LIVING FOSSIL?: Creature Resembling Long-Extinct Trilobite Found in Antarctic Seas

by Richard Poe Saturday, May 19, 2007 9:54 am Eastern Time

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Figure 1. This newly-discovered Antarctic arthropod strongly resembles the trilobite, believed to have been extinct for more than 250 million years.

Scientists are calling it a new species of serolid isopod. But any amateur fossil hunter will see in this newly-discovered creature a strong resemblance to the trilobite — a crab-like arthropod which presumably went extinct more than 250 million years ago, after flourishing for some 251 million years in the primordial seas.

During three Antarctic voyages between 2002 and 2005, the German research vessel Polarstern discovered more than 700 new species of marine life, in frigid depths ranging from 774 to 6,348 meters (about 2,500 to 21,000 feet). The creature shown on the left — identified as a new type of serolid isopod — was one of the exotic beasts found by the Polarstern expedition. (1)

A quarter of a billion years ago, trilobites were among the most abundant life forms on earth.

“If you had been able to scuba dive during the Ordovician period,” writes Richard A. Fortey in The American Scientist, “you would have seen at once that the seas swarmed with trilobites. A few trilobites were as large as dinner plates, many more were the size of modern shrimp, and yet others were smaller than peas. … We have a good fossil record of them because they were the first arthropods to secrete a hard exoskeleton made of mineral calcite. …” (2)

Figure 2. No, this isn’t a trilobite. But this fearsome Anomalocaris likely preyed on trilobites in the Cambrian seas, some 570 to 510 million years ago. (Created by David Quinn, Paleoindustrial)

Figure 3. Now these are trilobites! (created by Dr. Sam Gon III)

The Great Extinction

Figure 4. A trilobite fossil from the Ordovician period (roughly 510-439 million years ago)

Richard Fortey continues: “Trilobites appeared in the fossil record, low in Cambrian strata laid down about 522 million years ago. Within a few million years the trilobites were both abundant and varied. More than 5,000 different genera have now been named, and doubtless many more remain to be discovered. They ultimately died out about 270 million years later, near the end of the Permian period, during the `great extinction‘ that wiped out 95 percent of all species in the Earth’s oceans.”

No one knows for sure what caused the great Permian extinction. Theories run the gamut from possible asteroid impacts to a catastrophic outbreak of volcanoes. All we know for sure is that, when it was over, more than 95 percent of all marine species and about 75 percent of all land species on earth were extinct. Scientists have long believed that the trilobite perished in this catastrophe. (3)

Figure 5. Detail of a trilobite head. Compare its structure with that of the Antarctic isopod at the top of this page.

Perhaps the scientists are right. Perhaps the Antarctic isopod pictured above is unrelated — or only distantly related — to the genuine trilobite, and its resemblance to the fossils merely incidental.

All the same, this writer spent enough time as a lad rambling over limestone deposits in Central New York in search of Cambrian and Ordovician fossils to feel a certain thrill of recognition upon glimpsing the “serolid isopod” pictured above. If scientists refuse to classify this creature as a trilobite, I, for one, would like to know why.

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UPDATE 05.20.07 01:38 PM ET: Attention, readers. Your faithful correspondent has learned, with some sheepishness, that he is hardly the first layman to call attention to the resemblance between the ancient trilobite and certain marine species of the order isopoda still living today.

Indeed, Dr. Sam Gon III, creator of the authoritative trilobites.info Web site, has devoted a special page to “Trilobite Impostors” — modern-day look-alikes whose resemblance to the trilobite can easily fool what Dr. Gon calls (ahem) “the ignorant”.

Ignorant or not, I still insist that anything resembling the serolid isopod found by the Polarstern expedition, had it been discovered frozen in a bed of Ordovician shale, rather than scuttling alive over the Antarctic sea floor, would have been labeled a trilobite without a moment’s hesitation by the most learned paleontologists.

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NOTES

1. Michael McCarthy, “Antarctic Mission Finds 700 New Species“, redorbit.com, 17 May 2007 03:10 CDT; Rebecca Morelle, “Antarctic `Treasure Trove’ Found“, BBC News, 16 May 2007, 21:23 GMT; Deborah Zabarenko, “Southern Ocean Loaded with Carbon Dioxide“, Reuters, 19 May 2007

2. Richard A. Fortey, “The Lifestyles of the Trilobites“, American Scientist Online, September-October 2004, Vol. 92, No. 4, p. 446

3. Hillel J. Hoffmann, “When Life Nearly Came to an End: The Permian Extinction“, NationalGeographic.com, September 2000; “The Day the Earth Nearly Died“, BBC TV, 5 December 2002; “Great Extinction Came in Phases“, BBC News, 1 April 2005, 10:46 GMT

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ILLUSTRATIONS

Figure 1. Photo by Wiebke Brokeland, LiveScience
Figure 2. Animation by David Quinn, Paleoindustrial
Figure 3. Animation by Dr. Sam Gon III
Figure 4. Photo courtesy Hunterian Museum, George Rae collection
Figure 5. Photo courtesy East Midlands Geological Society