Bird skeletons are very delicate, and therefore, difficult to be preserved. The bones of the birds are soft. The small animals are very prone to physicochemical as well as biological decay. This is why the fossil record of bird is incomplete and well-preserved fossils of birds are rare to find, except at a few unusual sites.
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Answer:
Multicellular eukaryotes evolved from unicellular prokaryotes by the process of endosymbiosis
Explanation:
All living beings have evolved from three groups of animals closely related with each other.Domains: Archaea,bacteria and eukarya.the archaea and bacteria are unicellular organism surrounded by single cell water and and coiled stand of DNA. Eukaryotic cells are more complex and with a linear strand of DNA which is in the nucleus. Actually mitochondria which had evolved from a free living bacterium which was swallowed by another cell. The host cell benefited from the chemical energy that mitochondria produced and mitochondria in turn is benefited to be inside the protected environment. Mitochondria is the main organelle which the multicellular eukaryotes with unicellular prokaryotes.
The are coded in the arrangement of either chromosones or DNA.
D oxygen there was no free oxygen on the earth
