Birds

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being argued. Most people believe that
birds evolved from reptiles. Because of birds mainly delicate bones, few fossils
have been left behind for scientists to study. The earliest bird fossils come
from archaeopteryx. The fossils that have been discovered from archaeopteryx
include six partial skeletons and one single feather. Archaeopteryx , unlike
modern birds, had teeth, a reptile like tail, and three claws on each wings.
Scientists think it could fly, but only weakly.
Approximately 85 species and 50 sub species have become extinct in the
last 300 years. Over half of them occurred in the 1800�s. Another thirty percent
occurred in the 1900�s. Over ninety percent of these extinction�s were island
forms, which are particularly vulnerable to human interference. Destruction of
habitat is the biggest cause of extinction. Other causes are the introduction of
predacious animals, and disease plays it�s part too.
The respiratory system in birds serves to transfer oxygen to the ...

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