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Living Fossils

Living Fossils

Evolution is not a constant but rather an unpre­dictable process. Some undergo multi­ple and significant physical alterations over a span of a few centuries. Others endure millions of years with little change, leaving their present-day form almost a mirror image of a distant ancestor; these latter life forms are commonly referred to as “” and are unique residuals of time.

Enduring Organisms

The present-day coelacanth, chalum- nae, is believed to be a fish from which the first amphibians may have evolved approximately 400 million years ago (mya). The discovery of a living specimen during the mid-20th century caught sci­entists unaware since such fish were thought to be extinct. Through subsequent investigations, the Latimeria chalumnae, which resembles coelacanths from 100 mya, was determined to live off the Comoro Islands at depths of more than 500 feet. Ichthyologists believe that limited competition and a lack of natural predators provided Latimeria chalumnae with a stable environment in which to survive relatively unchanged. Whatever circum­stances made it possible for a coelacanth species to survive, and no matter the distinctive differences between Latimeria chalumnae and its predeces­sors, there is no question of the coelacanth’s status as a living fossil.

Coniferous Trees

Vast grasslands covered much of North America when Native Americans first explored the continent over 12,000 years ago. Even then, coniferous trees, including pine and spruce variants, existed; a great span of time in terms of humanity’s antiquity, but a mere instant in the life of conifers.

Coniferous trees surfaced toward the end of the Paleozoic era, over 200 mya. A plant variety we consider so ordinary today, using pine and spruce for lawn decoration and even holiday fixtures, has an antiquity rivaling dinosaurs, making conifers living fossils hidden in plain sight.

Dragonflies

A multitude of dragonfly species exist today, all of which possess bodies that are as lethal as they are elegant. Dragonflies are predators, subsisting on a diet of mosquitoes, midges, and other small insects. Two sets of strong wings enable them to hover and then accelerate rapidly. Remarkably, these persistent insect-hunters are continuing on an evolutionary trek encompassing more than 300 million years. As for contemporary species, they started surfacing roughly 100 mya. A recognizable form of that antiquity certainly qualifies the drag­onfly as a living fossil.

Ferns

Fern species are as diverse as they are ancient, the variety of fern designs seemingly endless. Yet, such diversity does not mean that modern ferns do not bear any significant resemblance to older forms. In fact, the complex designs of modern ferns mirror those of ferns that appeared approximately 300 mya. Then, as now, ferns endured changing climates and survived while other plant and animal species disappeared. This endurance of fern spe­cies, as potent now as it was millions of years ago, is what earned ferns the title of living fossils.

Goblin Sharks

The infamy of Carcharodon (great white shark) continues to capture the attention of researchers and beach enthusiasts alike. Consequently, our understanding of Carcharodon carcharias has increased dramatically to include a clearer knowledge of its earliest (modern) ancestors, which emerged approximately 60 mya. Yet, with even so lengthy a history, Carcharodon carcharias is far from being an elder among shark species. Today, a number of sharks reflect nearly 100 mil­lion years of relative stasis, earning them the title of living fossil. Of these, owstoni (the ) is arguably the most unique.

With a flat, extended snout positioned above its mouth, resembling a horn or similar projection, Mitsukurina owstoni is an oddity. With specimens first being acquired and described at the end of the 19th century, Mitsukurina owstoni‘s similarity to ancient sharks (long believed extinct) quickly became apparent. Mitsukurina owstoni‘s ancestry was ultimately traced to the Cretaceous period, extending the terrestrial presence of similar species to over 100 million years.

Horseshoe Crabs

The armored body of the horseshoe crab, Limulus polyphemus, is hard and nearly impene­trable. After an examination of the fossil record, it is also apparent that the horseshoe crab’s design is long-lived.

Horseshoe crabs appear ancient, complete with an armor-plate-covered body reminiscent of several dinosaur species. Yet, given the design of horseshoe crabs, it is astonishing how resilient these creatures are. Although very resilient, horseshoe crabs do suf­fer continual fluctuations in their environment, enduring varying moisture and salinity levels and even high levels of pollutants. The casual observer of these creatures will undoubtedly be astounded by the reality of horseshoe crab hardiness. Yet, when looking at the fossil record, the durability of these creatures becomes understandable.

The current species of horseshoe crabs are quite similar to ancestors living 300 mya. For such a biological design to endure that long, horseshoe crabs must be engineered well, considering the dra­matic changes the planet continues to undergo.

Future Living Fossils

Archaeologists and paleontologists use picks, shov­els, and trowels to uncover the past and reveal fossils of species that once inhabited the planet. Living fossils, such as the species aforementioned, provide a similar glimpse into the past, and in the process make the remote past seem more tangible, more real. It is inviting to speculate which of the species that are common today will become the living fossils of the distant future.

Neil Patrick O’Donnell

See also Coelacanths; Extinction and Evolution; Gingko Trees

Further Readings

Ellis, R. (1976). Book of sharks. New York: Grosset & Dunlap.

Maisey, J. G. (1989). Evolution of the shark. In J. D. Stevens (Ed.), Sharks (pp. 14-17). New York: Facts on File.

Parsons, G. R., Ingram, G. W., Jr., & Havard, R. (2002). First record of the goblin shark Mitsukurina owstoni, Jordan (family ) in the Gulf of Mexico. Southeastern Naturalist, 1(2), 189-192.

Ward, P. D. (1992). On Methuselah’s trail: Living fossils and the great extinctions. New York: W. H. Freeman.

Ware, J., May, M., & Kjer, K. (2007). Phylogeny of the higher Libelluloidea (Anisoptera: Odonata): An exploration of the most speciose superfamily of dragonflies. Molecular Phylogenetics and Evolution, 45, 289-310.

What do you think?

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