i) To know about the extinct or previously existing animals we can look at the fossils. Fossils and not just the buried teeth, skull and bones but can also be the footprints of any animal are the outlines of the Fallen leaves or plants which under the pressure of the layers of soil becomes preserved as fossils. The study of fossils is known as paleontology.

ii) Connecting links are the organisms which behave as a link or connection to two different classes or species.

Example: One very common example is of Archaeopteryx. It is a connecting link between

Aves (birds ) and reptiles. It has common features of both the classes. Some features of birds include that they can fly but they also have teeth and tail like the ones present in the reptiles.