 |
|
|
|||
|
|||
|
|||
|
|
|
AMPHIBIANS AND REPTILES TAXONOMY AND CHARACTERIZATION Taxonomy and Characterization class activity may be done in a variety of ways. For example, a taxonomy and characterization exercise may be undertaken after study of each of Class (Amphibians, Reptiles, Birds and Mammals.) Alternatively, the exercise may be undertaken after the four Classes have been studied. The method to adopt may be adapted depending upon situation. This can also be adapted to Georgia wildlife by selecting the animals from Georgia Wildlife Site. Objectives:
5-6 class periods (inclusive of lecture and activity) Background:Chordates are any member of phylum Chordata. All members of phylum chordata possess certain features at some time in their life cycle, like a dorsal supporting rod called the notochord, pharyngeal apertures (gill slits), and a dorsal nerve cord running along the back. Chordate bodies consist of a body wall which encases the gut. The body is usually long and bilaterally symmetrical (right and left halves of the body similar). The mouth and sense organs are located in the anterior and the anus at the base of the tail. The phylum Chordata is subdivided into three sub-phylums: Vertebrata or Craniata (amphibians, reptiles, birds, mamals, fishes and lampreys), Cephalocordata or Acrania (lancelets or amphioxus), and Urochordata or Tunicata (Tunicates). Tunicates are small marine animals, length ranging from 1 millimeter to 20 centimeters. Tunicates are either benthic (bottom dwelling) or pelagic (floating). Typical length range is between 1 to 5 centimeters (0.4 to 2 inches). Cephalopods are small, fishlike marine invertebrates, probably closest living relatives of vertebrates. Their size ranges from 1 to 3 centimeters. However, the vertebrates have the greatest size variation, ranging from tiny fish to the whales, the largest animal ever to have existed. Any animal of the subphylum Vertebrata is characterized by the presence of a vertebral column or backbone. Vertebrates are unique in possessing an internal skeleton, formed of either cartilage or bone, or both. The skeleton allows vertebrates to achieve large size; most vertebrates are larger than invertebrates. Vertebrates are also characterized by a muscular system and a central nervous system partly enclosed within the backbone. The subphylum Vertebrates is one of the best known of all groups of animals. Its members include the classes: Agnatha (primitive, jawless fishes - lampreys and hagfishes), Chondrichthyes or Selachii (cartilaginous fishes - sharks, skates, chimaeras, and rays), Osteichthyes (all bony fishes, includes the 20,000 species and more than 400 families of modern bony fishes, as well as a few primitive forms, but excludes Agnatha and Condrichthyes); Amphibia (amphibians); Reptilia (reptiles); Aves (birds); and Mammalia (mammals). AmphibiansClass Amphibia is one of eight vertebrate classes. The word Amphibian is derived from two Greek words, amphi meaning both, and bios meaning life. This double life refers to the two phases, an aquatic larval or tadpole stage that metamorphoses to a terrestrial adult stage, in life cycles of most amphibians. Despite this distinction, some species spend their lives entirely on land and some entirely in water. Amphibians are descended from fish (lobe-fin fish or the lungfishes) some 408 - 387 million years ago. Primitive amphibians are considered intermediary in evolutionary development between fishes and reptiles. Modern amphibians, however, are not truly transitional in their morphology and do not exemplify the intermediate status. They have achieved a variety of modifications, which are specific adaptations to their environments; skin is such an example. Amphibian skin is kept moist by mucus-secreting glands that help respiration and maintenance of water balance. Amphibians were the first vertebrates to move from an aquatic environment to land, and they are ancestors of all reptiles, birds, and mammals. Most amphibians are carnivorous, i.e. meat eating animals. They feed primarily on insects, mollusks (snails) and other tiny invertebrates. Amphibians are cold-blooded vertebrate animals, i.e. they cannot regulate their body temperature. They are found largely in sub-tropical and tropical climates, and they do not live in very cold climates. Amphibians are known to live in a wide range of habitats, viz. swamps, forests, grasslands, mountains and even deserts. However, all require moist fresh water environments, and cannot live in brackish or saltwater habitats. Amphibians mostly lay jelly-covered gelatinous eggs, called spawn, in the water. These eggs have no hard shell and must remain moist, otherwise the young amphibian inside the egg may die. These eggs hatch and the young amphibians remain in water (the aquatic larval stage - for example the familiar tadpoles of frogs and toads) until they metaphormose into adults and emerge from water to live on land. They never, however, live far away from water. Almost all the adult amphibians have limbs, but when young they do not have limbs. When young, in an aquatic larval stage, amphibians breathe through lungs, and when mature they breathe through lungs. They also breathe through their skin. That is why they have a moist slimy skin to absorb Oxygen. There are about 4,450 known living species of amphibians worldwide, with about 245 species known to live in North America. These known living or extant species of amphibians can be divided into three orders (living): Apoda or Gymnophiona (caecilians), Caudata (Salamanders and newts), and Anura (frogs and toads). These three orders differ markedly in structure, and they vary greatly in size. Caecilians (Apoda) are burrowing, wormlike animals that have a simple intestine, and minute eyes buried in a smooth skin. These animals have no limbs and practically no tail, and are mostly confined to moist habitats in the tropics. The length of Caecilians varies from 112 millimeters (4.37 inches) to 1,520 millimeters (59.28 inches). The salamanders and newts prevalent in the southeastern United States and in Mexico, form the second order, Caudata. Salamanders have forelegs and hindlegs of about equal size, a long tail, smooth skin, a neck, and possess teeth on the jaws and roof of the mouth. The sirens are one of the two aquatic genera of salamanders that remain in water with gills. They breathe through gills or gulp air at the surface. These aquatic salamanders have front legs, but no hind limbs. Tail fins assist locomotion. The size (length) of salamanders varies greatly. The smallest is a terrestrial species found in Mexico with a length of 27 millimeters (1.06 inch), and the largest is the giant aquatic salamander found in China that reaches a length of more than 1.5 meters (5 feet). Order Anura, comprising frogs and toads, forms the third order and largest group of amphibians. Animals in order Anura are distinguished by their lack of a tail, large eyes, and a powerful pair of hind legs larger than their front legs, adapted for hopping and swimming. They have teeth, usually in the upper jaw. The glandular skin is generally smooth and soft, but is occasionally dry and rough in terrestrial species. The smallest anuran is Brazilian brachycephalid with a length of 9.8 millimeters (0.38 inch). The largest anuran is the West African goliath frog, which measures 300 millimeters (11.7 inches) in length and weighs 3.3 kilograms (7.28 lbs). Reptiles Reptiles are vertebrate animals belonging to the Class Reptilia (meaning "to creep") that includes the crocodiles, alligators, snakes, tortoises, turtles and lizards among the living, and dinosaurs, pterosaurs and ichthyosaurs among the extinct. In evolutionary development, reptiles are believed to be intermediate between amphibians and warm-blooded vertebrates like birds and mammals. Reptiles characteristically have scales (or modified scales, shells) on their body instead of hair or feathers; breathe air with lungs; internally fertilize through mating; and are oviparous (the female lay eggs in which the young develop), though some snake and lizard species may be viviparous (give birth to young). Strictly speaking, they are not truly viviparous but are ovoviviparous, because the embryos develop with their shells or shell membranes intact and are nourished wholly by the yolk, unlike the mammals. Also, characteristically, reptiles are cold-blooded (ectothermic), i.e. they cannot regulate their body temperature: when in sun the body temperature goes up and when in shade it goes down. The reptiles thus regulate their body temperature by behavior, either by basking in the sun to warm their bodies, or by moving to a cover of shade to cool. That is why we don't see many turtles, lizards or snakes in winter. Some reptiles like tortoises (which live on land), turtles (which live in water) and crocodiles have small and short limbs with claws, while snakes do not have limbs at all; they move on their bellies. Limbs of turtles and crocodiles are similar to flippers, which help them move in water. All reptiles are carnivorous, they eat any type of meat ranging from large mammals such as deer to insects and eggs. However, some turtles and lizards are also known to be herbivores. Some reptiles, such as lizards, may superficially be similar to some amphibians, such as salamanders. The difference is that reptiles characteristically have dry skin with few or no glands while the amphibians have slimy skin. Reptiles live all over the world and are widely distributed throughout the warm and temperate regions, but most abundant and diversified in the tropics due to their cold-bloodedness. Most lizards and snakes live on the ground, although some may be found in trees, in the ground or in the water. Reptiles may range in size from the British Virgin Island gecko (the smallest lizard at only 18 mm or 7/10th of an inch in length) to the anaconda snake (biggest snake which can exceed 9m or 30 feet), and estuarine crocodile (biggest reptile which can exceed 7m or 27 feet). It is estimated that there are about 6,550 living species of reptiles worldwide. Currently, some 301 species of reptiles are recognized to live in North America north of Mexico. The Class Reptilia is composed of four orders, of which species from only three orders are found in North America. They are Crocodilia (crocodilians), Testudines (Turtles), and Squamata (amphisbaenians, lizards and snakes). The Order Rhynchocephalia is found only in New Zealand, and has only one species. Venomous reptile species cause little harm to humans except in a few cases, though people fear them and often kill them when encountered. Although reptiles are not an important food source, in certain parts of the world they are hunted for food. Also, turtle eggs are a food source for many human societies living on the coasts. However, reptiles are hunted primarily for their skins, as they are valued for their leather products. As a result, many species have become extinct. Activity Materials required: Printouts of photographs. (This can be done in two ways. Get the prints of animals from the web sites listed below, a color printer may be better than black and white printer. Or, alternatively ask students to bring a given number of pictures of animals.)
Hanging in the Habitat: A Game about Animals in an Urban Habitat. Games are on BlueJay, Squirrel, Salamander and Garter Snake. Endangered Species Unscramble Game Endangered Species Matching Game Risky Critters (Game on wildlife and endangered species) INTERNET RESOURCES Internet Resources on Chordata: Encyclopaedia Brittanica Chordate Site Encyclopaedia Brittanica Vertebrate Site Glossary on Animals + Links to Animals related web site A Useful site on Amphibians, Animal, Bird, Fish, Game, glossary, Mammal, Reptile, and Internet link resources Critter Corner (Amphibians, Birds, Fish, Insects, Other Invertebrates, Mammals, Reptiles, Habitats, Endangered species, Alien Invaders - Wisconsin state related) All about Nature (animals - natural history and descriptions, biome): A very useful site - a must source for teachers) General facts on Amphibians Amphibians site (General) Georgia Amphibians (Georgia Wildlife Web) Encyclopaedia Brittanica Amphibian Site Amphibians (A good site on frogs, toads, salamanders, newts and sirens Protected Amphibians of Georgia General facts on Reptiles Encyclopadia Brittanica Reptiles Site Georgia Reptiles (Georgia Wildlife Web) Reptile (General and Printouts) Protected Reptiles of Georgia |
||||||||||||
|
Visit Our Partners:
|
|
|
|
|
|
|
||
|
