What does the term 'living fossil' commonly refer to?

The term 'living fossil' commonly refers to a species that has remained relatively unchanged over millions of years. This concept highlights organisms that have persisted through extensive geological time while exhibiting very little morphological variation compared to their ancient relatives, thus providing a unique glimpse into the past.

For instance, the coelacanth, a fish thought to be extinct for about 66 million years, is called a living fossil because it resembles fossils dating back to the time of the dinosaurs. Living fossils serve as critical biological and evolutionary studies, as they help scientists understand how species adapt—or do not adapt—to changing environments over geological timescales.

This understanding distinguishes living fossils from the other potential options. A fossil that can still be found in its original habitat does not accurately describe a living organism, as fossils by definition are the remains of past life that are no longer living. An extinct species that is still studied pertains to organisms that do not exist today, thus cannot be termed living fossils. Lastly, a fossil that shows significant evolutionary changes implies that the organism has undergone considerable change, which directly contradicts the essence of a living fossil's characteristic of stasis over time.