Essay Tetrapods

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The early Devonian period is largely considered to be a world of a diverse array of lobe-finned fish, including lungfish, coelacanths, and bony fish. Over the course of time, vertebrates made evolutionary strides with provided them with the ability to travel on land. Coelacanths developed a single boned shoulder girdle, lungfish developed paired fins, and sauripterus developed the major structures on the arm (humerus, radius, and ulna). As these developments progressed and environmental pressures were amounting in aquatic environments, vertebrates began to venture onto land. Sometimes it was for short excursions, sometimes a bit longer. A major step in vertebrate evolution was the advancement of the tetrapod, a vertebrate animal with …show more content…

Many species are completely aquatic during the juvenile part of the lifecycle. For example, frogs have to reproduce in water because amphibian eggs do not have the protection of the amniotic sac. As a result, the adults must return to a water source to reproduce. As tadpoles grow into adults they form limbs that allow them to walk on land. Because of the restriction to semi-aquatic environment, the tetrapod structure of amphibians is not as diverse as the other classes of tetrapods. However, there are groups that deviate from the norm by a lot. Caecilians are limbless amphibians. At first glance they do not look like tetrapods but the lack of limbs is a derived secondary characteristic. Their bodies have adapted for burrowing in the ground. Reptiles, the next tetrapods to emerge, were a very successful version of amphibians. As opposed to amphibians, reptiles did not require water for the reproduction process they produced shelled amniotic eggs to protect their embryos from the environment. Due to the reduced dependence on water, reptiles were able to explore many new environments and as a result their limbs evolved in a variety of ways. Crocdylotarsians developed a “normal ankle” which swings to the side when walking, making walking slightly more efficient. Dinosaurs developed a hole in their hip socket that allowed them to stand upright and to move significantly faster. Another way some terrestrial reptiles

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