Time
Fossils and the Scientific Process
Life through Time
Evolutionary Milestones
Extinctions
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Fossils Glossary
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Link to Dinosaur Walk
Link to Prehistoric Life
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'Living fossils'
'Living fossils' are of interest to palaeontologists because, being so little changed in form from their ancestors, they provide information on the anatomy and life habits of the fossil representatives.
The term 'living fossil' was first coined by Charles Darwin to refer to the ginko tree, which has distinctive wedge-shaped leaves that are almost identical in the single living species and in fossils as old as Triassic in age (about 240 million years old). Used in this sense, a 'living fossil' is an organism that has remained relatively unchanged over a long span of geological time, surviving mass extinctions that have affected other groups. Other such 'living fossils' include the inarticulate brachiopod Lingula, with a fossil record extending back at least 550 million years to the Cambrian Period; the group of caterpillar-like arthropods called onychophorans, widely distributed though uncommon in damp tropical and temperate forests at the present day, and with a fossil marine representative in the Middle Cambrian Burgess Shale of British Columbia; the horseshoe crabs or xiphosurans, the living forms found today in the Indo-Pacific region and along the east coast of North America being very similar to fossilised representatives from the Triassic; bivalve molluscs belonging the family Trigoniidae, which was widespread in the Mesozoic Era but in the Cainozoic Era became restricted to Australian waters where representatives still live today; Queensland lungfish Neoceratodus, belonging to a group with a fossil record going back to the Devonian and scarcely distinushable from the Triassic lungfish Ceratodus; crocodiles, virtually unchanged today from fossilised remains known from the Jurassic; and the lizard-like tuatara or Sphenodon of New Zealand, whose ancestors were contemporaries of the dinosaurs but survived the mass extinction at the end of the Cretaceous Period.
There is another sense in which the term 'living fossil' is sometimes used, and that is to refer to organisms that were long considered extinct but subsequently found to have one or a few living species. An example of a 'living fossil' in this sense is the coelacanth fish Latimeria, discovered off the east coast of Africa in 1939. It is the sole survivor of a lineage of lobe-finned fishes, the crossopterygians, that were previously believed to have died out in the Cretaceous.
References:
Gordon, T. & Jablonski, D. 1979. Living fossil. In Fairbridge, R. W. & Jablonski, D. (eds), Encyclopedia of Paleontology, Dowden, Hutchinson &Ross, Inc., Stroudsberg, Pennsylvania, 419-422.
Fisher, D. C. 1990. Rates of evolution - Living fossils. In Briggs, D. E. G. & Crowther, P. C. (eds), Palaeobiology. A synthesis, Blackwell Scientific Publications, Oxford, 152-159.
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