Question

What is fossils ?
OR
Define homologous organ​

Answer 1

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Fossils are the geologically altered remains of a once-living organism and/or its behaviour. There are two main types: body fossils represent all or part of the organism's body, and trace fossils show evidence of the organism's behaviour. Scientists who study fossils are called paleontologists.

⠀⠀⠀⠀⠀OR

Homologous organs are defined as the organs of different animals that are having a similar structure but differ in their functions. The structure of the two different animals resemble but the functions of their organs vary.

Answer 2

Explanation:

Homologous organs are those organs which have the same structure and embryonic origin but perform the different functions. For example, forelimbs of whale, bat, deer, rabbit have the same structure but are modified in different ways to perform locomotion in different ways. Such kind of structures give rise to divergent evolution. 

Fossils

Fossils are the remnants of the past organisms which get buried in sedimentary rocks. Different fossils are formed in the different aged rock sediments. The study of fossils existing in the different rock layers indicate the time period when they existed. Thus different life forms have been formed at different times in the history of the earth. Fossils indicate how the evolution took place leading to the formation of complex life forms from simple ones by the gradual process. For example, fossil bird Archaeopteryx is considered as a connecting link between reptiles and birds indicating that birds evolved from reptiles. It shows the presence of characters of both birds and reptiles like the presence of teeth, wing feathers, clawed toes .Fossils are the preserved remains, or traces of remains, of ancient animals and plants