A living fossil is an organism which represents the one of the few, if not the only, surviving members of a taxonomic group, with no close living relatives. One well known example of a living fossil is Ginkgo Biloba, a tree which is literally in a class by itself. Like many other living fossils, Ginkgo is also remarkably similar anatomically to older relatives in the fossil record. In fact, a casual comparison of a living Ginkgo and a fossilized tree can yield few obvious differences.
This term is used somewhat ambiguously in the scientific community, and there is some debate over the exact classification of living fossils. Many of these organisms are mistakenly called “primitive” by casual observers, since they may have archaic anatomical features or quirky biology, but these organisms are far from simple. “Primeval” might be a better term, since a living fossil is a member of a small group of creatures which have endured several major extinction events and a dramatically changing global environment.
Some other examples of living fossils include monotremes like the platypus, organisms which lay eggs, but lactate to feed their young. Coelacanth fishes are also living fossils, along with horseshoe crabs, horsetails, and opossums. Some of these animals have very small a limited ranges, and they are extremely vulnerable to environmental pressure, while others are widely distributed and they have apparently found secure environmental niches to inhabit.
A living fossil is not quite the same as a so-called “Lazarus taxon.” A Lazaurs taxon is a taxonomic group which disappears from the fossil record and then reappears, essentially rising from the dead. The scientific community has discovered several examples of Lazurus taxons, in the form of animals which were thought to be extinct and later discovered alive; the Dawn Redwood of China is one such example. In the fossil record, there are a number of explanations for a Lazarus taxon, as the conditions for fossilization must be perfect, and it is possible that gaps do not always mean that a species disappeared.
The study of living fossils can reveal interesting information about the evolution of life on Earth. These creatures must be extremely hardly, so although some of them look and act bizarre, scientists believe that they must be doing something right to have survived for so long. A living fossil is also simply interesting, demonstrating a clear connection between the fossil record and animals which are currently alive; there is something quite amazing about seeing a horsetail fern and knowing that these plants looked exactly the same millions of years ago.