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    Home / Science lessons / Reptile & Amphibian Basics
    • Reptile & Amphibian Basics

      Whether you hate frogs and snakes or are fascinated by them, we hope you'll find something interesting in this article! Reptiles and amphibians have many physical differences, but they can be grouped together for a couple of reasons. Both are cold-blooded or "ectothermic," which means their body temperatures adjust to the temperatures of their surroundings, rather than maintaining one set body temperature like humans do.  So when they get too hot, they jump in cool water or hide in the shade. When they need to warm up, they bask in the sun or burrow into mud. In colder climates, reptiles and amphibains hibernate during the winter.

      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.

      Reptiles

      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.

      Amphibians & Metamorphosis

      Amphibians, the class of animals that frogs and toads belong to, are unique in their ability to live both on land and in the water. They have moist skin that water can pass in and out of, and most of them spend at least part of their life - the tadpole-like larval stage before they mature - in the water. The name Amphibian literally means "both life." In addition to frogs and toads, amphibians include salamanders (newts are in that group) and caecilians, burrowing worm-like animals that have jaws and teeth.

       

      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." 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.

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