of reptiles. Snakes have no legs at all and have developed a special way of moving by pushing against the ground and nearby surfaces. Some snakes, the boas and pythons, have tiny external claws which are left over from the former hind legs. Snakes have no movable eyelids and no external ear opening. All snakes are carnivores, that is, they eat other animals rather than plants. Prey is always swallowed whole because the snake is not eqipped with legs and claws with which to tear it into bite-size pieces. There are several methods of prey capture, depending largely on the type of prey. Common water snakes and gartersnakes, which eat fish, frogs, worms and such soft animals merely seize and swallow them, because this type of prey can cause little damage to the snake. Rat snakes, corn snakes, boas, pythons and many others which feed on rodents, kill the prey before swallowing it, by winding around it and suffocating it. This construction is necessary because such prey have sharp teeth and claws and could easily injure the limbless snake. Some snakes, such as rattlesnakes and copperheads, have specially developed poison glands. The venom is injected into the prey and the prey is seized after it drops. This provides the snake with a very safe method of capture. Unfortunately, many people believe that all snakes are venomous, which is not true, since most are harmless. The shape of the snake's head has nothing to do with whether the snake is venomous or not. There are more misunderstandings about snakes than about almost any other animal. The best rule is simply not to touch any snake you cannot identify, if you should be in an area where venomous snakes occur.

The final reptile group has only one member. This is a very ancient "living fossil", the tuatara, which looks like a lizard but belongs to a different reptile branch. The tuatara, unchanged for 200 million years, is found in New Zealand and is protected, for is has a very slow rate of reproduction and matures very late in life. More information about this species can be found at the following web sites: WWF's Tuatara page (exit DNR).

Last Revised: May 15, 2006