The Evolution of Amphibians

The Evolution of Amphibians — page 3 — During the Devonian period Earth was warm and wet When the animal was in shallow water it used its front flipper like limbs to pull itself along Since its limbs had formed in water its back legs probably weren't strong enough to support its weight on land So this animal made its way across sand and rocks with just its front limbs Ichthyostega was one of the first tetrapods to make the transition from water to land Tetrapods are animals with four limbs including modern mammals birds reptiles

The Evolution of Amphibians — page 4 — and amphibians Amphibians are members of the class Amphibia which includes extinct and modern amphibians Ichthyostega is one of the earliest ancestors of modern amphibians Because it had the characteristics of both a fish and a tetrapod Ichthyostega is known as a fishapod Like a fish it had gills small scales on its body a dorsal fin on its tail and ears that worked best underwater But like a tetrapod it had a set of lungs a rigid skull a strong rib cage and large bones inside four thick limbs Its joints elbows wrists knees and ankles were also similar to those of tetrapods And it had seven digits on each of its feet Ichthyostega lived during the Devonian period 419.2-358.9 MYA The Devonian had a warmer climate than today Oceans covered more than 85 percent of Earth and landmasses were grouped into supercontinents 2 This period is also known as the Age of Fishes because of the large variety of fish in the seas It is when the first amphibians were born WHAT ARE MODERN AMPHIBIANS Modern amphibians are animals that can live both in water and on land In fact the word amphibian comes from the Greek amphibious which means living a double life Most amphibians begin life in the water and move onto land at maturity

The Evolution of Amphibians — page 5 — There are more than 7,900 species of amphibians in the world and they can be broken up into three main groups Frogs comprise the largest group and they are of the order Anura They have short bodies with no tails and their hind legs are strong longer than their front legs and ideal for leaping Salamanders make up the second largest group and they are of the order Caudata They have tails and their front and back limbs are about the same size Finally the smallest group of amphibians is called the caecilians of the order Gymnophiona Caecilians resemble large earthworms and have no limbs Their bodies are ideal for burrowing GOLDEN POISON FROG Many frogs produce a poison in glands of their skin to keep predators at bay But the golden poison frog of Colombia produces one of the deadliest ones Named for its often yellow color it can also be orange or pale green Measuring approximately one to two inches 2.5-5 cm in length it can produce enough poison to kill ten adult humans

The Evolution of Amphibians — page 6 — CLASSIFICATION Golden Poison Frog Phyllobates terribilis DOMAIN Eukaryota This domain includes plants animals and fungi These organisms are grouped together because their cells each have a nucleus a cell structure that contains the DNA KINGDOM Animalia All animals including mammals and amphibians are in this group PHYLUM Chordata Organisms in this phylum have a nerve cord down their backs supported by a rod of cartilage at some point in life All animals with spines including mammals and fish are in this group CLASS Amphibia This class contains caecillans frogs and salamanders ORDER Anura This order contains frogs and toads FAMILY Dendrobatidae Frogs in this family are typically small poisonous and have colorful skin GENUS Phyllobates These small poisonous frogs are active during the day and live in Central and South America SPECIES terribilis Golden poison frogs are often yellow and live in the Amazon rain forest Taxonomic classification is the science of identifying living things grouping them together and naming them When this is done each organism is assigned a place in eight different categories ranging from domain the most general category to species the most specific category When the scientific name of an animal is given it includes the genus which is capitalized and the species which is not Golden poison frogs are Phyllobates terribilis Scientific names are often abbreviated after first use P. terribilis

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