What is a living fossil?
We use the term "living fossil" to describe a lineage that have survived, relatively unchanged, for millions of years. Most of these organisms have endured mass extinction events and exist today as living relics of ancient life. These "living fossils" are important because they can provide clues about earth's history. Studying these ancient organisms also can help us to understand how modern species first evolved and to recognize patterns of evolution that continue to influence our changing world.
Image: Wong Maye-E / Associated Press
The
nautilus (top left) is the only living member of an otherwise extinct group of cephalopods. Below, fossil evidence demonstrates that extinct ammonites, close relatives of the nautilus, were once abundant marine animals.
With their hinged exoskeleton and hardened tail (telson), the curious-looking
horseshoe crab appears the very epitome of a living fossil. In fact, these organisms belong to a primitive group of marine arthropods. Horseshoe crabs are the only of their kind to have survived the mass extinction that brought about the end of the dinosaurs, as well as half the planet's marine invertebrates.
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| Image: Great Lakes Image Collection |
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| Image: University of Chicago Medical Center |
Dating back at least 360 million years, the eel-like
lamprey is the most primitive of all vertebrates. Unlike modern fish, the lamprey is a jawless parasite that lacks scales and paired fins. Lampreys are of interest to scientists, who hope to understand how these ancestral fish fit into the evolutionary scheme that gave rise to the diversity of modern vertebrates.
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| Image: M McKelvey/ P Rismiller |
The
echidna (bottom right) and
platypus (top right) are the only living representatives of the group of egg-laying mammals called
monotremes. These organisms are believed to have diverged from the mammalian lineage some 150 million years ago, and are distinct from two mammalian sister groups, the marsupials and the placental mammals. Monotremes are important for answering fundamental questions about the common ancestor to these three distinct mammalian groups.
