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Fossil Friday- giant trilobites from Portugal
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Photo credit: Artur Sá
Recently we reported on Isotelus rex being the largest of the trilobites. Now it appears it may have been dethroned. Recent finds published in the journal Geology tell of more giant trilobites from Portugal. Fossils of Ogyginus forteyi and Hungioides bohemicus are found in slabs of rock from a slate quarry in groups numbering in the thousands. Most of the specimens are over 30 centimeters (1 foot). Elsewhere in Spain and Portugal it is rare to find trilobites over 10 centimeters long.
It is hypothesized that the trilobites may have been huddled together for protection after they molted. Modern arthropods are vulnerable while their new exoskeleton is still hardening. Others propose that the groups may have congregated while mating.
The largest specimen of Isotelus rex, found in Manitoba, Canada measures 72 centimeters long. One specimen from Portugal measures 32 centimeters (13 inches) wide, and is preserved in a defensive, coiled position. If its entire length could be measured, it is believed that this specimen would measure 89.5 centimeters (almost 3 feet) long. Both the Portuguese trilobites and Isotelus lived during the Ordovician Period, what many consider to be the heyday of trilobites.
During the Ordovician, most of North America, where the largest Isotelus fossils were found, was in the tropics. The large size of Isotelus was previously explained by explained by high year long productivity. This was not the case with the Portuguese trilobites, at the time fragments of what would become the Iberian Peninsula where near the south pole. It is believed that these giant trilobites from Portugal exhibit polar gigantism, a found in many modern arthropods such as king crab.
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