The Evolution of Amphibians

The Evolution of Amphibians — page 1

The Evolution of Amphibians — page 2 — CHAPTER ONE Out of the Water Approximately 360 million years ago MYA in what is now Greenland a brawny animal about three feet 1 m long swam in a river Ichthyostega looked like a short alligator or a large iguana but it had a thick neck and a wide head Using its four squat limbs and tail it propelled itself through the currents eating small fish and breathing with its gills Sometimes it walked along the bottom of the river and sometimes it left the river entirely and stepped onto land How did it do this Why did it leave the water Perhaps there was a long rainy period and the animal found itself in the shallow waters of a floodplain Maybe it just wandered onto dry land An artist depicts what Ichthyostega may have looked like

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

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