It is meant to describe an organism that has remained relatively unchanged over millions of years, or one that has no, or very few, close surviving relatives. Example:1. PLATYPUSThe recent decoding of the platypus's genome confirms what we already knew: the platypus is one of the strangest creatures on Earth. It's technically a mammal because it is covered in fur and produces milk, but it comes up short on the requirement that its young be born live (it is one of two mammals which lays eggs). 2. OPOSSUMThe only marsupial in North America, the opossum as we know it is in fact one of the most recent marsupials to evolve, which would seem to disqualify it from this list. But as far as the living-fossil moniker is concerned, the opossum can be included under its umbrella because it has retained many of the features of the earliest known marsupials and so bears a close relation.

Such organisms which remain unchanged since its arrival on the earth .they are still found . eg. limulus

Fossil means remains or impression of prehistoric organisms