Sunday, January 6, 2008

The Strangest Trilobites

Ceratarges, sculpted by Andrew Scott

When people think about trilobites, if they think about them at all, the mind will often conjure up an image of something half-way between a pill bug and a horseshoe crab. Generally speaking, many trilobites conform to this conceptualization, but, though trilobites usually adhere to this simple shape, there are some that are so sharply deviant as to seem utterly alien. This begins an examination of some of the most bizarre, and most intriguing trilobites ever to have been discovered. Their strange shapes are often suggestive of a discernible function of their once-living selves, but sometimes they inscrutably defy a simple explanation, and we are left with a lasting enigma.

Walliserops Trifurcatus

Walliserops trifurcatus, photo by Peter Cameron

Did Walliserops trifurcatus use its elongated, fork-like frontal projection to dig for soft bodied prey on the sandy sea floor? It would seem possible, yet we are unable to be sure without any direct evidence. Could the same structure have been a defensive adaptation, or have been brandished in ritual combat to determine sexual preference or to establish territory? Without the ability to directly observe their behavior, or to determine which trilobites were male or female, we can never know. Perhaps this trilobite's trident performed a combination of these functions, but maybe it was used for some unknown purpose.

Dicranurus1

Dicranurus monstrosus, photo by Peter Cameron

The twisted, horn-like projections on the cephalon of the aptly named Dicranurus monstrosus add to this trilobite's monstrous character. Coupled with the spiny extensions that fringe this trilobite's body, they readily suggest that this creature would have been a difficult meal to enjoy without injury. In the Devonian strata, fossils of suspected trilobite predators like ammonites and fish are also found abundantly, which would corroborate speculation about the structures' defensive purpose. But, were these spines dislodged during an attack, to be regenerated with successive molts? Were they strong enough to remain attached while repelling predators? Were they meant to cause internal injury as a warning against eating others of that species? Were they poisonous? Can we know the answers to these questions? The strangest trilobites silently defy our inquisition.

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