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Living fossils

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Have you ever heard the phrase "living fossil"? Do you know what it means? Sounds strange. A fossil is generally thought of as something very old and dead, not living. So what's going on?

The Denver Museum of Nature and Science defines a fossil as being any evidence of ancient life (animals, plants, tracks, footprints), which can be as young as 10,000 years and as old as 3.5 billion years. So what is a living fossil? Let's start by looking at DiscoverySchool.com, a site for kids. It defines a living fossil as being a prehistoric animal species, generally one that lived during the time of the dinosaurs, that continues to survive in its ancient form today. Are living fossils only comprised of animal species? Looking at the site eNature.com, you will see that the definition for a living fossil can be expanded to include birds, fishes, plants, reptiles and amphibians and seashore (clams, oysters etc). This definition is somewhat general and includes a lot of species. But some restrict the definition even further. There are a few species that are termed "classic" or "true" living fossils. A classic or true living fossil is one that has only been known from the fossil record until a living representative was discovered or a single living species with no close relatives, but which is the sole survivor of a once large and widespread group in the fossil record. An example of the first instance is the Coelacanth , a 400 million years old fish. The Coelacanth was thought to be extinct until rediscover in 1938. An example of the second instance is the ginkgo tree, which is thought to have changed little in over 100 million years and to have been food for the dinosaurs.

Here are some other species that are thought of as living fossils but not true or classic:

The crocodile has been on the Earth for more than 200 million years.

The horseshoe crab has changed little over the past 250 million years.

The cockroach has been around for approximately 350 million years.

The cycad has been around for more than 200 million years and was munched on by the dinosaurs. It has been speculated that cycads, which are high in carcinogens, could be the cause of cancer in dinosaurs.

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