|Three concepts are important in the study and use of fossils:
(1) Fossils represent the remains of once-living organisms. (2)
Most fossils are the remains of extinct organisms; that is, they
belong to species that are no longer living anywhere on Earth.
(3) The kinds of fossils found in rocks of different ages differ
because life on Earth has changed through time.| |Stratigraphic
ranges and origins of some major groups of animals and plants.|
|Scientists look for ancestors and descendants through geologic
time. The fossil Archaeopteryx lithographica was a Jurassic
animal with the skeleton of a reptile, including fingers with
claws on the wings (solid arrows), backbone extending into the
tail (open arrow), and teeth, but it was covered with feathers.
We can see fossils of many other reptiles in rock of the same
age and even older, but Archaeopteryx lithographica is the
oldest known fossil to have feathers. We conclude that this
animal is a link between reptiles and birds and that birds are
descended from rept