The Amphibians

The Amphibians - The Amphibians the class amphibian Class Amphibia(Greek both or double lives o Over 3,900 species Represents the most dramatic

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The Amphibians- the class amphibian Class Amphibia (Greek both or double lives) o Over 3,900 species Represents the most dramatic event of evolution of animals: water to land Movement was difficult because the land is a lot more dangerous than the water Brought water with us to stay alive, like a safety net. As land inhabiting amphibians were evolving we had to see structural, functional, and behavioral changes in the organism so they could survive on land and maintain body systems. Most animals are made of mostly water Cellular activities have to take place in water o Order Caudata – Salamanders Tailed amphibians Lease specialized and the most aquatic of the amphibians o Order Anura – frogs and toads Tailess amphibians Largest and most biologically successful group of amphibians o Order Gymnophiona – caecilians Tropical in distribution Worm like in appearance Highly secretive in their life cycles Odds and Ends before this section o All animals are composed of mostly water o All cellular activities occur in an aqueous medium o All vertebrates are descendants from the same evolutionary branch
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o Amphibians are not the first organisms to move out onto the land Plants initially made the movement in the Ordovician (505 – 440 mya) Insects made the move during the Silurian (440 – 407 mya) Pulmonate snails (had lungs) made the move onto the land during the Devonian about the same time as the Amphibians (407 – 360 mya) o We want to follow the amphibian story because it is the most relevant to us o Every body system in amphibians had to change in order for them to be able to function on land Aquatic vs. Terrestrial Environments o Oxygen content Aquatic 3-9 mL oxygen/ L of water. 20x less oxygen available in water than in the air Oxygen diffuses a lot slower in the water o Aquatic animals use a lot more energy to get oxygen from the air Terrestrial 210 mL oxygen/ L of air o Density Aquatic 1000x greater than density of air Harder to move in the water o 50x more viscous than air High density supports the animals body o Buoys up the animals’ body Whales were too large and the pressure in the body itself was too much to handle Water was able to buoy the weight.
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Terrestrial Need for strong limbs o Skeleton must be restructured for the animal to move around on the surface o Temperature Aquatic Water has a high specific heat so there is little fluctuation in the temperatures of natural bodies of water Living in the water gives more stable temperatures. o Water buffers temperature changes on the land Have to put in a lot of heat to warm up and take out a lot to cool off Terrestrial Land can change from freezing to thawing to warm throughout the day They can also easily dehydrate if there is no water More dangerous consequences. Evolution of endotherms was something that had to happen so that
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This note was uploaded on 09/19/2011 for the course 1 101 taught by Professor Larrydavid during the Spring '11 term at South Carolina.

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The Amphibians - The Amphibians the class amphibian Class Amphibia(Greek both or double lives o Over 3,900 species Represents the most dramatic

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