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Amphibians and reptiles are also vertebrates: they have a backbone. The joints in between the individual vertebrae allow the backbone to be somewhat flexible.
All reptiles and amphibians, except crocodilians, have three-chambered hearts. The crocodilians need more efficient four-chambered hearts like ours, because of their size.
What comes to mind when you think of reptiles? An alligator poking its head out of a bayou? A snake sliding through the grass? A pet turtle? There's a lot of variety in the reptile world; in addition to the ones just named, there are tortoises; lizards (including Komodo dragons, iguanas, geckos, and skinks); gharials, caimans, and crocodiles; amphisbaenians or 'worm lizards'; and iguana-like tuataras.
Lizards are the largest group of reptiles, with about 4500 species. Geckos are lizards with tiny pads on their feet that help them cling to walls. They eat spiders and mosquitoes, making them helpful critters to have in your house if you live in a tropical climate! Some species make a clicking or squeaking noise that sounds like their name, 'gecko.' Chameleons, another kind of lizard, are most well-known for their ability to change color to blend into their environment. They have protruding eyes that move in different directions at once, so they can see up, down, and to the right and left at the same time!
Snakes are in the same order as lizards, Squamata, but they are limbless and have double-hinged jaws designed for swallowing food whole. Although there aren't as many species of snakes as lizards, they are more widespread.
There are only two living species of tuatara, although at one time there were many more that are now extinct. This animal lives on islands near New Zealand. It has a third 'eye' on the top of its head, thought to be a group of light-sensitive cells which help the tuatara know when it's had enough sun.
Turtles and tortoises (the general term for land-dwelling turtles) have hard shells, usually made out of bony plates covered with keratin - the same substance that forms your fingernails and hair. The top part of a turtle's shell is the carapace; the flat underneath part is the plastron. Leatherback sea turtles and softshell turtles don't have a hard bony plate, but instead have a rubbery skin. Sea turtles spend all of their adult lives in the water - although they still have to surface to get air - except when the females come to land to lay their eggs. Scientists believe they return to the same beach they hatched at themselves. Leatherbacks are the largest turtles, growing up to six feet and weighing 1000 pounds! They are unusual among cold-blooded reptiles in their ability to survive in frigid ocean water.
Giant tortoises live on the Seychelles islands off the east coast of Africa and on the Galapagos Islands, which were named after the Spanish word for tortoise. These huge land turtles can weigh up to 400-500 pounds and can live for perhaps as long as 150 years. The Galapagos tortoises, made famous by Darwin's observations, are thought to belong to one species, with 11 sub-species. Some live where there is lush vegetation in easy reach; these ones are larger with dome-shaped shells. Others are smaller, with saddle-shaped shells and longer necks and legs which allow them to reach sparser overhead vegetation.
The crocodilian group of reptiles includes 23 species of crocodiles, alligators, gharials, and caimans. There is only one living species of gharial, found in India. Although it has sharp teeth, its main diet is fish that it gulps down whole. Caimans are similar to American alligators; they're actually both in the same family. Caimans are found wild only in South America. Even if most crocodilians look like man-eating monsters, several species don't grow past 4-5 feet. How can you tell an alligator from a crocodile? An alligator's lower teeth are hidden inside when its mouth is closed, but a croc's teeth show. Crocodiles usually have more pointed snouts, as well.
Reptiles, as well as many other animals, have a Jacobson's organ as part of their senses. The animal's tongue picks up airborne particles and chemicals, then sticks its tongue in the Jacobson's organ in the roof of its mouth. The Jacobson's organ analyzes the particles and tells the brain what the animal 'smelled.' Some snakes - boas, pythons, and pit vipers - also have heat-sensitive receptors ('pit' openings) on the sides of their heads.
Did you know that about 4/5 of the world's snakes aren't harmful to people? If you don't live in an Asian or African country, your chances of ever getting bit by a poisonous snake are slim - in the U.S., more people die from insect bites than snake bites. Most species even of poisonous snakes, such as the black mamba, are not aggressive. Other reptiles can be dangerous, too, even if they don't have venom. Crocodilians are strong and have sharp teeth, while Komodo dragons (a large monitor lizard) can bring down a deer!
The majority of reptiles are oviparous, meaning that they lay eggs. But some snake species are viviparous - the eggs are fertilized inside the female's body and the baby snakes crawl out after they hatch, a sort of 'live birth.' There's also one species of snake (the Brahminy blind snake) that can reproduce parthogenetically, without fertilization by the male. All the snakes that hatch this way are females with genetic code identical to their mother.
Many reptiles, including turtles, tuataras, and crocodiles, are male or female because of the temperature their eggs were in the nest. Hotter temperatures produce males, cooler produce females, and in-between temperatures can result in a mix of male and female.
Metamorphosis is the scientific term for a life cycle which includes a larval stage that looks very different from the adult stage; the word means 'change form.' (You can watch metamorphosis firsthand with an inexpensive Frog Hatchery Kit!) An amphibian begins life as a fertilized egg. The female usually lays eggs in water in a string or mass that sticks to vegetation. The male fertilizes the eggs as they are laid. The outer layer of the eggs is a jelly-like material that swells in water, forming a protective coating. The fertilized egg is a single cell that rapidly divides again and again, producing new cells that become the organs of the amphibian embryo. The amphibian hatches into its first larval stage (within 2 to 25 days for frogs, depending on water temperature), as a tadpole or polliwog. At this stage, the animal looks more like a fish than anything else. As the larvae develops, gills form that allow it to breathe efficiently underwater. Its tail grows longer and a fin forms, which allows the tadpole to swim effectively.
The tadpole continues to swim, eat, and grow for at least several weeks before it matures to the next stage. In frogs, the first sign of further development is the appearance of hind legs. Then front legs develop and the tail becomes shorter. Internally, the tadpole's gills are replaced with lungs until finally the tadpole has become an adult amphibian. The mature adult then starts the cycle again by laying or fertilizing eggs.
Some amphibians, especially salamanders, become adults without ever outgrowing the last larval stage. They retain their gills instead of developing lungs, but do have the ability to reproduce. This is called neotony, and can be caused by environmental factors like a lack of iodine.
Even if you don't want to dissect a frog and a snake (or a turtle, for another interesting reptile specimen), you might find the following description of anatomical differences helpful. (You can also find virtual frog dissections online, instead of doing your own.) This is an ideal project for junior high and high school students, although younger kids might be interested, too.
Click the link for a printable snake dissection photo with labeled parts (pdf). Use this as a guide for locating organs.
Read the rest of the project for tips on doing a frog dissection!
How do you tell the difference between a reptile and an amphibian? To help your young children understand the similarities and differences between reptiles and amphibians, make a chart. For older elementary and junior high kids, let them create charts listing differences between different kinds of reptiles or amphibians (e.g., how is a frog different from a salamander?).
Since reptiles and amphibians can be hard to observe in the wild, take a field trip to a zoo or pet store. You might call ahead to see if your kids will be allowed to handle any of the animals. Before you go, ask younger kids what they think a snake feels like. What about a frog? A turtle? Will a frog or a snake feel more 'slimy'? After the visit, discuss the experience. Encourage older kids to investigate feeding habits, make sketches, observe how the animal moves, etc.
If you are handling frogs in the wild, be sure that you have wet hands or hold the animal with a plastic bag. Your bare hands can quickly cause the frog's skin to dry out. After touching any amphibian or reptile, be sure to wash your hands well with soap and water!
To find out more about frogs, do research on one of these topics: what kinds of frogs live in your area? Can you find more than one species of tadpole locally? If so, compare them. What do local frogs eat? How would the mosquito population be affected if there were few or no frogs in a swampy region? Pick a frog or frog characteristic that is interesting to you, and see what you can find out about it. Look for close-up frog pictures in a magazine like National Geographic or on a website.
To see for yourself how an amphibian and reptile differ, compare the external anatomy of two species such as a frog and a snake. You can observe the external anatomy of live ones at a pet store. Or do an online image search: try 'bufo' (part of the scientific name for some frog species), 'bullfrog,' 'poison dart frog,' 'tree frog,' 'garter snake,' 'elipidae' (the main family of poisonous snakes), 'colubridae' (the family with common snakes), and 'boidae' (constrictors).
This is just an overview of some features of frogs and snakes - there's a lot more to learn about them!
Both frogs and snakes (as well as other reptiles) molt, or shed their skin. Frogs change their skin about once a week! Although all reptiles shed their skin as they grow, snakes lose their skin in a whole piece rather than pieces flaking off.
Frogs have a tympanic membrane that can detect sound waves in water or the air and transfer the sound to the inner ear. Snakes have no external ear openings, but they can pick up vibrations through their jaw bones, which transfer to their internal ear bones.
Frog tongues are broad and specially attached so they can be thrust out and catch insects. Snake tongues are narrow and forked, to 'taste' chemical particles in the air.
Have you ever wondered how frogs breathe? When under water, frogs get their oxygen from water that passes through their skin. Capillaries take the oxygen from the skin into the bloodstream. On land, frogs usually get oxygen by taking air through their throats into saclike lungs.
Biggest, Strongest. The king cobra is the longest poisonous snake in the world, measuring in at 10-12 feet! The biggest lizard is the Komodo dragon, almost the same length but much heavier. Although the largest crocodile on record is not a 40-foot croc supposedly found in New Orleans, saltwater or estuarine crocs can grow to about 20 feet in length. (As long as a two story house is tall still is pretty big!) But the reticulated python, the longest reptile in the world, tops that at 33 feet. And anacondas, although not as long, have much more mass - thicker, heavier bodies.
See how their surroundings cause cold-blooded animals' temperatures to adjust! This page has infrared images of animal body temperatures.
Visit the reptiles and amphibians page at the Smithsonian Zoo for facts and pictures.
Many countries have more than 1-2 kinds of crocodilians, shown on this species map.
Search for amphibian species by country.